review of magnetic and electric field effects near active faults and volcanoes in the u s a abstract synchronized measurements of geomagnetic field have been recorded along 800 km of the san andreas fault and in the long valley caldera since 1974 and during eruptions on mount st helens since 1980 for shorter periods of time continuous measurements of geoelectric field measurements have been made on mount st helens and near the san andreas fault where moderate seismicity and fault slip frequently occurs significant tectonic and volcanic events for which nearby magnetic and electric field data have been obtained include 1 two moderate earthquakes m l 5 8 for which magnetometers were close enough to expect observable signals about three source lengths 2 one moderate earthquake m s 7 3 for which magnetometers were installed as massive fluid outflow occurred during the post seismic phase 3 numerous fault creep events and moderate seismicity 4 a major explosive volcanic eruption and numerous minor extrusive eruptions and 5 an episode of aseismic uplift for one of the two earthquakes with m l 5 8 seismomagnetic effects of 1 3 and 0 3 nt were observed for this event magnetometers were optimally located near the epicenter and the observations obtained are consistent with simple seismomagnetic models of the event similar models for the other event indicate that the expected seismomagnetic effects are below the signal resolution of the nearest magnetometer precursive tectonomagnetic effects were recorded on two independent instruments at distances of 30 and 50 km from a m l 5 2 earthquake longer term changes were recorded in one region in southern california where a moderate m l 5 9 earthquake has since occurred surface observations of fault creep events have no associated magnetic or electrical signature above the present measurement precision 0 25 nt and 0 01 respectively and are consistent with near surface fault failure models of these events longer term creep is sometimes associated with corresponding longer term magnetic field perturbations correlated changes in gravity magnetic field areal strain and uplift occurred during episodes of aseismic deformation in southern california primarily between 1979 and 1983 because the relationships between these parameters agrees with those calculated from simple deformation and tectonomagnetic models the preferred explanation appeals to short term strain episodes independently detected in each data set an unknown source of meteorologically generated noise in the strain gravity and uplift data and an unknown but correlated disturbance in the absolute magnetic data might also explain the data no clear observations of seismoelectric or tectonoelectric effects have yet been reported the eruption of mount st helens generated large oscillatory fields and 9 2 nt offset on the only surviving magnetometer a large scale traveling magnetic disturbance passed through the san andreas array from 1 to 2 h after the eruption subsequent extrusive eruptions generated small precursory magnetic changes in some cases these data are consistent with a simple volcanomagnetic model magneto gas dynamic effects and a blast excited traveling ionospheric disturbance traveling ionospheric disturbances tids also generated by earthquake related atmospheric pressure waves may explain many electromagnetic disturbances apparently associated with earthquakes local near fault magnetic field transients rarely exceed a few nt at periods of a few minutes and longer

electric and magnetic field changes observed during a seismic swarm in pollino area southern italy abstract over the last few years seismic activity in the pollino area a sector of the calabro lucanian apennines in southern italy known as a seismic gap has been very weak however in 2011 the seismicity gradually intensified culminating in an earthquake of m w 5 0 occurred on 25 october 2012 the depth of the 2011 2012 earthquake hypocenters ranges between 2 and 10 km the seismicity results in two separate clusters and traces a north northwest south southeast fracture more evident in the western sector in this area an mt station was installed on 26 september 2012 by the institute of methodologies for environmental analysis national research council of italy imaa cnr italy at about 50 km from another mt station operating since 2003 in the agri valley tramutola southern italy such a seismic swarm occurred in the pollino area more than 3600 events in last two years with local magnitude m l 0 1 it has provided a rare opportunity to study the earthquake related temporal patterns of electromagnetic em signals and is potentially informative about ongoing seismogenic processes in this study we present several cases of em field variations associated with the passage of seismic waves the maximum amplitude of the electrical signals registered at the two mt sites and the earthquake magnitude are related by an attenuation factor that depends on the distance between the hypocenter and the mt station furthermore at the two mt sites the maximum electrical anomalies seem to be more appreciable predominantly in different directions indicating a certain directivity in the propagation of the electric field a deep analysis of em time series recorded during the mainshock m w 5 0 was performed in particular by applying time frequency misfit criteria based on the continuous wavelet transform we compared the electric field with seismic recordings and we found a good waveform similarity between signals moreover we also found an em signal that significantly anticipates the theoretical first p wave arrival at the tramutola mt station

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

magnetotelluric monitoring of a fluid injection example from an enhanced geothermal system 1 enhanced geothermal systems egs are on the verge of becoming commercially viable for power production where advancements in subsurface characterization are imperative to develop egs into a competitive industry theory of an egs is simple pump fluids into thermally enhanced lithology and extract the hot fluids to produce energy one significant complication in egs development is estimating where injected fluids flow in the subsurface micro seismic surveys can provide information about where fractures opened but not fracture connectivity nor fluid inclusion electromagnetic methods are sensitive to conductivity contrasts and can be used as a supplementary tool to delineate reservoir boundaries in july 2011 an injection test for a 3 6 km deep egs at paralana south australia was continuously monitored by both micro seismic and magnetotellurics mt presented are the first results from continuous mt measurements suggesting transient variations in subsurface conductivity structure generated from the introduction of fluids at depth can be measured furthermore phase tensor representation of the time dependent mt response suggests fluids migrated in a ne direction from the injection well results from this experiment supports the extension of mt to a monitoring tool for not only egs but other hydraulic stimulations

mechanics of formation of the gold bearing quartz fuchsite vein at the dome mine timmins area ontario the highest grade orebody in the dome mine is a steeply dipping 500 m long 550 m high and 3 5 m wide banded quartz fuchsite vein qfv accompanied by subsidiary veins in the adjacent wall rock t

beach cusp morphodynamics detailed measurements of three dimensional beach cusp morphology were made on a steep gradient low energy microtidal beach in perth western australia during the field campaign a variety of wave conditions and tidal ranges were experienced and these differing hydrodynamic conditions were reflected in a consistent pattern of morphological changes to the beach cusp system a useful parameter to delineate between trends of cusp destruction and re formation appeared to be the surf similarity parameter tan i0 l0 where h0 is offshore wave height l0 is deep water wave length and tan is beach gradient for 1 2 a small storm was experienced at the start of the field campaign period and resulted in considerable erosion of the beach face the cusp morphology across the lower beachface was destroyed but a subtle remnant of the pre storm cusp morphology was preserved on the upper beachface when cusps reformed after the storm under the influence of declining wave conditions they appeared at the same location and with the same dimensions as the pre storm cusp morphology hence it is considered that the cusp re formation was controlled more by the antecedent morphology than the hydrodynamic conditions this indicates that positive feedback between swash hydrodynamics and beachface morphology necessary to form beach cusps does not require a large variation in relief 1997 john wiley sons ltd

the 2004 parkfield earthquake test of the electromagnetic precursor hypothesis 1 a controversy has existed for 30 years concerning the possibility of earthquake prediction using electromagnetic precursors long term electromagnetic monitoring prior to during and after the m6 0 earthquake at parkfield california on 28 september 2004 now provides a definitive test of this hypothesis during the earthquake our instruments recorded clearly documented electrical signals from an earthquake impulsive changes of up to 2 5 mv at an electrode located 250 m from the rupture zone followed by a transient decay lasting at least 3 1 4 hours similar signals 1 5 mv were recorded with the only two m 5 aftershocks but their transient decays lasted for only 17 min these signals are unambiguously a result of the earthquake and can be useful in studies of fluid flow in faults a major current topic in earthquake physics patterns in the distribution of transient voltages differ from static stress changes but are consistent with a small coseismic pressure drop on the fault and fluid flow inward signals at a distance of 1 km from the fault are less than 1 mv and are statistically no different from zero in our analysis transient voltages for the aftershocks have opposite polarity from those recorded with the main shock and are again maximal close to the fault suggesting subsequent outward flow from the fault finally there is no evidence of any precursory signal strongly calling into question previously suggested signals preceding smaller or more distant earthquakes

