scale dependence of seismic energy to moment ratio for strike slip earthquakes in japan we analyzed four pairs of a large m w 6 and a small m w 3 5 to 4 shallow strike slip earthquakes to investigate the scale dependence of the seismic energy to moment ratio an important macroscopic parameter which reflects the basic physical process of seismic slip these earthquakes occurred in the south western part of japan and high quality close in records epicentral distance 50 km are available for both the small and large earthquakes the paired events have almost the same focal mechanism and hypocenter location we used the spectral ratio of the paired events in order to remove the effects of attenuation along the wave propagation path and the station site response we then estimated the seismic energy from the source spectra estimated from the spectral ratio the energy to moment ratio increases with the earthquake size this scale dependence is very similar to that found earlier for earthquakes in southern california

estimation of radiated energy using the kik net downhole records old method for modern data we use kik net nied down hole records to estimate the radiated energy er of 29 japanese inland earthquakes with a magnitude range from mw 5 6 to 7 0 the method is based on the work of gutenberg and richter in which the time integral of s wave ground motion velocity squared is measured as a basic metric of the radiated energy only stations within a distance of 100 km are used to minimize complex path and attenuation effects unlike the teleseismic method that uses mainly p waves the use of s waves which carry more than 95 per cent of the radiated energy allows us to obtain robust results we calibrate the method using synthetic seismograms to modernize and improve the gutenberg richter method we compute synthetic seismograms for a source model of each event with a given source function i e known er the actual mechanism and the source station geometry then we compare the given er with the computed energy metric to correct for the unknown effect of wave propagation and the mechanism the use of down hole records minimizes the uncertainty resulting from the site response our results suggest that the currently available estimates of er from teleseismic data are probably within a factor of 3 on average of the absolute value the scaled energy er er m0 is nearly constant at about 3 10 5 over a magnitude range from mw 5 6 to 7 0 with a slight increasing trend with mw we found no significant difference in er between dip slip and strike slip events

evidence for non constant energy moment scaling from coda derived source spectra 1 we present two lines of evidence showing the ratio of seismically radiated energy er to seismic moment mo increases with increasing moment for crustal events spanning 5 orders in seismic moment this ratio often referred to as the scaled energy er m0 has been elusive and the subject of recent debate within the seismological community because significant frequency dependent corrections must be made to account for source and path heterogeneity it is not uncommon that energy estimates of the same event by different researchers have significantly different values to minimize some of the potential problems we used the regional coda methodology outlined by mayeda et al 2003 on 4 large earthquake sequences mw 7 4 and 7 2 izmit duzce mw 7 2 gulf of aqaba mw 7 3 landers and mw 7 2 hector mine this methodology has been shown to provide the lowest variance estimate of the source spectrum when compared against traditional direct wave estimates in our first approach we made energy estimates from coda derived spectra and observed that increases with increasing moment for 3 7 mw 7 4 in our second approach we used the simple idea outlined by prieto et al 2004 to directly test for self similarity under self similarity earthquake source spectra scaled by 3 should have the same shape to test this one needs very stable spectra either through spectral stacking of direct wave spectra or by the use of stable coda derived spectra for all sequences we found that the mainshocks and larger aftershocks had significantly different spectral shapes than the smaller events the scaled 3 spectra of the larger events represented an upper bound having larger amplitudes near the corner frequency in fact an 3 5 scaling moved the larger events closer to the mean of the spectral population though the spectral shape differences persisted these results strongly suggest that earthquakes are not scaling self similarly and that complexities in the rupture process such as variable slip velocity exist between small and large events

