burial history of palaeozoic strata in belgium as revealed by conodont colour alteration data and thickness distributions thickness distributions of devono carboniferous formations and their relationship to conodont colour alteration indices cais from over 500 sample locations in belgium and northern france have been studied to reconstruct the thermal alteration and burial history of palaeozoic rocks the depositional centre during eifelian through visean times was located in the subsiding southern part of the dinant basin forming a thick sedimentary pile of probably more than 3 5 km in order to explain conodont cais chiefly resulting from upper carboniferous sedimentation two different depositional centres are considered giving rise to approximately 4 5 km of sediment in the central part of the dinant and namur basins as a consequence of the northward shifting variscan fold belt the upper carboniferous succession in the southern part of the dinant basin and in the rocroi area was reduced or absent conodont cais together with other thermal alteration data from the condroz massif indicate that this area was a structural high for most of the devonian the brabant massif was probably covered with approximately 1 5 2 0 km of upper carboniferous sediments in the south and less than 1 0 km in the central and northern parts in the central campine basin visean strata could have been buried by 3 5 4 5 km of upper carboniferous rocks

first permo carboniferous conodonts from north greenland upper palaeozoic conodonts are described for the first time from the north greenland wandel sea basin in eastern peary land the moscovian species idiognathodus incurvus and the kasimovian gzhelian i magnificus occur in the upper carboniferous foldedal formation while an assemblage from the lower part of the succeeding kim fjelde formation suggests deposition in the upper artinskian neostreptognathodus pequopensis n clarki zone these datings confirm the existence in the northern part of the wandel sea basin of the pronounced early permian hiatus previously recognized in holm land and amdrup land in the southern part of the basin the single conodont specimen found at prinsesse ingeborg halvo further corrobates the local absence of this regional hiatus in the central part of the wandel sea basin

development of strike slip faults from dikes sequoia national park california abstract faults several kilometers long near pear lake in sequoia national park california nucleated on preexisting dikes weakened by closely spaced echelon joints these joints essentially parallel much more widely spaced regional joints fault nucleation by dike fracturing can explain how a nearly planar fault can grow to lengths of several kilometers or more we suggest that opening mode fractures including dikes might serve more commonly as nuclei for faults than is generally appreciated the longest fault in the study area the pear lake fault has a trace length of 7 km and a maximum measured lateral separation of 86 98 m a sharp decrease in slip occurs near the center of the trace of the pear lake fault where another fault branches from it mechanical analyses demonstrate that a sharp decrease in slip is expected where a fault branches all the faults near pear lake show non elliptical slip distributions based on our mechanical analyses we infer that the observed slip distributions reflect a mechanical interaction among the faults the geometry and distribution of structures that precede faulting i e dikes and joints control to a large extent the structure of a fault network and hence the ultimate slip distribution on faults in the network

conodont color and textural alteration an index to regional metamorphism contact metamorphism and hydrothermal alteration experimental and field data are used to extend the utility of conodonts as semi quantitative thermal indices into the regimes of regional and contact metamorphism as well as hydrothermal alteration an arrhenius plot of data from induced conodont color alteration by pyrolysis in air at 1 atm was used to generate the geologic temperatures for conodont color alteration indices cai above 300 c that is for cai values of 5 through 8 such cai values occur in very low to medium grade regionally metamorphosed contact metamorphosed and hydrothermally altered rocks the uniformity or variability of cai values within a sample together with conodont texture can help to distinguish grades and environments of metamorphism particularly in metacarbonate sequences induced cai by pyrolysis in a water methane mixture at kbar results in retardation of cai and in a disparate mixture of both low and high cai values within each experimental sample in this system color alteration processes above a cai of 2 to 3 seem to change from predominantly carbonization to predominantly loss of organic matter presumably by oxidation and volatilization of oxides these experiments approximate the type of cai mixture characteristically found in conodonts recovered from hydrothermally altered rocks these data indicate that cai values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization

finite element modelling of atmosphere loading effects on strain tilt and displacement at multi sensor stations summary strain and tiltmeter observations are composed of signals of different origin tides are a wellknown phenomenon that can be extracted from the time series by tidal analysis depending on the location of the station residuals however contain contributions of different magnitudes from ocean loading changes in atmospheric or hydrological loading anthropogenic induced signals and tectonics reductions of the residual variations are indispensable for extraction of for example the pure tectonical signal one of the challenges in view of the reductions is to understand transfer mechanisms between loading and local conditions such as topography cavity and geological features which lead to additional or modified deformations in this study systematic numerical modelling using the finite element method with elastic rheology is carried out to estimate these effects barometric pressure changes are used as example for the load to determine the additional deformations strain and tiltmeters are considered as instrumentation having nominal resolutions of 0 2 nstrain and 1 nrad respectively the cavity and the topographic effect are systematically investigated with sophisticated models incorporating typical topographic features such as a plain a hill flank and a valley representative for stations worldwide four observatories in central europe are modelled the geodetic observatory wettzell germany the sopron observatory hungary the geodynamic observatory moxa and the black forest observatory bfo both germany the modelling shows that cavity and topographic effects occur in the same order of magnitude and that both effects interact leading to deformations partly intertwined in a complex way this notwithstanding the results explain observed deformation signals at the observatories the systematic modelling helps to better understand the basic processes from which criteria for the selection of future observation sites are inferred

the broadband seismic station cadi tunel del cadi eastern pyrenees part ii long period variations of background noise the aim of this work is to complement a previous article by vila 1998 presenting long term observations of the behavior of seismic noise we start by computing the fourier transforms ffts of time series 30 min length one series per day of the last 6 years of operation in an attempt to confirm whether the observations follow the pattern observed in the previous analysis the analysis of the microseismic peak using 6 years of data confirms a long time seasonal variation of the amplitude showing in addition the same variation in the frequency at which the maximum occurs this points out the necessity of clarifying some of the observations in vila 1998 and some modification in the conclusions is also necessary a detailed analysis of the behavior of several spectral components of the seismic noise reveals that the seasonal component is presented in the frequency range 0 05 2 0 hz the amplitude of the seasonal component has a clear frequency dependence being higher for frequencies close to the microseismic peak the main differences between the spectral components are in accordance with its own amplitude level no significant differences between the behavior of noise of the three components have been reported although for the geographical location of the station the seasonal component is present in the atmospheric pressure all attempts of correlation with seasonal components for diverse frequencies of the noise spectra have failed this indicates that the pressure seasonal component cannot be related directly to the same component of the very long term noise spectral evolution manuscript received 18 january 2002

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

on diagenesis dolomitisation and mineralisation in the irish zn pb orefield marine calcite cementation and lithification of carboniferous carbonate sediments hosting zn pb mineralisation in the irish orefield occurred at or near the seafloor a relatively early fine grained grey replacive dolomite preferentially developed in micrite is widely developed in the waulsortian limestone formation the main host to mineralisation and is pervasive in the southeastern midlands in proximity to the leinster massif this dolomite formed after the first four main stages of calcite cementation but probably also developed within tens of metres of the seafloor as evidenced by incorporation of clasts of dolomite in intraformational sedimentary breccias later coarse grained white dolomite preferentially replaced coarser components of the waulsortian limestone and infilled residual vuggy porosity whilst some of this coarse dolomite may be related to the fine replacive dolomite event a common spatial association with fault zones coupled with primary fluid inclusion data suggest that a significant proportion of this phase precipitated during the onset of fault controlled subsidence and widespread hydrothermal circulation within the irish midlands area fluids up to 250 c and 10 15 wt nacl equivalent sourced from a lower palaeozoic basement equilibrated fluid reservoir infiltrated the carbonate sequence via faults and fractures the more localised development of dolomite cemented breccias white matrix breccias that are frequently associated spatially with mineralisation was a consequence of the increased focusing of these hydrothermal fluids ore formation was broadly synchronous with development of the white dolomite breccias but only happened where mixing occurred between the hydrothermal ore fluids and localised near surface reservoirs of low temperature h2s rich brine in the waulsortian this process led to the precipitation of a distinctive black dolomite that forms a broad halo to massive sulphides although ore stage sulphides postdate significant diagenesis of the host rocks and often display epigenetic textures the fact that much of the cementation occurred soon after carbonate deposition means that mineralisation does not have to have formed after significant burial in fact the occurrence of clasts of hydrothermal dolomite and sulphides in intraformational debris flow breccias is only consistent with mineralising processes occurring in the near seafloor environment relatively soon after host rock deposition the regional development of a distinctive pink dolomite associated with faults and fractures was a post ore event and is considered to mark a regional brine migration linked to the onset of the variscan orogeny the development of this new tectonic and flow regime may have been responsible for the cessation of economic mineralisation in ireland

on deck seismology lessons from insight for future planetary seismology before deploying to the surface of mars the short period sp seismometer of the insight mission operated on deck for a total of 48 hr this data set can be used to understand how deck mounted seismometers can be used in future landed missions to mars europa and other planetary bodies while operating on deck the sp seismometer showed signals comparable to the viking 2 seismometer near 3 hz where the sensitivity of the viking instrument peaked wind sensitivity showed similar patterns to the viking instrument although amplitudes on insight were 80 larger for a given wind velocity however during the low wind evening hours the instrument noise levels at frequencies between 0 1 and 1 hz were comparable to quiet stations on earth although deployment to the surface below the wind and thermal shield lowered installation noise by roughly 40 db in acceleration power with the observed noise levels and estimated seismicity rates for mars detection probability for quakes for a deck mounted instrument is low enough that up to years of on deck recordings may be necessary to observe an event because the noise is dominated by wind acting on the lander though deck mounted seismometers may be more practical for deployment on airless bodies and it is important to evaluate the seismicity of the target body and the specific design of the lander detection probabilities for operation on europa reach over 99 for some proposed seismicity models for a similar duration of operation if noise levels are comparable to low wind time periods on mars