rate and mechanism in prograde metamorphism for a given rate of heat input into a prograde metamorphic sequence the extent of overstep of reaction temperature disequilibrium depends on the slowest of three sequential steps a surface detachment of reactant minerals b transport of material to the site of mineral growth and c nucleation and growth of the product mineral we have developed analytical expressions which enable determination of the rates of mineral dissolution and growth and of advective and diffusive mass transport during metamorphism the dissolution and growth steps are linear functions of the driving force g of the overall reaction while diffusion may take place either through a grain boundary fluid film or through the disorganized grain boundary itself

time lapse magnetotelluric monitoring of an enhanced geothermal system abstractrealization of enhanced geothermal systems egss prescribes the need for novel methods to monitor subsurface fracture connectivity and fluid distribution magnetotellurics mt is a passive electromagnetic em method sensitive to electrical conductivity contrasts as a function of depth specifically hot saline fluids in a resistive porous media in july 2011 an egs fluid injection at 3 6 km depth near paralana south australia was monitored by comparing repeated mt surveys before and after hydraulic stimulation an observable coherent change above measurement error in the mt response was present and causal in that variations in phase predict variations in apparent resistivity phase tensor residuals proved the most useful representation for characterizing alterations in subsurface resistivity structure whereas resistivity tensor residuals aided in determining the sign and amplitude of resistivity variations these two tensor representations of the residual mt response suggested fluids migrat

the origin of swash cusps on beaches abstract genetically there are two types of beach cusps those formed in the surfzone by the nearshore circulation system and those formed on the beachface by the swash and backwash the latter are here called swash cusps and a simple model relating the physical dimensions of swash cusps to the properties of the incident wave field and the mean beach slope is developed as in some previous models the cusp wavelength is controlled by the longshore wavelength of edge waves but the edge waves are now required only to provide small periodic perturbations on an originally uniform beach further cusp growth occurs because of the interactions between the incident waves and the perturbed topography the maximum cusp height apex to valley is hypothesized to be proportional to the significant vertical excursion of swash motions it follows from the above assumptions that the maximum possible cusp steepness cusp height cusp longshore wavelength is proportional to the mean on offshore beach slope this result agrees with field data and the value of the ratio of maximum cusp height to beach slope differs from that obtained theoretically by guza and bowen 1981 using a complicated non linear model with rather different physics the present model implies that edge waves although necessary for initiating the initial bedform perturbation need not persist for the development of mature cusp topography

saddle reef auriferous veins in a conical fold termination oldham anticline meguma terrane nova scotia canada reconciliation of structural and age data many auriferous veins dated at 370 ma in the meguma terrane of nova scotia are concentrated in tight domes and conical fold hinges that are transected by 378 ma low pressure and high temperature metamorphic isograds and 380 370 ma granitoid plutons published experiments suggest that such folds are diachronous initiating at inhomogeneities and propagating both in amplitude and along their length thus fold terminations are typically conical in geometry and record only the youngest increment of folding the northeastern termination of the oldham anticline is characterized by 1 a conical fold 2 saddle reef auriferous veins 3 divergent and convergent cleavage fans 4 a downdip lineation on the slaty cleavage defined by biotitic mineral aggregates inferred to have developed during fold growth the age of the biotitic mineral aggregates is bracketed between peak metamorphism at 600 c defined by a nearly concordant 378 ma u pb monazite age from a xenolith in lamprophyre dyke and 366 ma 40 ar 39 ar muscovite biotite ages recording cooling through 400 300 c this suggests that the conical termination of the oldham anticline grew between 378 and 366 ma an observation that reconciles the empirical structural control of the saddle reef auriferous veins with the 370 ma age dating of vein minerals application of this conclusion to saddle reef auriferous veins in domes suggests that mineralization was related to the youngest increment of fold amplification

sediment slump structures a review of diagnostic criteria and application to an example from newfoundland abstract in the study of the history of deformed sedimentary rocks it is important that the cause of the deformation and the timing of deformation relative to metamorphic and tectonic events be assessed there is a continuous gradation between the deformation of freshly deposited sediments by gravitational forces and the deformation of well lithified sediments by tectonic forces so determining the degree to which gravity tectonism and lithification influenced deformation can be very difficult the characteristics that may be considered in determining the origin of deformational structures in sedimentary rocks can be divided into five categories ductile deformation structures 1 can provide definitive criteria for recognizing post lithification deformation but not pre lithification deformation this also holds for 2 brittle deformation structures and decollements overprinting of sediment reworking or remobilization structures 3 are the best criteria for recognizing pre lithification structures fabrics 4 can be very useful but are as yet poorly understood and there are misconceptions in the literature about what sort of fabrics are or are not found in unlithified sediments spatial relationships 5 may also tell us a great deal but are most useful when taken in conjunction with other types of evidence complex fold patterns in sandstones on farmer head north central newfoundland provide a case study for criteria that may be used to determine the degree of lithification during deformation although these folds have been interpreted as slump folds by earlier workers fabrics and spatial relationships point to a tectonic post lithification origin for the structures a conclusion which has significant implications for the interpretation of the regional geology

a review of the mesothermal gold deposits of the meguma group nova scotia canada abstract the gold province of the meguma terrane in nova scotia contains several classic examples of turbidite hosted mesothermal gold deposits there are over 300 gold occurrences and deposits hosted by the cambro ordovician meguma group rocks in southern nova scotia canada the meguma group consists of two formations 1 a lower sand dominated flysch goldenville formation and 2 an upper shaley flysch halifax formation subdivision of the goldenville formation into several map units is leading to a better understanding of the stratigraphic constraints on the gold mineralization although detailed stratigraphic investigations in all of the major gold producing areas is still ongoing it is evident that the steve s road beaverbank and the mt uniacke stratigraphic intervals contain most of the major past gold producers in the province the meguma group rocks are variably deformed into upright gently to moderately doubly plunging folds with multiple cleavages the strata are metamorphosed from greenschist to amphibolite facies and are subsequently intruded by ca 370 ma peraluminous granites and minor mafic intrusions the gold deposits can be divided into three main types 1 high grade approximately 15 g t au narrow gold bearing quartz veins 2 low grade 0 5 4 g t au slate argillite hosted and 3 low grade meta sandstone hosted a combination of two or more of the above can also occur almost all of the historic production 47 million g au has come from the high grade veins within 200 m of surface a variety of vein types occur although most of the gold produced came from bedding concordant stockwork and fissure veins isotopic investigations and dating of the vein minerals indicate that the mineralization was related to migration of metamorphic fluids from multiple reservoirs in the waning stages of the acadian orogeny disseminated low grade gold with minor electrum and associated intermetallic compounds and metal alloys have recently been recognized in host rocks at several of the former gold mining areas in nova scotia the presence of disseminated gold in combination with high grade vein mineralization greatly enhances the economic viability of gold deposits in the meguma group the association of disseminated gold and narrow vein hosted deposits has important exploration implications for similar mesothermal gold districts elsewhere