silurian orogenesis in the western penobscot bay region maine new 40ar 39ar mineral ages from rocks collected west of penobscot bay maine indicate this region was regionally deformed metamorphosed to amphibolite facies conditions and intruded by plutons in silurian times rather than in the devonian as previously assumed disturbed hornblende age spectra along with the presence of some devonian felsic plutons and extensive retrograde metamorphic textures do suggest however that these rocks were subsequently affected by low grade devonian thermal events in sharp contrast rocks west of the sennebec pond thrust fault a major tectono stratigraphic boundary in this region lack a significant silurian tectono thermal signature and instead record the effects of intense devonian deformation and high grade regional metamorphism the data suggest the two regions experienced very different pre devonian histories and were most likely juxtaposed by the sennebec pond thrust fault in latest silurian to early devonian time rocks now exposed east of the sennebec pond faul

a nonlinear method to estimate source parameters amplitude and travel times of teleseismic body waves abstract we present a nonlinear waveform inversion method to determine source parameters under point source approximation depth source time function centroid moment tensor and seismic moment and also travel times and amplitudes of body waves from teleseismic records we demonstrate that our source time function estimates significantly improve correlation between observed and synthetics broadband seismograms the scaling of source dimensions with seismic moment is similar for deep and shallow events in the japanese subduction area for moment magnitudes between 6 1 and 7 5 we compare event depths and moment tensors obtained with our method to those reported by different institutions for a set of japanese earthquakes this comparison reveals that our method gives hypocentral depths closer to those obtained with regional arrays than other teleseismic methods the seismic moment is properly recovered but data weighting strongly influences the moment tensor solution focal mechanisms are biased by high frequency body wave amplitude variations due to crustal structure below the stations and by errors on the instrument responses body wave differential travel times are improved compared with phase picking measurements the high quality travel times will be exploited to obtain more precise event locations and higher resolution tomographic models online material coordinates of japanese earthquakes processed in this study

solving for source parameters using nested array data a case study from the canterbury new zealand earthquake sequence the seismic spectrum can be constructed by assuming a brune spectral model and estimating the parameters of seismic moment m 0 corner frequency f c and high frequency site attenuation using seismic data collected during the 2010 2011 canterbury new zealand earthquake sequence we apply the non linear least squares gauss newton method a deterministic downhill optimization technique to simultaneously determine the m 0 f c and for each event station pair we fit the brune spectral acceleration model to fourier transformed s wave records following application of path and site corrections to the data for each event we solve for a single m 0 and f c while any remaining residual kappa kappa text r is allowed to differ per station record to reflect varying high frequency falloff due to path and site attenuation we use a parametric forward modeling method calculating initial m 0 and f c values from the local gns new zealand catalog m w gns magnitudes and measuring an initial kappa text r using an automated high frequency linear regression method final solutions for m 0 f c and kappa text r are iteratively computed through minimization of the residual function and the brune model stress drop is then calculated from the final best fit f c we perform the spectral fitting routine on nested array seismic data that include the permanent geonet accelerometer network as well as a dense network of nearly 200 quake catcher network qcn mems accelerometers analyzing over 180 aftershocks m w gns 3 5 that occurred from 9 september 2010 to 31 july 2011 qcn stations were hosted by public volunteers and served to fill spatial gaps between existing geonet stations moment magnitudes determined using the spectral fitting procedure m w sf range from 3 5 to 5 7 and agree well with m w gns with a median difference of 0 09 and 0 17 for geonet and qcn records respectively and 0 11 when data from both networks are combined the majority of events are calculated to have stress drops between 1 7 and 13 mpa 20th and 80th percentile correspondingly for the combined networks the overall median stress drop for the combined networks is 3 2 mpa which is similar to median stress drops previously reported for the canterbury sequence we do not observe a correlation between stress drop and depth for this region nor a relationship between stress drop and magnitude over the catalog considered lateral spatial patterns in stress drop such as a cluster of aftershocks near the eastern extent of the greendale fault with higher stress drops and lower stress drops for aftershocks of the 2011 m w gns 6 2 christchurch mainshock are found to be in agreement with previous reports as stress drop is arguably a method dependent calculation and subject to high spatial variability our results using the parametric gauss newton algorithm strengthen conclusions that the canterbury sequence has stress drops that are more similar to those found in intraplate regions with overall higher stress drops that are typically observed in tectonically active areas