existence of the threshold pressure for seismic excitation by atmospheric disturbances excitation of seismic waves by atmospheric pressure changes is examined from data for two tropical cyclones tropical storm lee 2011 and hurricane isaac 2012 they moved through the earthscope transportable array ta and generated variations in pressure and ground motions that spanned 4 5 orders of magnitude in power spectral density psd for vertical seismic ground velocity psd sv for frequencies between 0 01 and 0 02 hz there is a threshold pressure at about pressure psd sp of 10 pa2s below which vertical motion is not affected by local atmospheric pressure above this threshold pressure vertical ground motion increases with surface pressure as sv sp1 5 in order to understand the land atmosphere interaction pressure above this threshold is the only useful range horizontal component psds are about two orders of magnitude larger than vertical component psds and change with pressure for its entire range this overall trend is most likely caused by ground tilt

infrared spectroscopy of triassic conodonts a new tool for assessing conodont diagenesis the fourier transform infrared spectra of individual conodonts with various cai values indicate definite changes in conodont francolite during diagenesis steady decarbonation can be observed in the increasing intensity of the band with the wavenumber 2340 an 1 which is assigned to trapped molecular co2 carbon dioxide originates from decomposing co2 3 ions occupying the b site in francolite furthermore the intensity of the water deformation band at 1644 cm 1 decreases with higher cai values these changes of intensity can be quantified by calculating the maximum extinction emax for the corresponding absorption maxima and correlated with the cai unaltered conodonts have a relative variable water content and very little co2 up to a cai value of 4 conodont francolite continuously expells water and carbon dioxide is trapped conodonts with cai 5 have similar water contents to cai 4 conodonts but decarbonation continues to take place during this stage of diagenesis

characterizing swells in the southern pacific from seismic and infrasonic noise analyses a temporary network of 10 broad band seismic stations has been installed in french polynesia for the polynesian lithosphere and upper mantle experiment plume all the seismic stations were installed either on volcanic islands or on atolls of the various archipelagos of french polynesia in a manner which complements the geographic coverage provided by the regional permanent stations the primary aim of plume is to image the upper mantle structures related to plate motion and hotspot activity however because of its proximity to all sites the ocean is responsible for a high level of noise in the seismic data and we show that these data can also be used to analyse ocean wave activity the power spectral density psd analyses of the seismic data recorded in french polynesia show clear peaks in the 0 05 0 10 hz band periods between 10 and 20 s which corresponds to swell frequencies clear peaks in this frequency band are also observed in infrasonic data recorded on tahiti ground motion analysis shows that the swell related seismic noise srsn is linearly polarized in the horizontal plane and its amplitude decreases rapidly with the distance from the shore the microseismic and the infrasonic noise amplitudes show very similar variations from station to station and both are strongly correlated with the swell amplitudes predicted by the national oceanic and atmospheric administration noaa wind forced wavewatch models the swell direction can be estimated from srsn polarization analysis but this has to be done with care since for some cases the ground motions are strongly controlled by the islands anisometric shapes and by swell refraction processes we find cases however such as tahiti or roughly circular tuamotu atolls where the azimuth of the swell is in good agreement with the seismic estimates we therefore demonstrate that the srsn and the infrasonic signal observed in french polynesia can be used in such cases as a proxy for swell amplitude and azimuth from the continuous analysis of the data recorded in 2003 at the permanent seismic station pptl in tahiti transfer functions have been obtained this could provide a way to quantify the swell activity during the last two decades and therefore assist in the investigation of climate changes

dust devil track survey at elysium planitia mars implications for the insight landing sites abstract the insight interior exploration using seismic investigations geodesy and heat transport robotic lander is scheduled to land in elysium planitia on mars in september 2016 insight will perform the first comprehensive surface based geophysical investigation including seismic measurements knowledge about encounter rates of dust devils with the insight lander are important for two main reasons 1 dust devils will affect the scientific measurements i e wind induced seismic noise and 2 the power supply of the insight lander and instruments is provided by solar arrays and previous landers and rovers on mars were affected by a steady decline in electrical power output due to atmospheric dust deposition on the solar panels long term science operations were only made possible by dust clearing events of the solar arrays caused by wind gusts and dust devils in this study we analyzed dust devil tracks ddts at the final insight landing site region in elysium planitia formation of ddts is caused by the removal of a layer of dust by passing dust devils hence in principle the same process as clearing of dust from solar panels we mapped the number size width and length and orientation of ddts in repeat observations using high resolution imaging science experiment hirise images covering the exact same surface area acquired within a relatively short time span l s 200 consistent with the seasonal reversal in direction of the hadley circulation ddt formation rates vary between 0 002 and 0 08 ddt km 2 sol 1 ddt area formation rates using the measured ddt widths lengths and formation rates are in the range of 0 0003 0 00006 km 2 km 2 sol 1 implying that a given spot on the surface may be cleared of dust only once between 3000 and 16 000 sols i e every 5 24 mars years measured ddt formation rates were used to find a scaling factor to the seasonal dda index and then integrated over the year to estimate a mean annual ddt formation rate of 0 046 ddt km 2 sol 1 this translates into a solar panel clearing recurrence interval estimate of 11 mars years using the mean annual ddt formation rate and the mean ddt width and length from all measured ddts due to several uncertainties this solar panel clearing recurrence interval for the insight landing should be seen as an upper limit estimate

conodont colour alteration indices palaeotemperatures and metamorphism in the northern calcareous alps a general view the middle and eastern parts of the northern calcareous alps nca can be subdivided into two distinct units with a lateral boundary marked by abrupt changes in the conodont colour alteration index cai values the first of these is a northern unit tirolikum with a relatively homogeneous distribution of no or low grade conodont alteration cai 1 0 2 0 the thermal overprint is thought to be relatively young and related to a heat flow from the tauern crystallization the second unit consists of the juvavic nappe system juvavikum which is distributed along the southern rim of the nca but also covers some of the northern parts of the tirolikum with respect to its cai distribution the juvavikum is more heterogeneous on a regional and local scale with some local cai inversions the juvavikum additionally shows distinctly different sets of cai values one with weak cai 1 0 1 5 and another with strong alteration cai 5 5 7 0 at present the highest known thermal overprint measured in the nca the metamorphism is relatively old as it predates the late jurassic early cretaceous gravity tectonic emplacement of the juvavikum onto the tirolikum the high cai values of parts of the juvavic nappe system are though to be related to tectonic burial in an accretionary wedge formed parallel to the closure of the vardar ocean the low cai values of the tirolikum apparently exclude a direct juxtaposition of the two units at the time of metamorphism

formation of compound strike slip fault zones mount abbot quadrangle california abstract numerous strike slip fault zones in granitic rocks of the mount abbot quadrangle california developed from steeply dipping subparallel joints these joints generally were less than 50 m long and were spaced several centimeters to several meters apart some joints subsequently slipped and became small faults simple fault zones formed as oblique dilatant fractures splay fractures linked non coplanar faults side to side and end to end these simple fault zones are as much as 1 km long and accommodated displacements as great as 10 m compound fault zones formed as splay fractures linked small faults and simple fault zones they are as much as several kilometers long and accommodated displacements as great as 100 m these zones are distinctly different from riedel shear zones and the mechanics of their formation are unlikely to be described well by mohr coulomb mechanisms simple and compound fault zones are composed of non coplanar segments that join at steps or bends splay fracture length determines step widths the longest splay fractures occur along the longest fault zones allowing step widths to increase as the length and displacement across the zones increase these findings are consistent with the structure of some active seismogenic faults and they provide a mechanically consistent field based conceptual model for fault zones that grow in basement rocks from a preexisting set of joints

the relationship between length and width of plutons within the crustal scale cobequid shear zone northern appalachians canada the lengths and widths have been measured for 69 component bodies of composite plutons along the cobequid shear zone plutons on major fault strands those with mylonite zones 0 1 km wide exhibit evidence of multiple intrusion of magma batches small plutons along short faults in stepover zones appear related to rapid emplacement of magma in bodies 1 5 4 km long by 0 1 2 km wide such small plutons show low enrichment in incompatible elements in older component bodies but increasing amounts in younger bodies as a result of progressive magma expulsion from crystal mush during crystallization and shear enhanced compaction in fault zones wider plutons generally occur along longer fault strands accommodating more strain and penetrating deeper into the crust and show enrichment in incompatible elements the width of the mylonitic fault zone is about 15 of the width of these plutons the length to width ratio of component bodies and composite plutons varies between 2 and 11 the best fit line describing these data has a slope of 1 056 which implies scaling behavior between plutonism and tectonic processes scalar properties of plutonic bodies are similar to those of faults but scalar relationships observed in component bodies do not apply to composite plutons