fracture networks in frozen ground fractures in frozen ground self organize into networks through interactions between sequentially emplaced fractures tensile stress and the developing fracture pattern from this viewpoint we model the development of networks on a lattice representing the ground surface on which fractures initiate propagate and arrest under a combination of uniform thermally induced tensile stress stress reduction near existing fractures and stochastic parameterization of heterogeneity in frozen ground and in insulating snow tensile stress from cooling tensile strength propagation threshold fracture depth and elastic properties are chosen to approximate properties of frozen ground using these parameters model networks assemble with properties similar to natural ice wedge networks including 1 individual fracture paths have lengths ranging from tens to hundreds of meters 2 fractures intersect to enclose regions with characteristic spacing between fractures of approximately 22 m 3 intersections between fractures are predominantly orthogonal with less common three way approximately equiangular intersections joint distributions of relative orientation and spacing between fractures from modeled networks and ice wedge networks at espenberg alaska are comparable at the level of variability in natural examples this similarity is consistent with the hypotheses that networks self organize by stress interactions between sequentially placed fractures in frozen ground and that networks are insensitive to the many details of fracture dynamics omitted from the model spacing between fractures in modeled networks is influenced by sub optimal placement of fractures during network development and increases nonlinearly with the length scale of stress reduction around a fracture three way approximately equiangular intersections form where modeled fractures arrest on the outside of bends in earlier fractures

morphological evolution of beach cusps and associated swash circulation patterns abstract a numerical model capable of simulating the motion of water particles on beach cusp morphology under the influence of an initial velocity and gravity is presented the model indicates that the typical swash pattern on beach cusps is three dimensional with wave uprush diverging at the cusp horns resulting in concentrated backwash streams in the embayment the degree of horn divergence is an increasing function of the parameter e s 2 where e quantifies the prominence of the beach cusps s is the horizontal swash excursion length and is the cusp spacing the numerical experiments are supplemented with detailed field measurements of beach cusp morphological change the field data include three types of morphological response each characterised by a particular pattern of swash circulation that can be delineated using e s 2 when e s 2 beach cusp morphology is large and or subdued in relation to the swash length swash circulation is essentially two dimensional oscillatory flow and results in steepening of the beachface and infilling of the cusp embayments for e s 2 0 015 to 0 15 wave uprush is deflected from the cusp horns and flows into the embayments where it exits in a concentrated backwash stream horn divergent flow the ensuing swash backwash inequality reinforces cusp development and maintains existing cusp morphology when e s 2 0 15 beach cusps are small and or pronounced in relation to the length of the swash overtopping and ponding of the cusp horn takes place and swash circulation is from the embayment to the horn horn convergent flow as a result cusp horns are eroded and accretion occurs in the embayments

field observations of beach cusps and swash motions abstract we tested the hypothesis of cusp formation by the longshore structure of synchronous or subharmonic mode zero edge waves using detailed field measurements of foreshore topography incident waves and swash motions two distinct intervals of cusp formation were observed alongshore separated swash measurements were analyzed to detect structures at wavelengths and frequencies consistent with the measured cusp spacings for both events no statistical support for cusp generation by the traditional subharmonic or synchronous edge wave mechanisms was found however once cusps became well developed there was evidence of interaction between fluids and topography at a wavelength equal to the cusp spacing but at the period of the incident swash we propose that this interaction could have been responsible for the generation of the second set of cusps with a spacing of half the pre existing cusp wavelength

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

shear sense indicators in striped bedding veins striped bedding veins are veins that lie subparallel to bedding and have an internal layering or lineation at a small angle to the veins long axis they form during bedding parallel slip and can be used as shear sense indicators solid inclusion trails produce the visible internal layering or lineation and track the opening direction of the veins elongate quartz crystals however can be oriented at an angle of up to 80 to the opening direction are non tracking and contain almost no information on the shear sense the striped bedding veins can be separated into three types according to the geometry of their internal segmentation veins of type b opened parallel to jogs oriented at a low angle to bedding veins of type j opened parallel to jogs oriented at a high angle to bedding and veins of type o opened orthogonal to bedding and jogs striped bedding veins of types b and j contain crack seal inclusion bands and displacement parallel inclusion trails striped bedding veins of type o feature only crack seal inclusion bands the example of striped bedding veins presented in this paper from the orobic alps of italy belongs to type b the lineation in the veins and the orientation of the inclusion bands and inclusion trails as well as the orientation of steps in the vein wall can be used to determine the sense of shear and the direction and amount of vein opening or bedding parallel slip

statistical analysis of ulf seismomagnetic phenomena at kakioka japan during 2001 2010 to clarify and verify the ultralow frequency ulf seismomagnetic phenomena we have performed statistical studies on the geomagnetic data observed at the kakioka kak station japan during 2001 2010 we investigated the energy of ulf geomagnetic signals of the frequency around 0 01 hz using wavelet transform analysis to minimize the influences of artificial noises and global geomagnetic perturbations we used only the geomagnetic data observed at nighttime lt 2 30 a m to 4 00 a m and utilized observations from a remote station kanoya as a reference statistical results of superposed epoch analysis have indicated that ulf magnetic anomalies are more likely to appear before sizable earthquake events es 108 rather than after them especially 6 15 days before the events further statistical investigations show clearly that the ulf geomagnetic anomalies at kak station are more sensitive to larger and closer events finally we have evaluated the precursory information of ulf geomagnetic signals for local sizable earthquakes using molchan s error diagram the probability gain is around 1 6 against a poisson model the above results have indicated that the ulf seismomagnetic phenomena at kak clearly contain precursory information and have a possibility of improving the forecasting of large earthquakes

water contents of silicic to intermediate magmas silicic to intermediate magmas have water contents that range from 1 wt to around 7 wt depending on the character and depth of the magma source type of melting reaction and the degree of differentiation the condition of water saturation is rare implying that crustal magma genesis generally takes place under fluid absent conditions or that any fluid present must contain volatile species other than h2o the source and quantity of water present during partial melting profoundly affect the types of melting reactions residues and magmas as well as subsequent magma evolution for s type granitic magmas melting reactions involving muscovite breakdown in pelites yield low temperature wet melts that form veins pockets and small plutons in regional metamorphic terranes biotite breakdown in pelites near the amphibolite granulite facies transition yields hotter magmas with variable water contents these are emplaced at medium to high levels under granulite facies conditions biotite breakdown in quartzofeld spathic rocks yields high temperature dry magmas emplaced as subvolcanic batholiths and volcanics

volume loss during cleavage formation in the meguma group nova scotia canada abstract diffusive mass transfer pressure solution is a widely recognized cleavage forming mechanism under low grade conditions the amount of accompanying volume change during cleavage development however is difficult to quantify and remains controversial the distance between sites of mineral dissolution and reprecipitation and transport mechanisms also are controversial the structural history of the cambrian ordovician meguma group nova scotia canada is well known and abundant strain markers provide an opportunity to assess geometrically volume changes accompanying cleavage development during diagenesis about 70 compaction in muds and 15 in silts and sands occurred the pelitic to psammitic meguma group was cleaved prior to being folded pressure solution was the dominant cleavage forming deformation mechanism under chlorite grade metamorphic conditions during the early devonian acadian orogeny measurement of tectonic strain in principal directions x y z shows that bedding parallel coaxial shortening z is 60 and there is no evidence of fold hinge parallel extension y estimation of tectonic vertical extension x in the cleavage plane is complicated by diagenetic compaction corrections to primary strain markers but is insufficient to compensate for the observed 60 shortening in z indicating 40 60 volume loss during cleavage formation because cleavage formed at least 50 ma after deposition and under approximately 6 km of silurian to early devonian strata porosity of the sediments upon onset of cleavage was likely less than 15 pore space reduction therefore cannot account for the apparent volume loss during cleavage formation cleavage related volume loss applies regionally and to a stratigraphic thickness of several thousand meters implying that a large amount of material was removed and transported large distances when combined with 50 shortening by folding a bulk tectonic shortening of 80 is estimated for the meguma group during the acadian orogeny