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

strain and displacement across the pinaleno mountains shear zone arizona u s a abstract the 27 km long 0 5 km thick mylonite zone of the pinaleno mountains metamorphic core complex is interpreted as a normal displacement simple shear zone on the basis of major minor and microscopic scale structures shear strains calculated as a function of the angle between the foliation and the lower boundary of the shear zone range from 2 to 19 and have a mean value of 3 5 corresponding to a mean angular shear of 74 these values are the same as those calculated independently from rotations of sheared lithologic contacts integration of the calculated shear strains yields a minimum translation estimate of 2 9 km

a new spectral ratio method using narrow band coda envelopes evidence for non self similarity in the hector mine sequence 1 the use of local and regional s wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs we first compared amplitude ratio performance between local and near regional s and coda waves in the san francisco bay region for moderate sized events then applied the coda spectral ratio method to the 1999 hector mine mainshock and its larger aftershocks we find 1 average amplitude ratio standard deviations using coda are 0 05 to 0 12 roughly a factor of 3 smaller than direct s waves for 0 2 f 15 0 hz 2 coda spectral ratios for the mw 7 0 hector mine earthquake and its aftershocks show a clear departure from self similarity consistent with other studies using the same datasets and 3 event pairs green s function and target events can be separated by 25 km for coda amplitudes without any appreciable degradation in sharp contrast to direct waves

the snake range decollement an exhumed mid tertiary ductile brittle transition the snake range decollement srd in east central nevada separates supracrustal rocks extended by normal faulting from ductilely deformed igneous and metamorphic rocks a well known stratigraphy unaffected by earlier faulting permits analysis of both upper and lower plate strain leading to a better understanding of how vastly different rock types and deformational styles are juxtaposed along low angle faults in metamorphic core complexes middle cambrian to permian upper plate rocks are cut by two generations of ne trending east directed normal faults both generations were initiated as high angle 60 planar faults that flattened abruptly into the srd and rotated domino style to low angles yielding a total rotation of bedding of about 80 90 faulting is tertiary in age as 35 m y old volcanic rocks are involved and resulted in about 450 500 extension in a n55w s55e direction the srd developed as a subhorizontal surface 6 7 km deep at the top of the cambrian pioche shale lower plate granitic rocks and their late precambrian cambrian metamorphic country rocks were involved in progressive ductile to brittle extension at low greenschist grade forming a penetrative subhorizontal foliation and n55 70w lineation that increases in intensity eastward and upward toward the srd stretching and thinning in the lower plate is coaxial and comparable in magnitude to upper plate extension and is interpreted as synchronous k ar ages ranging from 20 to 40 m y in the lower plate suggests the n snake range represents a tertiary thermal anomaly we conclude that the srd developed as a ductile brittle transition zone at 6 7 km depth gravity data suggests that the gently domed srd is cut by younger basin and range faults but the geology of adjacent ranges suggests that the srd does not continue more than 60 km in any given direction the lack of stratigraphic omission across the srd rules out large amounts of movement on a surface that originally cut downsection and we suggest that extensional detachment faults such as the srd can be developed locally as boundaries between brittlely extended rocks and underlying ductile extension and intrusion

rapid determination of p wave based energy magnitude insights on source parameter scaling of the 2016 central italy earthquake sequence we propose a p wave based procedure for the rapid estimation of the radiated seismic energy and a novel relationship for obtaining an energy based local magnitude mle measure of the earthquake size we apply the new procedure to the seismic sequence that struck central italy in 2016 scaling relationships involving seismic moment and radiated energy are discussed for the mw 6 0 amatrice mw 5 9 ussita and mw 6 5 norcia earthquakes including 35 ml 4 aftershocks the mw 6 0 amatrice earthquake shows the highest apparent stress and the observed differences among the three main events highlight the dynamic heterogeneity with which large earthquakes can occur in central italy differences between estimates of mle and mw allows identification of events which are characterized by a higher proportion of energy being transferred to seismic waves providing important real time indications of earthquakes shaking potential