overlooked earthquakes on and around the antarctica plate identification and location of 1999 shallow depth events abstract as a contribution to the study of high latitude seismicity on the antarctica plate we have developed a procedure to identify and locate previously unnoticed earthquakes by using broadband records of 29 stations operating in the southern hemisphere a first approach of the method consists of visually examining continuous records from geoscope and gsn stations for rayleigh waves associated with earthquakes missing in the neic monthly catalogue two hundred ten earthquakes were identified that had no corresponding locations in the 1999 neic catalogue among them 88 events with magnitude ranging from 3 7 to 5 2 and identified on at least four stations have been located by using an epicenter location algorithm based on regional rayleigh wave propagation models the precision of the location depending both on the selected propagation model and the phase picking accuracy is around 100 km most of the reported earthquakes occurred on the plate boundaries principally along the south indian and pacific ridges a few epicenters have been located inside the antarctica plate far from the plate limits among them only two earthquakes occurring on the continent itself are reported about half of the events located in our study are reported by the pidc prototype international data center three earthquakes with magnitudes ranging from 4 7 to 5 2 reported neither by neic nor by pidc are sufficiently energetic to be recorded in most broad band stations operating around the world considerations concerning the local crustal structure and the physical processes at the source are involved in interpreting these observations

brittle ductile brittle deformation during cooling of tonalite adamello southern italian alps abstract late to post magmatic deformation in slightly diachronous contiguous intrusions of the north western adamello batholith southern alps italy is recorded as from oldest to youngest i joints ii solid state ductile shear zones iii faults associated with epidote k feldspar veins and iv zeolite veins and faults structures ii to iv are localized on the pervasive precursory network of joints i which developed during the earliest stages of pluton cooling high temperature 500 c ductile overprinting of joints produced lineations defined by aligned biotite and hornblende on the joint surfaces and highly localized mylonites the main phase of faulting producing cataclasites and pseudotachylytes occurred at 250 c and was associated with extensive fluid infiltration cataclasites and pseudotachylytes are clustered along different e w striking dextral strike slip fault zones correlated with the activity of the tonale fault a major tectonic structure that bounds the adamello batholith to the north ductile deformation and cataclastic veining episodes occurred at p 0 25 0 3 gpa during rapid cooling of the batholith to the ambient temperatures 250 c that preceded the exhumation of the batholith timing of the sequence of deformation can be constrained by 39 ar 40 ar ages of 30 ma on pseudotachylytes and various existing mineral ages in the whole composite adamello batholith multiple magma pulses were intruded over the time span 42 30 ma and each intrusive body shows the same ductile to brittle structural sequence localized on the early joint sets this deformation sequence of the adamello might be typical of intrusions undergoing cooling at depths close to the brittle ductile transition

nucleation of ductile shear zones on dilatant fractures small shear zones in granitic rocks of the sierra nevada california and near roses rosas northeast spain display features which indicate that dilatant fracturing preceded the localization of ductile shear deformation many zones have sharp nearly planar boundaries between their highly deformed interiors and the undeformed wall rock the roses shear zones narrow continuously to hairline fractures at their ends mineralized microcracks oriented parallel to the shear zones cluster near the zone boundaries and are interpreted as relicts of the earlier fracturing episode dynamic recrystallization of minerals filling these microcracks demonstrates that fracturing predated the ductile deformation gradients in ductile strain suggest that deformation spread laterally into the wall rocks after nucleation of the shear zones we suggest that cracks enhance the wall rock ductility by increasing local fluid fluxes thereby promoting chemical alteration and or hydrolytic weakening

tabular fracture clusters dynamic fracturing produced by volatile expulsion sierra nevada batholith california abstract an undocumented type of fracture system tabular fracture clusters tfcs occurs in the cathedral peak granodiorite sierra nevada batholith ca tfcs are linear zones of sub parallel densely spaced fractures approximately 4 40 cm wide and 3 100 m long tfcs occur in highest density adjacent to the johnson granite porphyry which intruded the cathedral peak granodiorite individual fractures in tfcs exhibit only opening mode displacement microstructural analysis indicates that tfc fractures contain micro breccia of angular clasts of host rock fine grained zeolite and quartz are observed along many of the fractures within tfcs all of which are absent in the host rock the characteristics of tfcs suggest that they differ from previously documented fracture systems in the sierra nevada batholith the dense spacing nature of the fractures and association of tfcs with miarolitic cavities provide compelling evidence that tfcs formed in response to volatile overpressure from the adjacent johnson granite porphyry we attribute the formation of tfcs to dynamic fracturing based on the clustered nature of the extension fractures and the geometric similarities of tfcs to other dynamic fracturing arrays

greenland fracture zone east greenland ridge s revisited indications of a c22 change in plate motion 1 changes in the lithospheric stress field causing axial rift migration and reorientation of the transform are generally proposed as an explanation for anomalously old crust and or major aseismic valleys in oceanic ridge transform ridge settings similarly transform migration of the greenland fracture zone and separation of the 200 km long fracture zone parallel continental east greenland ridge from the eurasia plate is thought to be related to a major change in relative plate motions between greenland and eurasia during the earliest oligocene chron 13 time this study presents a reinterpretation of the greenland fracture zone east greenland ridge based on new and existing geophysical data evidence is shown for two overstepping ridge segments segments a and b of which segment a corresponds to the already known east greenland ridge while segment b was not detected previously interpretation of sonobuoy data and revised modeling of existing obs data across segment b indicate a continental composition of the segment this interpretation is supported by magnetic anomaly data the segments a and b are bounded by portions of the greenland fracture zone with a distinct 10 difference in strike this is suggested to relate to an early episode of transform migration and reorientation of the lithospheric stress field around chron 22 time i e shortly after the eocene breakup in the northern ne atlantic these findings contradict with previous interpretations of the fracture zone which infer simple pre c13 strike slip kinematics

the temporal relationship between joints and faults abstract examples are presented of three temporal relationships between joints and faults joints that pre date faults joints that are precursors to or synchronous with faults and joints that post date faults emphasis is placed on strike slip faults in carbonate beds but other examples are used general rules are given for identifying the three temporal relationships between joints and faults joints that formed before faults can be dilated sheared or affected by pressure solution during faulting depending on their orientation in relation to the applied stress system faulted joints can preserve some original geometry of a joint pattern with pinnate joints or veins commonly developing where faulted joints interact joints formed synchronously with faults reflect the same stress system that caused the faulting and tend to increase in frequency toward faults in contrast joints that pre or post date faults tend not to increase in frequency towards the fault joints that post date a fault may cut across or abut the fault and fault related veins without being displaced by the fault they may also lack dilation near the fault even if the fault has associated veins joints formed either syn or post faulting may curve into the fault indicating stress perturbation around the fault different joint patterns may exist across the fault because of mechanical variations geometric features may therefore be used in the field to identify the temporal relationships between faults and joints especially where early joints affect or control fault development or where the distribution of late joints are influenced by faults

thermal maturation of the lower palaeozoic strata of northern greenland from conodont colour alteration index cai data implications for burial history and hydrocarbon exploration conodont colour alteration data for the lower palaeozoic strata of the north greenland carbonate platform indicate a pattern of increased thermal maturity northwards within the franklinian basin there is little variation in values through the canadian llandovery lower ordovician lower silurian interval at any given locality a simplified thermal model for the platform suggests that the predominant control of conodont colour alteration and thermal maturation was maximum depth of burial which occurred during the mid to late silurian a preliminary integrated scheme for conodont and organic thermal maturity indicators can be compiled from the data now available from north greenland

fault welding by pseudotachylyte formation during earthquakes melt produced by frictional heating can accumulate on slip surfaces and dramatically weaken faults by melt lubrication once seismic slip slows and arrests the melt cools and solidifies to form pseudotachylytes the presence of which is commonly used by geologists to infer earthquake slip on exhumed ancient faults field evidence suggests that solidified melts may weld seismic faults resulting in subsequent seismic ruptures propagating on neighboring pseudotachylyte free faults or joints and thus leading to long term fault slip delocalization for successive ruptures we performed triaxial deformation experiments on natural pseudotachylyte bearing rocks and show that cooled frictional melt effectively welds fault surfaces together and gives faults cohesive strength comparable to that of an intact rock consistent with the field based speculations further shear is not favored on the same slip surface but subsequent failure is accommodated on a new subparallel fault forming on an off fault preexisting heterogeneity a simple model of the temperature distribution in and around a pseudotachylyte following slip cessation indicates that frictional melts cool to below their solidus in tens of seconds implying strength recovery over a similar time scale

slip accumulation and lateral propagation of active normal faults in afar we investigate fault growth in afar where normal fault systems are known to be currently growing fast and most are propagating to the northwest using digital elevation models we have examined the cumulative slip distribution along 255 faults with lengths ranging from 0 3 to 60 km faults exhibiting the elliptical or bell shaped slip profiles predicted by simple linear elastic fracture mechanics or elastic plastic theories are rare most slip profiles are roughly linear for more than half of their length with overall slopes always 0 035 for the dominant population of nw striking faults and fault systems longer than 2 km the slip profiles are asymmetric with slip being maximum near the eastern ends of the profiles where it drops abruptly to zero whereas slip decreases roughly linearly and tapers in the direction of overall aden rift propagation at a more detailed level most faults appear to be composed of distinct shorter subfaults or segments whose slip profiles while different from one to the next combine to produce the roughly linear overall slip decrease along the entire fault on a larger scale faults cluster into kinematically coupled systems along which the slip on any scale individual fault or fault system complements that of its neighbors so that the total slip of the whole system is roughly linearly related to its length with an average slope again 0 035 we discuss the origin of these quasilinear asymmetric profiles in terms of initiation points where slip starts and barriers where fault propagation is arrested in the absence of a barrier slip apparently extends with a roughly linear profile tapered in the direction of fault propagation