mechanics of formation of gold bearing quartz veins nova scotia canada comment discussion sur l article de mawer c k 1987 mechanics of formation of gold bearing quartz veins nova scotia canada tectonophysics 135 pp 99 119

probabilistic 3 d time lapse inversion of magnetotelluric data application to an enhanced geothermal system summary surface based monitoring of mass transfer caused by injections and extractions in deep boreholes is crucial to maximize oil gas and geothermal production inductive electromagnetic methods such as magnetotellurics are appealing for these applications due to their large penetration depths and sensitivity to changes in fluid conductivity and fracture connectivity in this work we propose a 3 d markov chain monte carlo inversion of time lapse magnetotelluric data to image mass transfer following a saline fluid injection the inversion estimates the posterior probability density function of the resulting plume and thereby quantifies model uncertainty to decrease computation times we base the parametrization on a reduced legendre moment decomposition of the plume a synthetic test shows that our methodology is effective when the electrical resistivity structure prior to the injection is well known the centre of mass and spread of the plume are well retrieved we then apply our inversion strategy to an injection experiment in an enhanced geothermal system at paralana south australia and compare it to a 3 d deterministic time lapse inversion the latter retrieves resistivity changes that are more shallow than the actual injection interval whereas the probabilistic inversion retrieves plumes that are located at the correct depths and oriented in a preferential north south direction to explain the time lapse data the inversion requires unrealistically large resistivity changes with respect to the base model we suggest that this is partly explained by unaccounted subsurface heterogeneities in the base model from which time lapse changes are inferred

informational analysis of apparent earth s resistivity time series to assess the reliability of magnetotelluric measurements abstract we used the informational methods of the shannon entropy power and the fisher information measure to analyze the time dynamics of one year of semi daily values of apparent resistivity calculated on the base of the magnetotelluric mt monitoring at penghu island taiwan the performed statistics indicate that the day time measurements present higher disorder and lower organization than the night time measurements such difference is more evident for the high frequency band of resistivity data which suggests that possibly some source of the electromagnetic field could be of anthropic origin furthermore we also note the characteristics of so called mt dead band with the periodicity of 10 s could be revealed in the high values of shannon entropy power

beach cusp destruction formation and evolution during and subsequent to an extratropical storm duck north carolina many studies have debated whether beach cusps are erosional or depositional features the april 12 14 1988 extratropical storm provided an opportunity to view the direct effects of one of the largest storms of the past decade upon beach sedimentology and morphology on barrier islands near duck north carolina prior to the storm the beach at duck was characterized by a well defined pattern of beach cusps with horn to horn spacings averaging 35 m storm induced alterations were dominated by an initial period of beach erosion that remobilized the upper 30 to 50 cm of beach sediment followed by aggradation net aggradation was most prominent along the middle beachface and within the pre storm cusp bays these morphologic adjustments resulted in the destruction of cusps which were replaced with a post storm planar beachface composed of horizontally bedded fine to coarse grained sediments within 24 hrs of storm subsidence new beach cusps formed sequentially along the coast in the direction of longshore

test of self organization in beach cusp formation 1 field observations of swash flow patterns and morphology change are consistent with the hypothesis that beach cusps form by self organization wherein positive feedback between swash flow and developing morphology causes initial development of the pattern and negative feedback owing to circulation of flow within beach cusp bays causes pattern stabilization the self organization hypothesis is tested using measurements from three experiments on a barrier island beach in north carolina beach cusps developed after the beach was smoothed by a storm and after existing beach cusps were smoothed by a bulldozer swash front motions were recorded on video during daylight hours and morphology was measured by surveying at 3 4 hour intervals three signatures of self organization were observed in all experiments first time lags between swash front motions in beach cusp bays and horns increase with increasing relief representing the effect of morphology on flow second differential erosion between bays and horns initially increases with increasing time lag representing the effect of flow on morphology change because positive feedback causes growth of beach cusps third after initial growth differential erosion decreases with increasing time lag representing the onset of negative feedback that stabilizes beach cusps a numerical model based on self organization initialized with measured morphology and alongshore uniform distributions of initial velocities and positions of the swash front at the beginning of a swash cycle reproduces the measurements except for parts of one experiment where limited surveys and a significant low frequency component to swash motions might have caused errors in model initialization

directional spreading of waves in the nearshore observations of surface gravity waves shoaling between 8 m water depth and the shoreline on a barred beach indicate that breaking results in an increase in the directional spread of wave energy in contrast to the directional narrowing with decreasing depth predicted by refraction theory snell s law during low energy wave conditions when breaking induced wave energy losses over the instrumented transect are small the observed mean propagation direction and spread about the mean both decrease with decreasing depth consistent with the expected effects of refraction nonlinearity causes high frequency components of the spectrum to become directionally aligned with the dominant incident waves during high energy wave conditions with significant wave breaking on the sand bar the observed mean directions still decrease with decreasing depth however the observed directional spreads increase sharply nominally a factor of 2 for values integrated over the swell sea frequency range between the outer edge of the surf zone and the crest of the sand bar followed by a decrease toward the shoreline observations on a nonbarred beach also show directional broadening with spreads increasing monotonically from the outer edge of the surf zone to a maximum value near the shoreline although the mechanism is not understood these spatial patterns of directional broadening suggest that wave breaking causes significant scattering of incident wave energy into obliquely propagating components

structural analysis and vein episode of the penjom gold deposit malaysia implications for gold mineralisation and tectonic history in the central belt of malaysia abstract gold mineralisation at the penjom gold deposit in the central belt of peninsular malaysia is dominantly hosted in structurally controlled quartz carbonate veins that display a variable degree of overprinting events under a ductile brittle regime mineralised veins are categorised into two main episodes fold and thrust related veins mainly comprised of bedding and penjom thrust parallel shear veins and associated extension veins developed during a d2 event in addition ne to nne trending splays and penjom thrust parallel reverse dextral and locally nnw to ns reverse sinistral faults overprint earlier vein events forming a new episode of extensional veins during d3 event mostly at the fault contacts of intrusives either as shallow dipping or vertical sheeted stockwork or brecciated veins at least two episodes of faulting d4 d5 are evident which postdates the main episodes of veining and mineralisation this is indicated by a series of late episodes ns trending sinistral and oblique to normal faults which transect and displace the penjom thrust and the folded footwall sequence at low angles and responsible for intensive vein deformation along the penjom thrust and displacement of ore body structural interpretations of mineralised veins suggest that the veins were formed under a compressional to transpressional regime with later post vein displacement in a transtensional to extensional regime vein formation in response to deformation observed at penjom reflects regional structural deformation within the central belt of peninsular malaysia and specifically along the bentong raub suture zone