a stochastic ground motion model for switzerland abstract we present a stochastic ground motion model for switzerland a model for the far field fourier amplitude spectra of earthquakes is first proposed constrained by ground motions observed from small local and regional earthquakes in addition to macroseismic intensities observed from large damaging events in switzerland we then use this model in a stochastic simulation technique to generate predictions of peak ground acceleration and velocity and 5 damped response pseudo spectral acceleration we facilitate the prediction of ground motions from finite fault sources through the use of the r eff distance metric and show that magnitude and distance scaling behavior of events up to m w 7 5 is broadly consistent with next generation attenuation and japanese models ground motion prediction uncertainty is described in terms of between and within event uncertainties through residual analysis of response spectra finally single station sigma is derived accounting for the prediction uncertainty at a given site without the ergodic assumption consistency of the model is emphasized through its compatibility with other seismic hazard products the model is referenced to a generic rock profile that was developed by utilizing velocity profiles of the sites of seismic stations and is calibrated at higher magnitudes to the swiss regional macroseismic intensity prediction model furthermore the model is based on moment magnitudes from the recently developed earthquake catalogue of switzerland 2009 ecos09 the well defined reference for the model means that it can easily be adapted for a site specific application for instance through the use of proxies such as quarter wavelength velocity and travel time average shear wave velocity in the upper 30 m v s 30

empirical relationships between aftershock zone dimensions and moment magnitudes for plate boundary earthquakes in taiwan in this study we establish the empirical relationships between the spatial dimensions of the aftershock zones and moment magnitudes m w for the taiwan region the length l and width w of the aftershock zone of an earthquake is measured by the major and minor axes respectively of the ellipse of a two dimensional gaussian distribution of one day aftershocks our data is composed of 649 mainshocks depth 70 km m w 4 0 7 6 between 1990 and 2011 the relationships between aftershock zone dimensions and m w were obtained by least squares method with the corresponding uncertainties estimated by bootstrap our study confirms that aftershock zone dimensions are independent of faulting types and the seismic moment is proportional to l 3 the ratio w l increases slightly with m w and is independent of faulting types together with previous study our results suggest that earthquakes of both small m w 4 0 and large m w 7 0 magnitudes have similar focal zone geometrical parameters by using the m w s relation where the aftershock zone area s is estimated from l and w we also provide an independent examination of the variations in the median stress drop we find that the median stress drops of strike slip earthquakes are higher than those of thrust events moreover the median stress drops are independent of the moment magnitudes for normal and strike slip events but decrease for large thrust events these results are consistent with the latest global observations regardless of faulting types the median stress drop decreases for larger 6 m w 7 6 and relatively deep depth 60 70 km earthquakes online material effect of up dip rupture propagation on estimated maximum slip duration details on teleseismic and geodetic stations and figures of far field displacements temporal change in slip and snapshots of the semblance value distribution

chronology of tectonothermal activity in the western avalon zone of the newfoundland appalachians the ackley granite was intruded into variably deformed and metamorphosed rocks within the gander and avalon zones of the newfoundland appalachians biotite and hornblende from the pluton record internally concordant 40ar 39ar age spectra that define total gas dates of 352 356 ma these are similar to a previously reported 355 5 ma rb sr whole rock isochron age and indicate relatively rapid post magmatic cooling a feature consistent with the post kinematic character of the pluton in the western avalon zone recrystallized sericitic metavolcanic rocks from the late precambrian love cove and marys town groups display variably discordant whole rock 40ar 39ar age spectra however the samples yield well defined plateau ages of 353 400 ma 11 samples which are interpreted to closely date the regional metamorphism and associated deformation in the western avalon zone this chronology is similar to that of the easternmost gander zone indicating that deformation and metamorphism in the western avalon zone