microtremor observations of deep sediment resonance in metropolitan memphis tennessee we measured site resonance periods throughout metropolitan memphis tennessee the site resonance was derived from recordings of ambient microtremor and is a direct measurement of seismic ground shaking in the memphis metropolitan area the period t0 in s is predicted by the empirical relation t0 0 39899 7 8922 10 3h 3 0634 10 6h2 350 h 1100 m where h is the thickness in m of the unconsolidated sediments that overly hard paleozoic rocks assuming that a quarter wavelength relationship governs the relationship between resonant period sediment thickness and average shear wave speed we estimate the average shear wave speed of unconsolidated sediments as a function of sediment thicknesses vs 521 15 0 37459h 350 h 1100 m the scatter in the observations and discordance with earlier work suggests that caution is warranted in applying these values of wave speed indiscriminately to sites in the absence of further detailed work

eurekan transpressive deformation in the wandel hav mobile belt northeast greenland 1 besides the w e trending kap cannon thrust zone and harder fjord fault zone the 300 km long and nw se striking wandel hav mobile belt represents the third major fault zone in north greenland structural analyses in several areas of this belt suggest that compressive deformation is characterized by transpressive dextral strike slip kinematics this is demonstrated by a combination of folding around w e axes approximately north and south directed reverse faulting and dextral strike slip displacements along nw se trending fault lines the initial formation of the long linear faults is interpreted to be related to deformational events in late paleozoic triassic jurassic and late cretaceous times due to the lack of structural evidence we assume that deformations led to the generation of extension faults which probably were reactivated during dextral strike slip tectonism it is suggested that dextral transpressive deformation was coeval with n s compression at the harder fjord fault zone and cap cannon thrust zone and took place during eocene eurekan times dextral strike slip tectonism in the wandel hav mobile belt was the result of n s compression due to a general northward movement of the greenland plate as a zone of crustal weakness the belt can be interpreted as the onshore equivalent of the main transcurrent fault zone de geer fault which caused the intracontinental dextral slip of svalbard barents shelf relative to north greenland during early tertiary eurekan times and prior to their separation in this configuration it represents one part of the belt of eurekan deformation which extends from the canadian arctic islands over north greenland to the barents shelf where compressive deformation is recorded in the west spitsbergen fold and thrust belt

pressure effects on the seis insight instrument improvement of seismic records and characterization of long period atmospheric waves from ground displacements mars atmospheric pressure variations induce ground displacements through elastic deformations the various sensors of the insight mission were designed in order to be able to understand and correct for these ground deformations induced by atmospheric effects particular efforts were made on one hand to avoid direct pressure and wind effects on the seismometer and on the other hand to have a high performance pressure sensor operating in the same frequency range as the seismometer as a consequence of these technical achievements and the low background seismic noise of mars the insight mission is opening a new science domain in which the ground displacements can be used to perform atmospheric science this study presents an analysis of pressure and seismic signals and the relations between them after a short description of the pressure and seismic sensors we present an analysis of these signals as a function of local time at the insight location then the coherent signals recorded by both pressure and seismic sensors are described and interpreted in terms of atmospheric signals and ground deformation processes two different methods to remove the pressure effects recorded by seis sensors are presented and their efficiency is estimated and compared these decorrelation methods allow the pressure generated noise to be reduced by a factor of two during the active day time period finally an analysis of seis signals induced by gravity waves demonstrates the interest of ground displacement measurements to characterize their arrival azimuth

uranium lead isotopic ages from the sierra nevada batholith california this study provides new information on the timing and distribution of mesozoic magmatic events in the sierra nevada batholithic complex chiefly between 36 and 37 n latitude u pb ages have been determined for 133 zircon and 7 sphene separates from 82 samples of granitoid rocks granitoid rocks in this area range in age from 217 to 80 m y triassic intrusions are restricted to the east side of the batholith jurassic plutons occur south of the triassic plutons east of the sierra nevada as isolated masses within the cretaceous batholith and in the western foothills of the range cretaceous plutons form a continuous belt along the axis of the batholith and occur as isolated masses east of the sierra nevada no granitic intrusions were emplaced for 37 m y east of the sierra nevada following the end of jurassic plutonism however following emplacement of the eastern jurassic granitoids regional extension produced a fracture system at least 350 km long into which the dominantly mafic calc alkalic independence dike swarm was intruded 148 m y ago the dike fractures probably represents a period of regional crustal extension caused by a redistribution of the regional stress pattern accompanying the nevadan orogeny intrusion of cretaceous granitic plutons began in large volume about 120 m y ago in the western sierra nevada and migrated steadily eastward for 40 m y at a rate of 2 7 mm y this slow and constant migration indicates remarkably uniform conditions of subduction with perhaps downward migration of parent magma generation or a slight flattening of the subduction zone such steady conditions could be necessary for the production of large batholithic complexes such as the sierra nevada the abrupt termination of plutonism 80 m y ago may have resulted from an increased rate of convergence of the american and eastern pacific plates and dramatic flattening of the subduction zone u pb ages of the giant forest alaskite sequence in sequoia national park are all in the range 99 3 m y indicating a relatively short period of emplacement and cooling for this nested group of plutons u pb ages of a mafic inclusion and its host granodiorite indicate that both were derived from a common source or that the mafic inclusion was totally equilibrated with the granodioritic magma comparison of isotopic ages determined by different methods such as zircon u pb sphene u pb hornblende k ar and biotite k ar suggests that zircon u pb ages generally approximate the emplacement age of a pluton however some plutons probably contain inherited or entrained old zircons and the zircons of some samples are disturbed by younger thermal and metamorphic events the ages reported here are consistent with u pb age determinations previously made on granitic rocks to the north stern et al 1981 the age distribution of granitic belts determined here is in general agreement with those established by k ar dating evernden and kistler 1970 but does not differentiate the five epochs of plutonism determined in their study

constraints on the shallow elastic and anelastic structure of mars from insight seismic data mars s seismic activity and noise have been monitored since january 2019 by the seismometer of the insight interior exploration using seismic investigations geodesy and heat transport lander at night mars is extremely quiet seismic noise is about 500 times lower than earth s microseismic noise at periods between 4 s and 30 s the recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground transferred wind generated lander noise here we constrain properties of the crust beneath insight using signals from atmospheric vortices and from the hammering of insight s heat flow and physical properties hp3 instrument as well as the three largest marsquakes detected as of september 2019 from receiver function analysis we infer that the uppermost 8 11 km of the crust is highly altered and or fractured we measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the moon which suggests that the crust contains small amounts of volatiles the crust beneath the insight lander on mars is altered or fractured to 8 11 km depth and may bear volatiles according to an analysis of seismic noise and wave scattering recorded by insight s seismometer

late palaeozoic evolution of the north atlantic margin of pangea abstract eleven palaeogeographic maps spanning the earliest carboniferous tournaisian to late permian kazanian have been constructed for the northern north atlantic based on available onshore and offshore data each palaeogeographic map corresponds to an epoch i e 4 17 ma there are no reconstructions of the serpukhovian and tatarian and the kungurian ufimian are treated as one the palaeogeographic reconstructions outline a change in the overall depositional environment of the barents sea north greenland area from huge humid flood plains in the early carboniferous over shallow warm seas in the mid carboniferous to mid permian to cooler and possibly deeper marine environments in the late permian in east greenland non marine conditions occurred during the entire carboniferous and following a prolonged early permian hiatus warm water carbonates were deposited during the late permian the changes reflect large scale shifts in palaeoclimatic and subsidence patterns related to the northward drift of the area and ongoing rifting in the region

on reduction of long period horizontal seismic noise using local barometric pressure summary tilt from atmospheric loading has long been known to be the major source of long period horizontal seismic noise we try to quantify these effects for seismic data from the black forest observatory bfo which is known to be a very quiet station experimental transfer functions between local barometric pressure and horizontal seismic noise are estimated for two long time series by standard methods two simple analytical physical models are developed the local deformation model ldm and the acoustic gravity wave model twm subsequently these models with only two free parameters are fit using least squares to the observed seismic noise for time series of widely differing lengths the results are variable sometimes rather dramatic variance reductions are obtained and sometimes the reduction is hardly significant the method produces the best results when barometrically induced noise is high the resulting admittances for the ldm are compared to finite element calculations since the methods are simple and can result in conspicuous reductions in noise we provide one more reason for installing barometers at even the best broad band seismic stations