evidence from mossbauer spectroscopy for intense localization of metamorphic fluid flow during the formation of spaced cleavage arenites in the low grade metasedimentary rocks of the stirling barren group western australia contain discrete spaced cleavages these in part are pure white mica but up to 30 of the cleavage zones consists of fine grained quartz resulting from crystal plastic deformation a modified gresens analysis shows that the cleavage domains formed by a 50 volume loss associated primarily with sio2 and mgo concentration decreases of 58 and 37 respectively and a 12 decrease in fe2o3 mossbauer spectroscopy shows that the fe2 fe3 ratio from lithon to cleavage changed from 50 so to 15 85 this substantial difference cannot be accounted for by loss of iron the data are best explained by the focusing of a highly oxidizing fluid through the cleavage domains where volumetric fluid rock ratios around 150 to 1 are indicated in this example advectic processes appear to be important in low grade regional metamorphism

low frequency swash motion induced by wave grouping abstract this paper concerns the low frequency motion of swash directly induced by wave grouping on a steep beach a new experimental investigation is presented which considers the hydrodynamics of the inner surf zone and swash zone using vertical wave gauges and a run up wire results for regular waves wave groups and random waves are discussed with particular reference to low frequency motions the inner surf zone and swash zone are found to be unsaturated at incident short wave frequencies and as a result significant wave grouping is apparent at the shoreline the low frequency motion in the surf zone is found to be in phase with the incident wave grouping and may therefore be regarded as a time varying set up watson and peregrine 1992 the low frequency motion of the swash is shown to be an order of magnitude greater than that in the inner surf zone inconsistent with cross shore standing long waves for which no evidence is found we demonstrate that the low frequency motion of the shoreline provides an excellent approximation to the run up of individual bores and therefore describes the run up envelope spectral analysis shows that the low frequency motion of the swash is directly linked to the modulations in offshore wave height i e the low frequency energy in the incident wave envelope in addition the random wave run up spectra show an f 4 high frequency roll off as found by huntley et al 1977 the accumulated data show that unless the surf zone is totally saturated a significant proportion of the low frequency swash motion may be directly due to incident wave grouping and not standing long waves

laminated veins and hydrothermal breccia as markers of low angle faulting rhenish massif germany abstract the emplacement of bedding veins and vein breccia in a fold and thrust belt setting is discussed we relate vein types to thrusting regimes using the rhenish massif in germany as case example the rhenish massif is a slate belt in a hercynian fold and thrust system the slate belt cleavage generally dips to the southeast and locally has been rotated into low angle shear zones parts of these are parallel to bedding and marked by quartz carbonate veins both shear veins and extensional veins are distinguished on the basis of fibrous crack seal microstructures most shear veins grew by incremental pull apart between en echelon slip surfaces s0 the overlap of which produced a vein stack the stacks have a lineation l0 resulting from a combination of slip fibre growth and dissolution pressure solution slip the attitude of l0 relative to fold axes and the asymmetry of vein microstructures are consistent with vein emplacement during the hercynian thrusting early shear zone veins were thrusted mylonitized and finally boudinaged or folded depending on their setting the shear veins include coeval sheets of vein hosted breccia the breccia contains angular fragments of mylonitized veins and slate the orientation of s0 and s1 in the breccia varies randomly per fragment indicating random fragment rotation unencumbered spin of country rock debris implies rock expansion possibly by rapid pull apart events during the thrusting

a data variance technique for automated despiking of magnetotelluric data with a remote reference abstract the magnetotelluric method employs co located surface measurements of electric and magnetic fields to infer the local electrical structure of the earth the frequency dependent apparent resistivity curves can be inaccurate at long periods if input data are contaminated even when robust remote reference techniques are employed data despiking prior to processing can result in significantly more reliable estimates of long period apparent resistivities this paper outlines a two step method of automatic identification and replacement for spike like contamination of magnetotelluric data based on the simultaneity of natural electric and magnetic field variations at distant sites this simultaneity is exploited both to identify windows in time when the array data are compromised as well as to generate synthetic data that replace observed transient noise spikes in the first step windows in data time series that contain spikes are identified according to an intersite comparison of channel activity such as the variance of differenced data within each window in the second step plausible data for replacement of flagged windows are calculated by wiener filtering coincident data in clean channels the wiener filters which express the time domain relationship between various array channels are computed using an uncontaminated segment of array training data examples are shown where the algorithm is applied to artificially contaminated data and to real field data in both cases all spikes are successfully identified in the case of implanted artificial noise the synthetic replacement time series are very similar to the original recording in all cases apparent resistivity and phase curves obtained by processing the despiked data are much improved over curves obtained from raw data

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

multiple origin and regional significance of bedding parallel veins in a fold and thrust belt the example of a carbonate slice along the appalachian structural front abstract the development and evolution of bedding parallel veins bpv are investigated in the saint dominique carbonate slice southern quebec appalachian structural front in order to emphasize the regional significance of bpv in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution structural and microstructural analyses reveal that most bpv display a laminated structure locally crosscut by a massive one both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets indicating that bpv cementation and deformation are continuous processes opening both sub parallel and sub perpendicular to the bpv walls are documented early bpv are planes of weakness that focus later reactivation and evidence of successive and sometimes opposite senses of opening are locally preserved within a single bpv the bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise petrographic and geochemical 18 o vpdb and 13 c analyses of structural cements suggest a common locally derived source for the fluids that percolated through bpv non bedding parallel veins and faults the isotopic ratios also reveal a significant enrichment in 18 o and 13 c through time this evolution is tentatively correlated with tectonic syn convergence exhumation of the saint dominique slice during its imbrication along the appalachian structural front after its burial under taconian thrust sheets

low frequency magnetic field measurements near the epicenter of the ms 7 1 loma prieta earthquake the authors report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the m sub s 7 1 loma prieta earthquake of 17 october 1989 their measurements cover 25 narrow frequency bands in the more than six decade frequency range 0 01 hz 32 khz with a time resolution varying from a half hour in the ulf range 0 01 10 hz to one second in the elf vlf range 10 hz 32 khz the ulf system is located near corralitos about 7 km from the epicenter the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf system is located on the stanford campus about 52 km from the epicenter analysis of the elf vlf data has revealed no precursor activity that they can identify at this time however the ulf data have some distinctive and anomalous features first a narrow band signal appeared in the range 0 05 0 2 hz around september 12 and persisted until the appearance of the second anomalous feature which consisted of a substantial increase in the noise background starting on 5 october and covering almost the entire frequency range of the ulf system third there was an anomalousmore dip in the noise background in the range 0 2 5 hz starting one day ahead of the earthquake finally and perhaps most compelling there was an increase to an exceptionally high level of activity in the range 0 01 0 5 hz starting approximately three hours before the earthquake there do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase further while the systems are sensitive to motion seismic measurements indicate that there were no significant shocks preceding the quake thus the various anomalous features in the data and in particular the large amplitude increase in activity starting three hours before the quake may have been magnetic precursors less