shear zone model for the origin of metamorphic core complexes core complex tectonite results from simple shear rotational strain within regional ductile shear zones that have accommodated a tertiary crustal stretching the emplacement of younger and or upper level nontectonite rocks on older and or deeper level tectonites is the ordinary and predictable result of normal slip translation along shear zones that cut upward through the local geologic column progressive deformation produces a structural stratigraphy marked from bottom to top by normal country rock protolith mylonitic gneiss tectonite carapace microbrecciated tectonite microbreccia decollement and upper plate detachment rocks as young as mid miocene the reconstructions suggest that local regional crustal stretching locally exceeded 100

rock and stiff soil site amplification dependency on vs30 and kappa κ0 abstract a ground motion prediction equation gmpe specific to rock and stiff soil sites is derived using seismic motion recorded on high v s 30 sites in japan this gmpe applies to events with 4 5 m w 6 9 and v s 30 ranging from 500 to 1500 m s stiff soil to rock sites the empirical site coefficients obtained and the comparison with the simulated site functions show that seismic motion on rock and stiff soil sites does not depend only on v s 30 but also on the high frequency attenuation site properties 0 the effects of the site specific 0 on site amplification are analyzed using stochastic simulations with the need to take into account both of these parameters for rock site adjustments adding the site specific 0 into the gmpes thus appears to be essential in future work the rock site stochastic ground motion simulations show that the site specific 0 controls the frequency corresponding to the maximum response spectral acceleration f amp 1 this observation is used to link the peak of the response spectral shape to 0 in this specific japanese dataset and then to add the effects of high frequency attenuation into the previous gmpe from the peak ground acceleration and up to periods of 0 2 s the inclusion of 0 allows the observed bias to be corrected for the intraevent residuals and thus reduces sigma however this 0 determination is limited to a minimum number of rock site records with m w 4 5 and to distances of less than 50 km

ages of regional metamorphism and ductile deformation in the central and southern appalachians abstract a summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation the ca 480 435 ma taconic event affected most of the piedmont and blue ridge provinces the ca 380 340 ma acadian event was milder and was centered in the west central piedmont and eastern blue ridge the 330 230 ma alleghanian event exhibits an abrupt ductile deformation front in the eastern piedmont and extends an unknown distance eastward below the atlantic coastal plain

a study on kappa value in taiwan using borehole and surface seismic array since the inception of the borehole seismic array deployed by the central weather bureau cwb in taiwan in recent years a large quantity of strong motion records have been accumulated from frequently occurring earthquakes around taiwan that provide the opportunity to investigate the spectral decay parameter kappa and to understand further the site effects of seismic stations in this study we used 133 earthquakes recorded at 30 borehole seismic arrays each array includes two force balance accelerometers one at the surface and the other inside the borehole based on the regression analysis between value and hypocentral distance for each surface borehole station pairs the resulting derived from surface stations are higher than results from borehole stations the estimated values are found to range from 0 032 to 0 097 s at surface and 0 012 to 0 078 s in borehole in comparison with a study of site corrections for earthquake magnitude determination these higher values associated with negative station corrections can correspond to the effect of soil conditions to evaluate station corrections of borehole seismic array we collected records from the cosite stations of taiwan strong motion instrumentation program tsmip and central weather bureau station network cwbsn and then derived a linear relationship between the values and station corrections finally both resulting station corrections and values reveal high coherence in local site conditions

dynamic growth of garnet in granitic magmas in order to improve understanding of how accessory garnet crystallizes in igneous rocks and evaluate it as a mineral recorder of magma history we analyzed 18 o of garnets from the hallowell and togus plutons in south central maine united states by laser fluorination and in situ by ion microprobe two types of garnet are recognized magmatic and locally derived peritectic traverses of some single crystals show both gradual and abrupt changes of 18 o garnet commonly 1 while other garnet grains are isotopically homogeneous rimward increase of 18 o in many crystals indicates that garnet grew while high 18 o metamorphic wall rocks were assimilated peritectic grains have a complementary record of the transfer of high 18 o melts to the plutons in some rocks 18 o varies among neighboring grains evidence that crystals grew episodically or were juxtaposed from different sources during magma mixing garnet faithfully records changing magmatic 18 o and is a valuable tool to decipher magma petrogenesis