growth linkage and termination processes of a 10 km long strike slip fault in jointed granite the gemini fault zone sierra nevada california abstract field based structural analysis of an exhumed 10 km long strike slip fault zone elucidates processes of growth linkage and termination along moderately sized strike slip fault zones in granitic rocks the gemini fault zone is a 9 3 km long left lateral fault system that was active at depths of 8 11 km within the transpressive late cretaceous sierran magmatic arc the fault zone cuts four granitic plutons and is composed of three steeply dipping northeast and southwest striking noncoplanar segments that nucleated and grew along preexisting cooling joints the fault core is bounded by subparallel fault planes that separate highly fractured epidote chlorite and quartz breccias from undeformed protolith the slip profile along the gemini fault zone shows that the fault zone consists of three 2 3 km long segments separated by two zones of local slip minima slip is highest 131 m on the western third of the fault zone and tapers to zero at the eastern termination slip vectors plunge shallowly west southwest and show significant variability along strike and across segment boundaries four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at or below greenschist facies conditions taken together we interpret the fault zone to be a segmented linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations complex fault segment interactions and asymmetric slip distance profiles

wind induced ground motion wind noise is a problem in seismic surveys and can mask the seismic signals at low frequency this research investigates ground motions caused by wind pressure and shear stress perturbations on the ground surface a prediction of the ground displacement spectra using the measured ground properties and predicted pressure and shear stress at the ground surface is developed field measurements are conducted at a site having a flat terrain and low ambient seismic noise triaxial geophones are deployed at different depths to study the wind induced ground vibrations as a function of depth and wind velocity comparison of the predicted to the measured wind induced ground displacement spectra shows good agreement for the vertical component but significant underprediction for the horizontal components to validate the theoretical model a test experiment is designed to exert controlled normal pressure and shear stress on the ground using a vertical and a horizontal mass spring apparatus this experiment verifies the linear elastic rheology and the quasi static displacements assumptions of the model the results indicate that the existing surface shear stress models significantly underestimate the wind shear stress at the ground surface and the amplitude of the fluctuation shear stress must be of the same order of magnitude as the normal pressure measurement results show that mounting the geophones flush with the ground provides a significant reduction in wind noise on all three components of the geophone further reduction in wind noise with depth of burial is small for depths up to 40 cm

strike slip fault terminations at seismogenic depths the structure and kinematics of the glacier lakes fault sierra nevada united states 1 structural complexity is common at the terminations of earthquake surface ruptures similar deformation may therefore be expected at the end zones of earthquake ruptures at depth the 8 2 km long glacier lakes fault glf in the sierra nevada is a left lateral strike slip fault with a maximum observed displacement of 125 m within the fault pseudotachylytes crosscut cataclasites showing that displacement on the glf was accommodated at least partly by seismic slip the western termination of the glf is defined by a gradual decrease in the displacement on the main fault accompanied by a 1 4 km wide zone of secondary faulting in the dilational quadrant of the glf the secondary faults splay counterclockwise from the main fault trace forming average angles of 39 with the main fault slip vectors defined by slickenlines plunge more steeply west for these splay faults than for the glf static stress transfer modeling shows that the orientations of the splays and the plunge of displacement on those splays are consistent with displacement on the main fault the glf termination structure shows that structural complexity is present at the terminations of faults at seismogenic depths and therefore ruptures that propagate beyond fault terminations or through step overs between two faults will likely interact with complex secondary fault structures models of dynamic rupture propagation must account for the effect of preexisting structures on the elastic properties of the host rock additionally aftershock distributions and focal mechanisms may be controlled by the geometry and kinematics of structures present at fault terminations

modeling the excitation of seismic waves by the joplin tornado tornadoes generate seismic signals when they contact the ground here we examine the signals excited by the joplin tornado which passed within 2 km of a station in the earthscope transportable array we model the tornado generated vertical seismic signal at low frequencies 0 01 0 03 hz and solve for the strength of the seismic source the resulting source amplitude is largest when the tornado was reported to be strongest ef 4 5 and the amplitude is smallest when the tornado was weak ef 0 2 a further understanding of the relationship between source amplitude and tornado intensity could open up new ways to study tornadoes from the ground

reflectance measurements of zooclasts and solid bitumen in lower paleozoic shales southern scandinavia correlation to vitrinite reflectance abstract reflectance measurements have been carried out on zooclasts graptolites chitinozoans and vase shaped microfossils and other organic particles vitrinite like particles porous granular vitrinite like particles and solid bitumen in middle cambrian to upper silurian shales from central and southern sweden and the danish island of bornholm baltic sea the most abundant organic components in all the shales are fragments of graptolites and vitrinite like particles the reflectance distribution of these two types of components is largely identical and it is suggested that the vitrinite like particles are fragments of graptolites without any recognizable morphology reflectance measurements of graptolites and vitrinite like particles yield well defined reflectance populations in samples with average r graptolite and average r vitrinite like of 0 75 r o the reflectance distributions are bimodal because of increasing bireflectance and the average reflectance value of the well defined lower reflecting population is arbitrarily used as maturity indicator our results suggest that with increasing thermal maturity the reflectance of graptolites increases faster than the predicted vitrinite reflectance the relationship between graptolite reflectance and equivalent vitrinite reflectance can be expressed by the equation vr eqv 0 73 r graptolite vitrinite like low 0 16 the gas generation window which normally is considered to begin at a vitrinite reflectance of 1 3 r o in post lower paleozoic rocks containing vitrinite starts accordingly at 1 56 r o graptolite reflectance porous granular vitrinite like particles occur in minor amounts and they may represent graptolite fragments with a non smooth surface they generally yield slightly higher reflectance than non granular vitrinite like particles and graptolite fragments the middle cambrian to furongian upper cambrian shales may contain sparse fragments of vase shaped microfossils vsm that seem to follow the maturation trend of chitinozoans in the present sample set the reflectance of chitinozoans and vsm is comparable to that of graptolites at the same level of maturity reflectance measurements of solid bitumen are a poor maturity indicator probably because bitumen can have various origins and morphologies and it may not be indigenous to the host rock

evidence of atmospheric gravity waves during the 2008 eruption of okmok volcano from seismic and remote sensing observations 1 okmok volcano erupted on july 12 2008 following an 11 year hiatus detailed inspection of the syn eruptive seismograms revealed the presence of an ultra long period mode at a frequency of 1 7 mhz which is not a characteristic of the background seismic noise at okmok data collected by the national oceanic and atmospheric administration geostationary operational environmental satellite goes and national aeronautical and space administration moderate resolution imaging spectroradiometer modis sensors displayed the propagation of a vigorous ash and steam plume up to about 17 km above sea level we suggest that the observed ultra long period signals represent the response of the seismometer to changes in gravity associated with buoyancy oscillations set off in the lower atmosphere above okmok by the emplacement of the eruption column calculations based on simple modeling of these effects allowed estimation of peak atmospheric pressure perturbations associated with the eruption of less than 1 mbar

intra arc strike slip fault exposed at batholithic levels in the southern sierra nevada california the kern canyon fault is a major north trending fault that is continuous for a distance of 140 km in the southern sierra nevada california previous geologic mapping and geochronological work along the northern third of the fault indicate that dextral offset occurred sometime after 80 ma and before 3 5 ma this offset was interpreted to be the result of cenozoic basin and range extension our new results from the central third of the fault kernville lake isabella region indicate an earlier right lateral movement history contemporaneous with emplacement of the largest plutons in the sierra nevada the older structure is termed the proto kern canyon fault zone the cenozoic fault trace is a narrow zone of brittle deformation whereas the cretaceous fault zone is a broad zone of ductile deformation u pb zircon geochronology on plutonic and metavolcanic rocks involved in the ductile deformation as well as a pluton that postdates ductile deformation demonstrate that the proto kern canyon fault zone was active at 85 ma and may have begun to move as early as 105 ma longitudinal strike slip faults are common in modern magmatic arcs where convergence is oblique the proto kern canyon fault zone may have originated in response to a moderate northward component in subduction of the farallon plate or perhaps a strong northward component for the kula plate

palynomorphs of ice rafted clastic sedimentary rocks in late quaternary glacial marine sediments of the norwegian sea as provenance indicators abstract palynomorph assemblages of ice rafted pebbles of clastic sedimentary rocks in surface sediments from 0 to 41 cm depth of the norweigan sea are dominated by triassic and lower cretaceous taxa along with occasional jurassic lower paleozoic and very rare carboniferous permian taxa tertiary species were not found and upper cretaceous species were only found in the western norweigan sea the ice rafted rock fragments originated from the late pleistocene ice sheets adjacent to the norwegian sea the determined ages of the ice rafted clastic sedimentary rocks indicate the barents shelf as the main source because the barents shelf has exposures of clastic sedimentary rocks whose ages and lithologies match the material found in the majority of the analyzed samples in addition some material originated from the west norwegian shelf and some from ne greenland our results confirm that an ice sheet extending from sw svalbard onto parts of the northwestern barents shelf existed during the late weichselian the northern dropstone source areas suggest that currents in the norwegian sea from 15 to 9 ka before present were moving in the opposite direction of modern currents