results of ulf magnetic field measurements near the epicenters of the spitak ms 6 9 and loma prieta ms 7 1 earthquakes comparative analysis the characteristics of the ulf magnetic field emissions measured at two magnetic observatories in the republic of georgia prior to and after the ms 6 9 earthquake that occurred near spitak armenia on december 7 1988 are compared with the apparently similar emissions associated with the ms 7 1 earthquake that occurred near loma prieta california on october 17 1989 the main features of the spitak measurements according to observations made at the dusheti station 128 km to the spitak epicenter as compared with the loma prieta measurements which were made at corralitos california 7 km to the loma prieta epicenter are the following 1 the intensity of ulf background activity started growing 3 to 5 days before the spitak earthquake whereas the corresponding increase in activity began 12 days before the loma prieta earthquake 2 a substantial ulf emission burst was recorded at dusheti starting 4 hours prior to the main shock a similar large burst of ulf activity commenced 3 hours before the loma prieta event and continued until the occurrence of the main shock 3 ulf activity remained high for about two weeks after the spitak earthquake and for several months after the loma prieta earthquake 4 ulf noise bursts were observed 1 to 6 hours before powerful aftershocks at spitak during the period of enhanced activity but there was no conclusive link between the ulf noise at corralitos and the after shocks a major difference in the ulf activity preceding the two earthquakes is a difference in amplitude 0 2 nt at spitak and 5 nt at loma prieta but this is easily explained as being caused by the different distances of the observation stations from the epicenters

a model for sorted circles as self organized patterns sorted circles emerge as self organized patterns from a laterally uniform active layer that becomes laterally sorted as frost heave deforms the interface between a stone layer and an underlying soil layer in a three dimensional cellular model of the active layer cyclic freezing and thawing drives transport of stone and soil particles by 1 addition of ice particles representing soil expansion by frost heave 2 removal of ice particles representing soil consolidation during thawing 3 addition of void particles a discrete abstraction of soil compressibility representing soil expansion by water absorption 4 removal of void particles representing compaction and desiccation of underlying soil by frost heave 5 relaxation of surface morphology by soil creep and stone avalanche and 6 vertical sorting of stones and soil by illuviation these transport processes give rise to sorted circles which are characterized by a mean spacing of 3 6 m a 2 4 m wide soil domain surrounded by a 1 0 m wide 0 3 m high annulus of stones and a 750 year period of circulation in the soil domain all consistent with measured characteristics of sorted circles in western spitsbergen in the model instabilities on the stonesoil interface grow upward as soil plugs by drawing in soil from the surrounding subsurface soil layer soil plugs develop into sorted circles as they contact the ground surface simultaneously elevating an encircling annulus of stones sorted circles are dynamically maintained by circulation within the stone and soil domains initiation of soil plugs is driven by a positive feedback in which frost heave near the stone soil interface pushes soil toward more compressible soil regions where the soil layer is thicker the lateral component of these frost heave induced displacements is not reversed during thaw because soil consolidation as ice rich soil melts and drains and soil expansion as desiccated and compacted soil hydrates displace soil vertically further development of soil plugs and sorted circles is determined by an interplay between this positive feedback and amplitude dependent negative feedbacks that result from decoupling of the freezing front from the stone soil interface parameters outside the range in which sorted circles form can result for example in stone islands and labyrinthine patterns the initial wavelength of perturbations on the stone soil interface is accurately predicted using a linear stability analysis but increase in this wavelength through time reflects the nonlinearities that control the spacing of soil plugs and sorted circles namely interactions and mergers between neighboring forms

beach cusps as self organized patterns computer simulations of flow and sediment transport in the swash zone on a beach demonstrate that a model that couples local flow acceleration and alongshore surface gradient is sufficient to produce uniformly spaced beach cusps the characteristics of the simulated cusps and the conditions under which they form are in reasonable agreement with observations of natural cusps the self organization mechanism in the model is incompatible with an accepted model in which standing alongshore waves drive the regular pattern of erosion and deposition that gives rise to beach cusps because the models make similar predictions it is concluded that currently available observational data are insufficient for discrimination between them

investigation of a self organization model for beach cusp formation and development a recent numerical investigation of self organization werner and fink 1993 suggests that the feedback process between currents and sediment response can result in self organized patterns and can be used to predict beach cusp formation and spacing a similar model based on self organization is tested here in order to understand the processes occurring during beach cusp formation and development to evaluate the sensitivity toward the parameters used and to examine how the model might relate to field observations results obtained confirm the validity of the self organization approach and its capacity to predict beach cusp spacing with values in fair agreement with the available field measurements with most of the input parameters primarily affecting the rate of the process rather than the final spacing however changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior cusp spacing tends to change with time and cusp regularity shows large long term variations cusps are found to be accretionary in the swash zone and in agreement with most observations mean flows are horn divergent over developed topography simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed results indicate that preexisting large amplitude cusps are destroyed if their spacing is substantially different from that expected under self organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach these findings support the hypothesis that self organization is a robust mechanism for beach cusp formation

long term monitoring of ulf electromagnetic fields at parkfield california 1 electric and magnetic fields in the 10 4 1 0 hz band were monitored at two sites adjacent to the san andreas fault near parkfield and hollister california from 1995 to 2007 a data window 2002 2005 enclosing the 28 september 2004 m6 parkfield earthquake was analyzed to determine if anomalous electric or magnetic fields or changes in ground conductivity occurred before the earthquake the data were edited removing intervals of instrument malfunction leaving 875 days in the 4 year period frequent spikelike disturbances were common but were not more frequent around the time of the earthquake these were removed before subsequent processing signal to noise amplitude spectra estimated via magnetotelluric processing showed the behavior of the ultralow frequency fields to be remarkably constant over the period of analysis these first order plots make clear that most of the recorded energy is coherent over the spatial extent of the array three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields transfer function estimates between components at each site were employed to subtract the dominant field and look deeper at the residual fields the data were decomposed into principal components to identify the dominant coherent array modes and the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only and furthermore to distinguish anomalies present in both the electric and magnetic fields from those present in only one field type standard remote reference apparent resistivity estimates were generated daily at parkfield a significant seasonal component of variability was observed suggesting local distortion due to variations in near surface resistance in all cases high levels of sensitivity to subtle electromagnetic effects were demonstrated but no effects were found that can be reasonably characterized as precursors to the parkfield earthquake

characteristics and occurrence of bedding parallel slip surfaces and laminated veins in chevron folds from the bendigo castlemaine goldfields implications for flexural slip folding the occurrence of bedding slip planes and associated slip striated laminated quartz veins in the bendigo castlemaine goldfields southeastern australia was investigated bedding slip planes are concentrated in thin siltstone layers data from surface stratigraphic sections on the limbs of five major anticlines gave a mean slip plane spacing of 8 9 m n 96 and a mean laminated vein thickness of 19 mm most laminated veins are 20 mm thick and discontinuous along strike and around fold hinges thicker veins are correspondingly more continuous and are traceable around fold hinges the mean thickness of laminated veins from individual fold limbs increases with increasing mean spacing of slip planes on each limb suggesting a sympathetic relationship between vein thickness and net slip however there is no such correlation between individual vein thickness and spacing these relations are explained using a model for the progressive generation of bedding slip planes via shear failure at competent incompetent layer interfaces as a result of shear strain rate incompatibilities between competent and incompetent beds during fold limb steepening the model predicts flexural slip activity continuing well into the stage of homogeneous flattening of the folds and gives rise to a population of slip planes dominated by those with low net slip

flexural slip generated bedding parallel veins from central victoria australia abstract thin continuous laminated bedding parallel quartz veins bpvs with slip striated and fibred vein walls occur within slates or at their contact with sandstones on the limbs of chevron folds in the bendigo castlemaine goldfields southeastern australia two microstructural types of bpv i and ii have been previously recognized and are confirmed in this study both types are concluded to have formed during and or after crenulation cleavage the first tectonic axial planar structure in the wallrock slates and during flexural slip folding type i bpvs consist of syntaxial phyllosilicate inclusion trails parallel to bedding enclosing inclined inclusion bands the latter formed by detachment of wallrock phyllosilicate particles from the walls of pressure solution segmented discordant tension veins type i bpvs are formed by bedding parallel shear and grow in width by propagation of the discordant veins into the bpv walls type ii veins are composed of quartz bands separated by wallrock slate seams which have split away from the vein wall during dilatant shear opening they incorporate numerous torn apart fragments of crenulated wallrock slate type i bpv inclusion band average spacing of 0 5 mm probably represents the magnitude of slip increments during stick slip flexural slip folding activity