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

scale dependence of apparent stress for earthquakes along the subducting pacific plate in northeastern honshu japan apparent stress which quantifies the ratio of high frequency spectral amplitude to the direct current level of source displacement spectra is known to reflect the source rupture process whether this parameter depends on the seismic moment has not yet been well established because of the difficulties in the reliable estimation of high frequency source spectra to overcome this problem we estimate s wave source spectra by using site amplification factors and attenuation factor graphic 1 which are systematically measured by the coda normalization method analyzing horizontal components of velocity seismograms recorded at 70 borehole seismic stations of hi net national research institute for earth science and disaster prevention in northeastern honshu japan we estimate site factors and graphic 2 in the 0 5 32 hz frequency band by using these factors we evaluate the source spectra of 225 small to moderate earthquakes that occurred in and around the subducting pacific plate site amplification factors we obtained strongly depend on frequency and the frequency dependence clearly changes with the lithology and geologic age of rock obtained graphic 3 values decrease with frequency in proportion to the reciprocal of frequency the apparent stresses estimated from s wave spectra clearly increase from 104 to 107 pa with the seismic moment increasing which cannot be attributed to the limited frequency band and other artificial causes the power of scale dependence is estimated as 0 39 0 44 for the seismic moment range from 1011 to 1017 n m some of the scale dependence of apparent stress is attributed to the scale dependence of brune s stress drop 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

source parameters path attenuation and site effects from strong motion recordings of the wenchuan aftershocks 2008 2013 using a non parametric generalized inversion technique

patterns of mineral occurrence in metamorphic rocks patterns in the occurrence of minerals in metamorphic rocks suggest additional opportunities for investigating chemical and physical processes during metamorphism three such patterns are reviewed first trace minerals in metamorphic rocks commonly occur with regular distributions indicating their participation in prograde reactions that can be mapped as isograds examples include the distribution of allanite and monazite in pelitic rocks and of zircon and baddeleyite in siliceous dolomites recognition of these isograds points to the potential for developing a chronology of specific chemical reactions during metamorphism and for defining the p t conditions of those reactions second the mineralogical products of retrograde metamorphism in many cases occur in distinctive associations that are consistent with partial mineral fluid equilibrium examples include the distribution of retrograde calcite quartz and tremolite in siliceous limestones and of retrograde tremolite dolomite brucite and serpentine in siliceous dolomites from contact aureoles among other things application of partial equilibrium to retrograde metamorphic rocks leads to constraints on the amount and direction of fluid flow in contact aureoles as they cool third pseudomorphs are typically absent from prograde metamorphic rocks but are common in retrograde metamorphic rocks the distribution may be explained by the effect of force of crystallization the pattern of occurrence of pseudomorphs thus suggests novel phenomena during metamorphism that develop from an interplay between chemical and mechanical processes

on the characteristics of earthquake stress release variations in japan abstract the amount of stress released during earthquakes is a fundamental characteristic of the earthquake rupture process as such it represents a key parameter for improving our understanding of earthquake source physics and for reliable ground motion prediction large earthquake populations usually show variations in stress release as large as three orders of magnitude but the underlying mechanisms have remained largely elusive and particularly the dependence of stress release on earthquake size is still a matter of debate here i use a unique dataset from japan encompassing earthquakes of a wide magnitude range and spatial coverage to show that stress release variations of crustal earthquakes are strongly correlated with heat flow variations indicating that they are thermally controlled in contrast subcrustal events depict highest stress release in regions of strong subduction interface coupling and overall less pronounced variability as compared with crustal earthquakes stress release is overall only weakly dependent on earthquake size but at local scales i e within individual earthquake sequences the dependence can be very strong and apparently varies with stress regime accounting for these systematic variations reduces the stress release variability on local scale by a factor of two to three as compared with the full earthquake population a finding that is of key significance in the endeavor to reduce the uncertainties in future ground motion predictions