low temperature thermochronology of anticosti island a case study on the application of conodont u th he thermochronology to carbonate basin analysis abstract the ordovician to silurian carbonate succession preserved on anticosti island is a near continuous record of the changing depositional and tectonic history of the early paleozoic laurentian margin these strata are a prime natural laboratory to test the applicability of conodont apatite u th he thermochronology cahe for carbonate basin analysis in a setting with a well understood burial history and abundant paleotemperature constraints we report 63 cahe dates from seven samples collected from two boreholes x ray micro computed tomography xr ct was used to assess individual conodont element size volume and alpha ejection correction cahe dates are negatively correlated with effective uranium concentration eu with single conodont dates enigmatically older than the age of deposition to conodont dates as young as 2 7 0 2 ma we rationalize this dispersion as a product of several factors including diagenetic processes and pervasive conodont crystalline porosity and permeability additionally one basement and two sandstone samples were collected for apatite and zircon u th he ahe zhe and apatite fission track aft thermochronology in the precambrian basement zhe dates range from 581 7 46 5 ma to 761 2 60 9 ma n 4 and ahe dates range from 26 7 1 6 to 48 4 2 9 ma n 4 ahe dates from two lower ordovician sandstones n 8 are positively correlated with eu increasing from 13 7 0 8 ma to 105 2 6 3 ma over a range of 186 ppm eu thermal history modeling of these data suggests two plausible thermal histories both of which are novel as they imply that far field effects related to the opening of the atlantic ocean have influenced the thermal history of anticosti island ultimately these data highlight the complexities associated with and necessity of low temperature thermochronology in carbonate basins

strain accommodation about strike slip fault discontinuities in granitic rock under brittle to ductile conditions abstract brittle and ductile structures adjacent to fault terminations and echelon fault steps of left lateral strike slip faults in the lake edison granodiorite of the central sierra nevada california are related to stress perturbations caused by fault slip the structures associated with fault terminations change from dilatant splay fractures only to splay fractures and ductile fabrics on opposing sides of the fault to ductile fabrics ahead of the fault with decreasing distance from a younger neighboring pluton and presumably with increased temperatures the distributions of deformation mechanisms correlate with the inferred local magnitudes and spatial distributions of the maximum tensile stress the mean stress and the maximum shear stress displacements along the faults are transferred across echelon stepovers by mineralized dilatant fractures in extensional steps to accommodate slip transfer across contractional steps rock apparently was squeezed vertically out of the step by ductile flow concentrations of mobile and immobile elements indicate that diffusive mass transfer was not significant increased mean stress in contractional steps apparently enhanced crystal plastic flow of quartz a flow law that includes a pressure effect through correlation with pressure dependent solidus temperatures is more successful than other experimentally derived flow laws in predicting the observed distribution of ductile fabrics

subsurface structure at the insight landing site from compliance measurements by seismic and meteorological experiments measurements of ground compliance at the insight landing site describing the surface response to pressure loading are obtained from seismic and meteorological data compliance observations show an increase with frequency indicating the presence of a stiffer rock layer beneath the exposed regolith we performed a markov chain monte carlo inversion to investigate the vertical profile of the elastic parameters down to 20 m below insight compliance was inverted both freely and assuming prior knowledge of compaction in the regolith and the limitations and strengths of the methods were assessed on the basis of theoretical considerations and synthetic tests the inverted young modulus exhibits an increase by a factor of 10 100 over the first 10 15 m compatible with a structural discontinuity between 0 7 and 7 m the proposed scheme can be used for joint inversion of other seismic geological or mechanical constraints to refine the resulting vertical section

the influence of wind on measurements of seismic noise summary the horizontal to vertical spectral ratio hvsr technique of microtremor measurement is widely applied in microzonation and site response studies given the small amplitude of the measured signal unwanted disturbances may adversely affect the results we analysed the influence of local wind on microtremor measurements as follows first we studied variation in hvsr at a permanent three component seismological station under various wind patterns second we conducted an experiment under controlled condition in a wind room equipped with a laser particle image velocimeter analysing the effect of increasing wind speed on various sensor digitizer configurations third we undertook numerical modelling to explain the observed data our main conclusions are that wind increases the amplitude of all components of the microtremor wavefield but does not affect hvsr however certain sensor digitizer configurations can be adversely affected by instrumental noise due to turbulence at the air instrument ground interface

seismic stratigraphy of the post breakup succession offshore northeast greenland links to margin uplift abstract the timing of the continental breakup between norway and greenland and the subsequent plate tectonic motions are well understood however due to the remote location of the northeast greenland shelf relatively few details about the tectonosedimentary response to the tectonism following the breakup have previously been published this article gives new insights into the structural and sedimentary history of the northeast greenland shelf with an emphasis on the post breakup tectonics using state of the art 2d seismic data the results of this study clearly shows a highly dynamic post breakup tectonic setting with pronounced kilometre scale fault offsets tilting of the danmarkshavn basin and pronounced progradational events the tectonosedimentary events are linked with the passage of the icelandic mantle plume south of the northeast greenland shelf based on tectonostratigraphic interpretations and integration of data from odp 913 this study constructs a temporally robust model for the post breakup succession significant post breakup uplift and tectonism related to thermal uplift is present on the margin it is observed that the icelandic hot spot passes relatively close by the northeast greenland shelf

observations of ambient noise and signal coherency on the island of hawaii for teleseismic studies abstract ambient seismic noise conditions at several sites on the island of hawaii have been studied by analyzing noise power spectral density psd and signal to noise ratio snr of teleseisms broadband digital waveform data used in this study were collected during project aloha direct comparison of noise psd and snr of teleseisms simultaneously recorded at stations on hawaii and at station kip on oahu indicates that the stations on hawaii are quieter than station kip on oahu in the frequency band of 0 1 to 1 hz suggesting that the island of hawaii can provide better noise conditions than station kip our interpretation of this observation is that the area and volume of hawaii are much larger than those of oahu and distances to the coast for the stations on hawaii are larger than that for station kip on oahu stronger attenuation and relatively low coherency for teleseismic signals on hawaii in frequencies of 0 4 to 1 2 hz are attributed to the presence of partial melt in the upper mantle teleseismic signal coherency is very low at frequencies above 2 hz for a small array with a radius about 2 km the relatively high coherency of the tangential component is strongly indicative of severe scattering effects caused by the heterogeneity in structure of the active volcanic area

tectonic inversion in the wandel sea basin a new structural model of kilen eastern north greenland the seminunatak kilen in eastern north greenland with its complexly deformed carboniferous cretaceous strata is a key area to understand the tectonic history of the transform plate boundary between eastern north greenland and svalbard detailed 3 d geological mapping from oblique photogrammetry along with limited ground fieldwork and interpretation of previously published data forms the basis for a new structural model of kilen previous structural models interpreted rhombic shaped fault patterns as the evidence for strike slip tectonics these structures are here interpreted to be the result of a post coniacian ne sw extension with nw se trending normal faults followed by later n s compression of presumable paleocene eocene age folding the faults passively and suggesting the presence of a basal detachment furthermore two thrust sheets have been distinguished on kilen a lower kilen thrust sheet and an upper hondal elv thrust sheet separated by a subhorizontal fault the central detachment the style of deformation and the structures described are interpreted as the result of paleocene eocene n s directed compression resulting in basin inversion with strike slip faults only having minor status this indicates that the greenland margin as exposed on kilen and the conjugate svalbard margin in the west spitsbergen fold and thrust belt are more similar than previously anticipated

magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of california effects of assimilation crustal thickness and depth of crystallization in order to better understand geologic fac tors controlling pronounced regional variations in whole rock chemistry mineralogy and mineral chemistry in the batholiths of california we calculate the magmatic intensive variables f hf f h 2 o f hf f hcl and f o 2 regional scale west to east increases in f oh in mafic silicates corresponding to the systematic i wc to i mc and i sc progression reflect orders of magnitude increase in f hf f h 2 o attending pluton crystallization low f hf f h 2 o of formation of western i wc types is consistent with their derivation from low fluorine source rocks in subducted oceanic slabs or the upper mantle in contrast higher f hf f h 2 o of crystallization of i mc and i sc types to the east implies the involvement of 1 progressively greater amounts of continental crustal source material such as biotite bearing metamorphic rocks their unweathered sedimentary derivatives retaining f rich mafic minerals or their fusion products and or 2 source materials which become more f rich toward the continental interior the regional distribution of i mc and i sc types suggests that the precambrian craton of western north america or derivative sediments may extend farther north in california and be morphologically more complex than previously thought from seemingly out of place occurrences of i wc plutons on the eastern slopes of the sierra nevada batholith we infer the existence of regions where precambrian basement was thin or absent in mesozoic time which prevented extensive cratonal contamination of subducted slab or upper mantle derived magmas new methods for estimating t f o 2 relations in the magmas demonstrate that i scr granites crystallize at oxygen fugacities as much as five orders of magnitude lower than those of i wc i mc and i sc types under conditions at or below the maximum stability limit of graphite in equilibrium with a c o h s gas phase the local scale formation of i scr granites in plutonic belts within specific wall rock terranes containing highly reducing sediments or metasediments may occur by contamination of i types with graphitic pelite or in some cases by the direct fusion of this reducing pelitic wall rock the spatial distribution of i scr granite provinces therefore is controlled simply by wall rock lithology amphibole geobarometry demonstrates a general west to east decrease in crystallization pressure across the sierra nevada batholith in contrast the peninsular ranges batholith displays a west to east crystallization pressure increase the bulk of the california batholiths crystallized at pressures less than 4 5 kb and depths less than about 15 19 km in the southern sierra nevada batholith the san gabriels and the eastern peninsular ranges however plutons crystallized at pressures exceeding 6 kb at deep crustal levels 23 km reconstruction of the pre erosion top of the batholith shows that in an east west cross section the central sierra nevada batholith was a horizontal tabular body with an aspect ratio of at least five to one