an oxygen isotope study of two contrasting orogenic vein gold systems in the meguma terrane nova scotia canada with implications for fluid sources and genetic models sampling of quartz vein material from two gold deposits of similar geological setting but different ages the ovens 408 ma dufferin 380 ma in the meguma terrane of nova scotia has been done to compare and contrast their 18oquartz signatures despite different ages of formation quartz from all vein types in each of the deposits i e saddle reef bedding concordant leg reefs en echelon discordant shows limited intra deposit variation with similar average 18o values of 15 2 0 9 n 16 for the ovens and 15 7 0 6 n 12 for dufferin using an average 18o value of 15 4 for the two deposits the corresponding 18oh2o values calculated for 400 c and 350 c based on constraints from mineral assemblages and fluid inclusion studies indicate averages of 11 4 0 2 and 10 2 0 2 respectively the isotopic data indicate that 1 the vein forming fluids have a metamorphic signature 2 all vein types in the two deposits represent formation from a single isotopically homogeneous fluid and 3 a fluid of similar isotopic signature was generated by two contrasting tectono thermal events in the meguma terrane that were separated by 30 ma integration of these results with previously published data for 14 meguma gold deposits indicate a general stratigaphic dependence in 18oh2o values for deposits when arranged in their relative stratigraphic position such that 18oh2o values increase upwards in the stratigraphy this apparent trend cannot be explained by models involving either fluid mixing or cooling of the vein forming fluids but instead is modelled using fluid rock interaction taking into account a change in the modal mineralogy of the metasedimentary rocks upwards in the stratigraphy

kinematics of crystal growth in syntectonic fibrous veins abstract detailed observations of a set of fibrous antitaxial calcite veins in a slate reveal that some of the calcite fibres do not connect material markers on both sides of the vein and can therefore not have tracked the full opening trajectory during vein growth this calls for a better understanding of the mechanisms of fibre formation and reliable criteria to test the tracking hypothesis based on surface roughness characteristics of the vein wall we develop a simple model for shape growth of crystals in a crack seal environment which can account for both tracking and non tracking behaviours and propose a set of tracking criteria for antitaxial veins finally we discuss ways by which the model can be tested against natural examples

mechanics of formation of gold bearing quartz veins nova scotia canada abstract the meguma terrane of nova scotia canada is composed largely of low grade clastic metasediments swarms of structurally complex bedding concordant quartz veins are found across the whole terrane partly or wholly outlining anticlinal domes these veins exhibit spectacular features due to intermittent hydraulic fracturing and healing crack seal such as phyllosilicate inclusion bands columnar quartz grains and included sheets of host rock overprinting all the precipitation features are a suite of deformation structures which include pinch and swell tectonic stylolites and cross cutting extension and hybrid fractures the veins were formed syntectonically in folded and foliated strata the vein precipitating fluids pooling beneath less permeable beds in anticlinal domes fluid migration paths were controlled by the two fundamental mechanical anisotropies in the host rocks bedding and foliation a simple two dimensional vein model is considered using fracture propagation and quartz precipitation rates estimates of rates of vein formation are determined for example it seems possible that a quartz vein 100 m long and 175 cm wide could form in less than 10 yrs such times are effectively geologically instantaneous and have considerable implications with respect to physical and chemical processes in deformation and metamorphism

flexural slip folding in the meguma group nova scotia canada abstract flexural slip folding has been established for two anticlines in the meguma group nova scotia flexural slip postdates the main acadian episode of flexural flow fold growth and represents a late brittle ductile reactivation of the fold belt flexural slip structures are dominated by bedding parallel movement horizons but include a linked system of frontal and lateral ramps and conjugate movement horizons slip amount calculated from displacement of discordant quartz veins combined with vein spacing indicates an average local shear strain of approximately 0 5 however because flexural slip occurred when the fold limbs were steep the shear strain accounts for a small change in limb dip 4 8 variation of slip amount with spacing of movement horizons suggests progressive flexural slip was accommodated by continuous initiation of new movement horizons as well as continuing slip on existing movement horizons the presence of quartz veins along flexural slip structures together with evidence for ductile deformation coeval with flexural slip suggests that slip episodes were fluid assisted and intermittent separated by periods of ductile deformation and build up of fluid pressure flexural slip veins in the ovens anticline are auriferous and a flexural slip model may be appropriate for other similar meguma gold deposits thrust sheets up to 10 m thick occurring on a fold limb are interpreted to have originated in flat box fold hinges and to have been placed onto the steep limbs of the chevron folds during the flexural slip episode thrusting may have assisted the transformation of a box fold into a chevron

geoelectric potential changes possible precursors to earthquakes in japan whether electromagnetic precursors to earthquakes eqs exist is an important question not only for eq prediction but also for understanding the physical processes of eq generation slow transient geoelectric potential changes have been observed before several recent eqs in japan in most cases they appeared 1 19 days before the eqs and their duration and intensity were several minutes to 1 h and 1 2 mv 100 m the changes appeared before five of all six eqs with magnitude 5 that occurred within 20 km of our stations during the observation period changes were also detected at greater epicentral distances up to 75 km before two other eqs including one eq of magnitude 4 7 which was preceded by a signal simultaneously recorded at three widely separated stations these geoelectric potential changes have been distinguished through the following criteria from a multitude of other changes which were noise of various origins i the selected changes were proportional in amplitude to the length of the recording station s short 100 m dipoles and were simultaneously detected also on long 1 10 km dipoles when the latter were in operation ii no such changes occurred during the observation period that were not followed by eqs although the eq precursory nature of these geoelectric potential changes is admittedly unproven it seems that the present results warrant continued serious research into the occurrence generation and transmission of these signals and their possible causal relationship to eqs

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

late structural control of mesothermal vein hosted gold deposits in central victoria australia mineralization mechanisms and exploration potential abstract comparison of the structural relationships between five gold deposits in ordovician rocks of the central victorian slate belt reveals a similar history and structural control of gold mineralization large quartz veins spatially associated with gold mineralization such as the famous saddle reefs of bendigo formed during the second deformation earlier than the gold mineralization itself where they were overprinted by the effects of the fourth deformation they provided structural sites for gold deposition on their boundaries with country rock where brecciation jostling and fracture were favoured access of fluids resulting from metamorphism and deformation to the brecciated fractured and jostled blocks of country rock created conditions suitable for the precipitation of gold through a sequence of alteration replacement and infill the dominant structural relationships that resulted in the generation of these sites were a the high angle of the axial plane of the fourth deformation to earlier structures and b the presence during mineralization of large pre existing quartz veins that acted as structural discontinuities on which brecciation could occur these factors allow a predictive capacity for exploration in the region