rb sr whole rock and 40ar 39ar mineral ages of the togus and hallowell quartz monzonite and three mile pond granodiorite plutons south central maine their bearing on post acadian cooling history generally synmetamorphic granitic stocks intrude high grade silurian lowermost devonian metasedimentary rocks near augusta maine rb sr whole rock isochrons 8 points each define mutually overlapping crystallization ages of 394 8 m y togus quartz monzonite 387 11 m y hallowell quartz monzonite and 381 14 m y three mile pond biotite granodiorite thereby providing a narrow chronologic bracket for acadian tectonothermal activity in the area igneous hornblende muscovite and biotite display internally concordant 40ar 39ar age spectra with plateau dates of 350 m y hornblende and 300 265 m y muscovite and biotite with an overall southwestward younging trend the mineral dates are similar to those recorded in adjacent portions of the regional metamorphic terrain and suggest a prolonged postmagmatic cooling which closely followed the diachronous northeast southwest post acadian cooling of the country rocks no evidence for a distinct permian thermal overprint of older isotopic systems has been observed

robust determination of earthquake source parameters and mantle attenuation 1 an improved inversion technique is needed to effectively separate the frequency dependence of the source from the intrinsic attenuation of the medium we developed a cluster event method cem in which clusters of nearby events instead of individual events pair with stations to form the basis for measurements ofq value and corner frequency fc we assume that the raypaths from one cluster to a station share an identical q while each event in the same cluster is allowed for only one fcin the inversion process this approach largely reduces the degrees of freedom to achieve a robust inversion we use an optimization algorithm of simulated annealing to solve the nonlinear inverse problem the cem was applied to events at 70 150 km depths in the japan subduction zone recorded by f net we show that the method proposed here leads to better constraints on both source parameters and attenuation the resultantq s in the mantle wedge increase from lower than 300 beneath the arc and back arc to greater than 600 in the fore arc region thefc s satisfy a self similar scaling relationship with seismic moment ofm0 fc 3 with a best fit stress drop of 21 9 6 9 mpa in madariaga s form this contrasts to the stress drop of 1 4 1 1 mpa for a global data set composed of prior measurements for crustal events the results of this study agree with results from previous studies except with an upward deviation due to higher corner frequencies and stress drops

spectral scaling of the aftershocks of the tocopilla 2007 earthquake in northern chile summary we study the scaling of spectral properties of a set of 68 aftershocks of the 2007 november 14 tocopilla m 7 8 earthquake in northern chile these are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments the seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega square spectral decay radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect using a graphical approach we test the scaling of seismic spectrum and the scale invariance of the apparent stress drop with the earthquake size to test whether the tocopilla aftershocks scale with a single parameter we introduce a non dimensional number that should be constant if earthquakes are self similar for the tocopilla aftershocks cr varies by a factor of 2 more interestingly cr for the aftershocks is close to 2 the value that is expected for events that are approximately modelled by a circular crack thus in spite of obvious differences in waveforms the aftershocks of the tocopilla earthquake are self similar the main shock is different because its records contain large near field waves finally we investigate the scaling of energy release rate gc with the slip we estimated gc from our previous estimates of the source parameters assuming a simple circular crack model we find that gc values scale with the slip and are in good agreement with those found by abercrombie and rice for the northridge aftershocks