shallow elasticity structure from colocated pressure and seismic stations in the pinon flat observatory and estimation of vs30 author s tanimoto toshiro wang jiong abstract summary an algorithm developed in tanimoto a wang for deriving shallow elasticity structure from colocated pressure and seismic instruments is applied to data at nine stations in the pinon flat observatory pfo in southern california depth resolution kernels indicate that this approach can recover near surface shear modulus structure in the upper 50 100 m of the earth our estimate for vs30 at the closest station bph01 agrees with an independent result by yong et al which was based on an active source survey with a geophone array vs30 derived from the borehole s wave speed model by fletcher et al also agrees with estimates at nearby locations considering the size of uncertainties derived structures are much smoother than their models however this is because our method analyses slow quasi static deformation of the solid earth in the frequency range 0 005 0 05 hz that inherently limits depth resolution lack of detailed variations in structures does not seem to be the problem for estimating vs30 as vs30 is an averaged quantity from the upper 30 m of the earth also our estimates are not affected by different choices of frequency range in the inversion however our method may have some difficulty at stiff hard rock sites because ground deformation caused by surface pressure can become small and the key observables in our method the ratios between seismic amplitude and surface pressure change become difficult to measure accurately

pressure induced noise on horizontal seismometer and strainmeter records evaluated by finite element modelling summary barometric pressure induced noise is one of the major limiting factors in analysing longperiod seismological records especially the horizontal components are strongly affected the barometric pressure influence originates from the attraction by the air masses and deformations of the crust of the earth resulting in accelerations strain and tilts these factors are enhanced by the local topography and the installation site of the instrument although this influence is known for several years the physical transfer mechanisms are still not well understood by means of finite element fe analysis deformations caused by different pressure loadings are studied for moxa observatory the main topographic elements of the observatory surroundings like hill flanks and a valley in an area of approximately 2 5 km 2 are included in the model the gallery in which a long period sts 1 seismometer and two quartz tube strainmeters are installed is modelled with a high resolution of 5 m the fe model is exposed to three principle loading scenarios i uniform barometric pressure loading ii wind induced pressure on a hill flank and iii passages of pressure fronts as a linear elastic rheology is used the loading effects can be superimposed and scaled as necessary in order to get an estimate about the influence of cavity effects compared with that of topography the computations are redone for a model containing only the gallery but no topography additionally the influence of dipping layers and a possible cleft system on the pressure effects are studied from the fe analyses follows that all three scenarios can lead to significant tilts of approximately 0 1 to 0 7 nrad hpa 1 at the sites of the instruments this is the same order of magnitude observed in the seismometer data also the directions of the tilts are in agreement the deformation effects obtained for the strainmeters are too small by more than 1 order of magnitude a qualitative agreement between model results and observations can be found and the change in polarity occurring during the passage of a pressure front can be explained besides a direction dependence of the effects can be shown for the different components of the instruments as well as a dependence on the movement of the air masses anisotropy or a cleft system can modify the pressure influence regarding the order of magnitude up to a factor of 10 and the polarity of the effects a cleft system might be the explanation for the small effects observed in the n s component of the sts 1 seismometer

wandel sea basin a new synthesis of the late paleozoic to tertiary accumulation in north greenland the wandel sea basin in eastern north greenland is the least known of the onshore depositional centers associated with the formation of the arctic and north atlantic oceans whereas the main features of svalbard and the sverdrup basin have been known for many years it has only recently been possible to investigate the wandel sea basin in any detail in the course of recent investigations the concept of a classic bull9s eye type of accumulation in north greenland has become increasingly difficult to maintain this paper presents an alternative model involving a complex series of events with an overall change from elongate rift basins to a strike slip dominated structural belt individual events in this development provide evidence of early steps in the extended processes leading up to ocean formation

a preliminary investigation into the relationship between long period seismic noise and local fluctuations in the atmospheric pressure field summary the displacement response of an elastic half space to a plane pressure wave is examined in order to establish the conditions under which sources of this type can contribute significantly to the long period seismic noise field the study is restricted to pressure waves which propagate at velocities well below the seismic wave velocities characteristic of the half space the numerical studies indicate that pressure waves with amplitudes of 100 pbar or more can contribute significantly to the long period vertical background noise observed at the surface provided that the detectors are located on sections of alluvial fill or poorly to moderately indurated sandstones and shales whose thicknesses are greater than about a kilometre these same waves can also create significant tilt noise on long period horizontal seismographs located at or near the surface regardless of the rock type the seismic disturbances created by pressure waves decay rapidly away from the surface therefore it appears that it may be possible to eliminate the effects of atmospherically generated noise by placing the detectors at moderate depths

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

variation in slip on intersecting normal faults implications for paleostress inversion numerical models based on linear elasticity theory predict asymmetric slip distribution with a steep slip gradient near the line of intersection of intersecting normal faults they also predict a discrepancy between the direction of slip on the fault plane and the direction of resolved shear stress both variations in slip magnitude and direction are due to mechanical interaction between the faults with intersecting patterns these interactions cause local perturbations of the shear stress field acting on the plane of the adjacent fault field observations from the chimney rock area of central utah show that slickensides on normal faults cutting the navajo sandstone change rake away from the expected downdip direction as the intersection line with adjacent faults is approached the sense and magnitude of this change in orientation are similar to those computed by using the numerical models the good correspondence between field observations and theoretical results from this paper not only provides insight into the mechanics of intersecting faults but suggests that care is required when using standard inverse methods to compute paleostresses from slickenside data the slickenside orientation near intersection lines will generally not be in the direction of the remote maximum shear stress as resolved on the fault plane a parameter study of this change in orientation provides helpful results for evaluating field data prior to a paleostress analysis

the effects of the atmospheric pressure changes on seismic signals or how to improve the quality of a station seismic investigations are mainly limited by seismic noise two microbarometers have been installed in the seismic vault of two different geoscope stations one at ssb and the other at tam all vertical components and most of the horizontal components show a significant correlation with pressure in order to correct the seismic signals from the atmospheric pressure noise a transfer function between the pressure data and the seismic data is inverted results show that after correction the noise levels reached on the horizontal components are similar between the two stations and the vertical components display noise levels below the low noise model as defined by peterson 1993 this technique reduces part of the noise and allows detection of small earthquakes and a better extraction of normal modes the analysis of the lowest normal modes of the earth excited by the m s 8 2 macquarie island earthquake is given to illustrate the perspectives of the method

broadband seismic noise attenuation versus depth at the albuquerque seismological laboratory abstract seismic noise induced by atmospheric processes such as wind and pressure changes can be a major contributor to the background noise observed in many seismograph stations especially those installed at or near the surface cultural noise such as vehicle traffic or nearby buildings with air handling equipment also contributes to seismic background noise such noise sources fundamentally limit our ability to resolve earthquake generated signals many previous seismic noise versus depth studies focused separately on either high frequency 1 hz or low frequency

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

pre ocean opening compression of the northwestern atlantic margin evidence from eastern north greenland the deformation of the wandel sea basin of eastern north greenland and the west spitsbergen fold belt are the result of late cretaceous palaeocene greenland barents sea svalbard convergence following the opening of the labrador sea baffin bay opening the tertiary rocks of the wandel sea basin are undeformed while the late palaeozoic mesozoic are weakly folded and thrust faulted thrust fault movements in north greenland ceased before mid palaeocene time when the dextral motion separating greenland and svalbard began the shortening was orthogonal to the continental margin and a transpressional origin for the deformation of the wandel sea basin is not confirmed

earth motion caused by local atmospheric pressure changes summary observations have been made of the local atmospheric pressure field and the long period seismic noise fields both on the surface of the earth and in a mine at a depth of 183 metres the observations show that during windy intervals and in the period range 20 100 s there is a strong correlation between local atmospheric pressure changes and the noise recorded by a vertical seismograph located on the surface in contrast over the same range of periods there is no correlation between the seismic noise recorded in the mine and local atmospheric pressure changes except during the passage of acoustic waves it is shown that the noise in this pass band is not due to the buoyant response of the seismograph but is caused by the motion of the earth responding to atmospheric pressure changes

the origin of the west spitsbergen fold belt from geological constraints and plate kinematics implications for the arctic abstract the west spitsbergen fold belt which extends for 300 km along the western margin of svalbard and is up to 80 km wide has much in common with foreland fold and thrust belts the near foreland segment of the fold belt exhibits ramp flat thrust trajectories whilst structurally higher nappes are typified by more listric thrusts higher nappes to the west contain imbricated carboniferous and basement rocks showing that the latter were actively involved in the fold belt deformation and a minimum of 80 km total shortening perpendicular to the western margin of svalbard is estimated the early stages of the eurekan deformation in north greenland can be linked to that of the west spitsbergen fold belt and the combined shortening across the two fold belts may exceed 80 km in ellesmere island eurekan structures are distributed in an arc like belt which records between 50 to 100 km of shortening since the late cretaceous kinematic reconstructions suggest that before the opening of the eurasian basin and norwegian greenland sea chron 25 svalbard was linked to north america in the late cretaceous palaeocene interval the motion across the greenland svalbard margin was mainly convergent giving rise to the west spitsbergen fold belt and the eurekan structures of north greenland the dextral separation of greenland and svalbard in post chron 24 time was accompanied by extension followed by pure extension in post chron 13 time