seismomagnetic effects from the long awaited 28 september 2004 m 6 0 parkfield earthquake precise measurements of local magnetic fields have been obtained with a differentially connected array of seven synchronized proton magnetometers located along 60 km of the locked to creeping transition region of the san andreas fault at parkfield california since 1976 the m 6 0 parkfield earthquake on 28 september 2004 occurred within this array and generated coseismic magnetic field changes of between 0 2 and 0 5 nt at five sites in the network no preseismic magnetic field changes exceeding background noise levels are apparent in the magnetic data during the month week and days before the earthquake or expected in light of the absence of measurable precursive deformation seismicity or pore pressure changes obser vations of electric and magnetic fields from 0 01 to 20 hz are also made at one site near the end of the earthquake rupture and corrected for common mode signals from the ionosphere magnetosphere using a second site some 115 km to the northwest along the fault these magnetic data show no indications of unusual noise before the earthquake in the ulf band 0 01 20 hz as suggested may have preceded the 1989 ml 7 1 loma prieta earthquake nor do we see electric field changes similar to those suggested to occur before earthquakes of this magnitude from data in greece uni form and variable slip piezomagnetic models of the earthquake derived from strain displacement and seismic data generate magnetic field perturbations that are con sistent with those observed by the magnetometer array a higher rate of longer term magnetic field change consistent with increased loading in the region is apparent since 1993 this accompanied an increased rate of secular shear strain observed on a two color edm network and a small network of borehole tensor strainmeters and increased seismicity dominated by three m 4 5 5 earthquakes roughly a year apart in 1992 1993 and 1994 models incorporating all of these data indicate increased slip at depth in the region and this may have played a role in the final occurrence of the 28 september 2004 m 6 0 parkfield earthquake the absence of electric and magnetic field precursors for this and other earthquakes with m 5 7 3 elsewhere in the san andreas fault system indicates useful prediction of damaging earthquakes seems unlikely using these electromagnetic data

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

compositional variation of phlogopite in a marble sample implications for geological thermobarometry the textural and compositional features of phlogopites in a contact metamorphic dolomite marble inclusion in the bergell intrusion central alps and in a metasomatic reaction vein cutting through this marble suggest different origins for vein phlogopites a high al vein phlogopite represents former marble phlogopite which has been compositionally modified by reaction with the vein forming fluid b low al vein phlogopite represents phlogopite precipitated from the vein forming fluid as both types of vein phlogopite were in contact with the same vein forming fluid at the same time low al phlogopite most likely represents an equilibrium phlogopite composition whereas high al phlogopite does not high al vein phlogopite retained its al content from the contact metamorphic marble parent phlogopite and only underwent fe mg exchange with the metasomatic fluid all the vein phlogopites studied are strongly enriched in fe relative to marble phlogopite the data may suggest in general that phlogopite al si ratios may be retained from the conditions under which the phlogopites first formed whereas the mg fe ratios may be substantially modified by exchange with other ferromagnesian solid phases and or a metamorphic fluid at later stages in their metamorphic history this may have significant effects on calculated pressures and temperatures from thermobarometers involving biotite

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

crack seal fibre growth mechanisms and their significance in the development of oriented layer silicate microstructures abstract an analysis of crack seal fibre growth mechanisms has shown two important implications of the crack seal process for the interpretation of microstructures in low grade metamorphic rocks 1 1 the ability of fibre growth to track the incremental separation history of crack walls depends on details of the nucleation and growth mechanisms 2 2 fibrous crystals may develop cristallographic preferred orientations in certain crack seal situations the microstructures of layer silicates and associated phases developed in several examples of syntectonic intragranular microfracture sites and veins indicates that layer silicate 001 and grain shape preferred orientation can develop during crack seal deformation by oriented growth mechanisms during successive crack seal increments preferred orientation may develop in response to an interaction between anisotropic growth kinetics and the displacement history resulting in preferential rejoining by syntaxial overgrowth of pulled apart grains having fast growth directions parallel to the incremental displacement direction across a microcrack preferred orientation may also be developed and enhanced in crack seal growth sites by overgrowth of previously oriented layer silicates in the microcrack walls in this case the crystallographic preferred orientation need not be simply related to the displacement history during crack seal fibre growth since crack seal processes may operate on all scales down to the minimum size of a microfracture in a deforming rock such mechanisms of layer silicate preferred orientation development are expected to be very significant in developing and enhancing foliation during deformation involving microfracture and solution transfer processes

rhenium osmium geochronology of arsenopyrite in meguma group gold deposits meguma terrane nova scotia canada evidence for multiple gold mineralizing events rhenium osmium geochronology using arsenopyrite was undertaken for three gold deposits in the meguma terrane nova scotia canada in order to better constrain their age of formation and to assess the utility of arsenopyrite for dating similar deposits globally analyses of arsenopyrite from bedding concordant veins from the ovens locality southwest meguma terrane yield a precise re os isochron age of 409 5 ma arsenopyrite analyses from a bedding discordant vein at this locality indicate an identical re os age of 407 4 ma saddle reef veins from the dufferin deposit northeast meguma terrane contain arsenopyrite with a precise re os isochron age of 380 3 ma the lack of common os in some arsenopyrite samples from both the ovens and dufferin permit calculation of single mineral model ages for each deposit which are identical to those determined using the isochron method initial os compositions for the two vein types at the ovens suggest a predominately crustal source of os in the mineralizing fluids whereas a less radiogenic initial os composition for arsenopyrite from dufferin does not as clearly define a crustal metal source at a third locality the touquoy deposit the re os systematics of arsenopyrite associated with disseminated gold mineralization do not define a precise formation age possibly as a result of mixing of re and os derived from the mineralizing fluid and the shale host rock the re os ages of arsenopyrite indicate that there were at least two distinct periods of gold deposition in the meguma terrane coinciding with widespread tectonothermal events regional deformation and metamorphism associated with acadian orogenesis and widespread generation of meta and peraluminous granites and high grade metamorphism within the basement rocks under the meguma terrane the ca 407 ma age for the ovens arsenopyrite provides the best estimate for the timing of regional acadian deformation in the meguma terrane and is slightly older than previous estimates based solely on 40ar 39ar dating

40ar 39ar dating of hydrothermal biotite from high grade gold ore tangier gold deposit nova scotia further evidence for 370 ma gold metallogeny in the meguma terrane a hydrothermal biotite carbonate alteration zone adjacent to a high grade multi ounce gold vein in the tangier gold deposit meguma terrane nova scotia has given an 40 ar 39 ar plateau age of 374 ma the alteration halo is part of a vein package in the hinge zone of the tangier anticline which contains abundant auriferous quartz veins formed during flexural slip folding during a late stage reactivation of the regional fold belt the 374 ma age is similar to 40 ar 39 ar ages determined for hydrothermal vein minerals at seven other meguma gold districts thereby suggesting a terrane wide metallogenic event a similar age of vein formation and by inference gold mineralization and granite emplacement across the meguma terrane suggest that the cospatial and cotemporal nature of the two geological events may be related an integrated model including anatexis and devolitization of the lower crust possibly as a consequence of overriding a mantle plume in concert with late stage reactivation of the fold belt owing to continued transpression along a terrane bounding fault is proposed

dc trains and pc3s source effects in mid latitude geomagnetic transfer functions magnetotelluric mt data from two sites 150 and 300 km southeast of san francisco california geomagnetic dipole latitude 43 degrees l approximately 1 9 show that the usual mt assumption of spatially uniform external magnetic fields is violated to a significant degree in the period range 10 30 s inter station transfer functions exhibit large systematic temporal variations which are consistent with a combination of two distinct sources electromagnetic noise due to the san francisco bay area rapid transit bart dc electric railway and pc3 geomagnetic pulsations there is a suggestion in the data that some of the pc activity may actually be excited by bart