timing and nature of magmatic fabrics from structural relations around stoped blocks abstract structural relations around several large 100 m stoped blocks in the granodiorite of castle creek sierra nevada california suggest that magmatic fabrics formed as or after the space making phase of pluton emplacement had ended the stoped granite blocks are approximately 360 m below the exposed pluton roof magmatic foliations in granodiorite surrounding the blocks commonly follow km scale orientation trends to within 1 m of block contacts where they become deflected parallel to the block boundaries locally undeflected foliations occur within a few centimeters of block contacts mafic enclave fabric ellipsoid intensities 0 2 we draw the following conclusions concerning magmatic fabrics in the granodiorite of castle creek 1 magmatic fabrics formed during and or after the latest stages of pluton emplacement and thus contain little or no information about space making processes 2 magmatic fabrics had poor strain memory and 3 during magmatic fabric formation pluton strains were partially decoupled from host rock strains published data from other plutons indicate that these relationships may be common particularly in the brittle upper crust it follows from these conclusions that even in the best case magmatic fabrics contain only qualitative information about pluton emplacement mechanisms regional tectonics and internal magma chamber processes interpretations of magmatic fabrics must be corroborated by evaluating causes kinematics and magnitudes of syn emplacement host rock deformation in the worst case the causes of magmatic fabrics cannot be uniquely determined

conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides kronprins christian land lies at the northernmost limit of the east greenland caledonides and may be divided into four main tracts foreland parautochthon thin skinned thrust sheets containing neoproterozoic sediments and thick skinned thrust sheets of crystalline basement the eastern part of the foreland and the parautochthon are composed of ordovician silurian shelf carbonates overlain by llandovery lower wenlock turbidites deposited at the southern margin of the franklinian basin deformation of the parautochthon occurred beneath a major detachment the vandredalen thrust with neoproterozoic sediments of the rivieradal group lying in the hanging wall the rivieradal group was deposited in an e facing half graben and was displaced westwards across its rift shoulders during caledonian thrusting extensive sampling for conodonts has been carried out within the lower palaeozoic rocks of the foreland and parautochthon in order to increase the precision of structural interpretations and to provide data on maximum burial temperature and in turn the thickness of overburden in contrast to earlier studies conodont colour alteration indices cai show a gradual and continuous increase from cai 3 in the eastern part of the foreland to cai 5 in the easternmost parts of the parautochthon the isopleths are not disrupted or truncated by thrusting as previously suspected indicating that the heating is not attributable to pre thrusting stratigraphic overburden furthermore considerations of the regional geology indicate that there was no significant accumulation of sedimentary overburden in post caledonian time the predominant component is thus considered to be loading by thrust sheets modelling of the overburden thickness suggests that prior to erosion it increased from 3 9 km cai 3 in the easternmost foreland to a maximum of 12 5 km beneath the vandredalen thrust sheet in the easternmost part of the area providing constraints for restoring cross sections across the orogen

late cretaceous age of fractures in the sierra nevada batholith california regional sets of steeply dipping joints and faults are common throughout the sierra nevada batholith yet relatively little is known about how or when they formed within some east northeast striking left lateral fault zones in the mount abbot quadrangle of the central sierra nevada the host granodiorite is hydrothermally altered to a lower greenschist assemblage that contains muscovite the muscovite yields a mean k ar and sup 40 ar sup 39 ar age of 79 ma which provides a minimum age for the faulting field relations show that these faults developed from earlier formed mineralized joints so these ages also provide a minimum age for the jointing published ages of biotite hornblende and zircon from the host granodiorite of lake edison are 80 ma k ar 85 ma k ar and 90 ma u pb respectively the geochronology field relations and hydrothermal mineral assemblages together suggest that the mineralized joints and faults all formed between 85 and 79 ma soon after the host pluton was emplaced

state of stress and tectonic evolution of the west spitsbergen fold belt abstract the west spitsbergen fold belt is the result of a e w to ene wsw oriented compression which affected the whole of spitsbergen a late cretaceous palaeocene age for the fold belt deformation is indicated by the involvement of only the basal tertiary conglomerates in the folding and thrusting in western spitsbergen this compressional event was followed by a strike slip stress pattern with nw se oriented extension and ne sw compression which generated micro structures within the tertiary rocks on the map scale normal faults produced by a ne sw oriented extension overprint the compressional structures the later strike slip and extensional stress patterns correspond to the svalbard greenland dextral motion along the de geer zone in latest palaeocene eocene time the latest tectonic event which affected the whole of svalbard was an e w oriented extension related to the spreading along the knipovich ridge in oligocene neogene time

the influence of topographic and lithologic features on horizontal deformations summary a number of studies have been carried out in order to determine the magnitude of effects originating from the surroundings of an observation site which influence seismometer records or deformation observations with tilt or strainmeters the investigations generally comprise thermal atmospheric topographic and cavity effects as well as ocean loading recently these studies have been continued and extended using finite element fe modeling the effects are investigated exemplarily using air pressure variations as loading signal the observatory sites differ in their local surroundings based on this the influence on topographic and lithologic features is investigated with respect to air pressure changes the models developed reflect different topographies around stations wide and narrow valleys hill flanks and flat areas at the foot of the hill flank galleries are integrated into the models the topographic and the gallery geometry influence are systematically investigated with regard to e g rock coverage above an observation site changes in the hill slope width of a valley and lithology the deformations are only caused by air pressure changes and not associated with gravity changes due to an advancing pressure front for loading different air pressure scenarios are simulated with an uniform load and a pressure front which moves over the model in different directions as an elastic rheology is considered the effects can be scaled to actual occurring air pressure variations initial studies focus on the cavity effect to estimate the order of magnitude to separate the pure cavity effect from other influences studies of topographic effects e g an increasing slope angle yield a non linear increase in the strain component with amplitudes up to 2 nstrain and tilt changes up to 2 nrad for a uniform air pressure load of 1 hpa for prem parameterized models different lithologies can result in five times larger deformations for moving high pressure areas changes emerge in strain of up to 2 nstrain and in tilt of up to 4 2 nrad the results obtained improve the interpretation of deformations observed with regard to fundamental geodynamic processes and contribute to the selection of future observation sites

watching the wind seismic data contamination at long periods due to atmospheric pressure field induced tilting abstract following the installation of a new broadband seismic station near the pacific coast of the olympic peninsula washington the pacific northwest seismic network recorded elevated background seismic noise at periods exceeding 30 s we observed power spectral density variations of about 15 20 db in the horizontal component seismograms between times of high and low noise and differences of up to about 25 db between the horizontal and vertical components during noisy intervals the amplitude of the signal at long periods exhibited clear correlations with cyclic daytime fluctuations of air temperature and wind speed our observations provided measurable evidence that the variations of the local atmospheric pressure field associated with local wind systems represents an effective source of ground displacements and rotations the rotational component of the pressure field induced motion is recorded by horizontal component seismometers that below their low frequency corner are sensitive to surface tilts the response of seismometers to ground rotations is characterized by a transfer function which we use to estimate the amplitude of tilt we measured a pressure field induced surface tilt of the order of several tenths of rad based on simple modeling tilt contamination is expected to attenuate rapidly with depth and to become negligible just a few hundreds of meters below the surface removal of this unwanted effect from seismograms remains a challenging task as the details of tilting depend on the nonstationary character of the pressure field the compliance of the near surface to pressure variations and the design and construction of the seismic station online material animated time sequenced plots of daily seismic noise pdfs

formation and growth of extensional fracture sets naturally occurring extension fractures including some joints and veins form sets consisting of numerous subparallel fractures each with well defined ends in order to correctly interpret these fractures in the field it is necessary to determine which factors control the geometries of fracture sets this requires consideration of the conditions leading to both the initiation and the cessation of fracture propagation a fracture begins to propagate when the crack extension force reaches a critical value which is a property of the rock and of environmental conditions after propagation initiates the crack extension force varies owing to 1 increase in crack length 2 change in remote strain 3 elastic interaction with nearby cracks 4 change in internal fluid pressure and 5 stress relaxation due to growth of cracks in the surrounding rock each fracture continues to propagate as long as its crack extension force exceeds the critical value and terminates when this condition is no longer met neglecting fluid effects the final geometry of the fracture set is a function of the remote strain history and the initial crack geometry which can be characterized by the initial crack density for low initial densities large increases in crack length occur with little or no increase in remote strain however for large initial densities crack lengths increase only if the applied strain increases this analysis is used to estimate the variation in remote strain during formation of a fracture set in granitic rock from observations of the final fracture geometry

formation of joints in cooling plutons abstract the geometry age and mineralogy of steeply dipping joints in the lake edison granodiorite of california indicate that thermal stresses played a key role in the formation of the joints joint traces curve to approach the pluton boundary at high angles at both large and small scales and they generally terminate at or near the contact with an older pluton radiometric dates and the epidote and chlorite fillings of the joints tie jointing to the initial cooling of the pluton a thermo mechanical stress analysis assuming two dimensional conductive cooling predicts thermal stresses of several tens of mpa the same order of magnitude as plausible fluid pressures regional stresses and lateral normal stresses associated with the overburden the orientation of the joints can be accounted for rather well by the stress field formed by superposing a uniform regional stress field on the predicted thermal stresses the large scale pattern of the early joints in many plutons should be predictable based on a pluton s geometry its age relative to the adjacent rock and knowledge of the regional stress at the time of initial cooling these findings bear on issues pertinent to mining petroleum recovery nuclear waste repository siting and ground water flow