the eagle pass detachment southeastern arizona product of mid miocene listric normal faulting in the southern basin and range mid miocene low angle normal faulting is an integral part of the regional tectonic strain of the southern basin and range the distinguishing characteristic is the presence of detachments allochthons of moderately to steeply dipping hanging wall rocks resting in very low angle fault contact on structurally deeper generally older footwall rocks rotation of detachment strata was accomplished by imbricate listric normal faulting and coordinated tear faulting regional structural domains each thousands of kilometres in area contain detachments marked by uniform sense of detachment strata rotation the eagle pass detachment 70 km northeast of tucson arizona reveals informative structural details of parts of the system steeply southwest dipping mid miocene volcanic and sedimentary rocks several thousands of metres in thickness rest in very low angle 10 fault contact on precambrian granitic basement detachment strata were faulted into position by ne directed translation accompanied by rotation of strata to steep sw dips the detachment fault which underlies the 25 km2 detachment has the form of a large northeast trending mullion trough with relief of at least 500 m along the keel of the detachment precambrian quartz monzonite was transformed into a hydrothermally altered selvage of microbreccia the steep 80 northwest margin of the mullion trough served as a tear fault along which quartz monzonite was crushed volcanics were dragged and fanglomerate was locally sheared into flattened pebble conglomerate detachments like that at eagle pass resemble slump blocks on a grand scale they are elements of a regional system of extensional deformation which coincides with the belt of cordilleran metamorphic core complexes mid miocene detachment faulting post dates the formation of exposed mylonitic tectonites of core complex affinity but the direction of translation of the detachments is parallel to penetrative lineation in nearby and or underlying tectonite moreover in southeastern arizona examples the sense of translation of detachments matches the sense of simple shear movements disclosed by tectonite fabrics we speculate that large crustal displacements achieved during extension induced formation of tectonite produced a geometric and or dynamic condition which strongly influenced subsequent detachment faulting consequently with renewed or continued extension in mid miocene time deep upper crustal slumping was triggered and detachment rocks were translated along listric normal faults in the direction and sense of the earlier displacements which had accommodated the formation of tectonite

regional metamorphism of the vassalboro formation south central maine usa a case study of the role of fluid in metamorphic petrogenesis progressively metamorphosed carbonate rocks of the vassalboro formation serve a natural laboratory for the investigation of fluid rock interactions during metamorphism an integrated study of their whole rock chemistry mineralogy mineral chemistry and mineral abundances has led to the following results a prograde mineral reactions involved hydrolysis as well as dehydration and decarbonation the hydrolysis reactions have resulted in an almost quantitative extraction of k and na from high grade metacarbonates b prograde mineral reactions buffered the x co 2 of coexisting metamorphic fluid during almost all of the rocks metamorphic history c the carbonate rocks were infiltrated by large volumes of h 2 o rich fluid while the buffering reactions progressed during the metamorphic event some high grade metacarbonates were infiltrated by at least 3 rock volumes of fluid combined buffering and infiltration appears to be a general metamorphic phenomenon in carbonate bearing rocks to depths of 30 km in the crust d there is an excellent positive correlation between the heat budget of individual metacarbonate rock samples and calculated fluid rock ratios convective heat transfer by metamorphic fluids is therefore likely to be an important item in the heat budget of metamorphic terrains consideration of these results leads to a model of regional metamorphism which involves infiltration of rock by large volumes of acid h 2 o rich fluid large scale acid infiltration metasomatism in this model the infiltrating fluid exerts enormous control over the mineralogical evolution of the carbonate rocks during the metamorphic event it drives mineral reactions it changes whole rock chemistry and it supplies heat

dynamic modelling of induced seismicity by using seismic efficiency constraints and a new scaling law for slip weakening distance in the numerical simulation of induced seismicity much attention is generally paid to the calibration of the frictional resistance of the causative fault to obtain a seismic moment consistent with that of the actual event whereas sufficient investigation is not made in the estimation of the slip weakening distance dc as well as in the calibration of seismically radiated energy the present study addresses this problem by numerically and analytically investigating the relation between dc and seismic source parameters first this study performs the dynamic simulation of an induced seismic event caused by a decrease in the effective normal stress the analysis demonstrated that seismic efficiency can be used to improve the accuracy of estimating the critical slip weakening distance and the coefficient of kinetic friction d whilst considering not only seismic moment but also radiated energy in the calibration this gave insight into the development of the new calibration method for induced seismicity that considers energy related seismic source parameters furthermore a new scaling law of the slip weakening distance was derived from the theoretical expression of seismic efficiency considering seismic moment mo and scaled energy hat e the proposed scaling law can yield the relation between dc and mo which is shown to be similar to that obtained from a previous study but additionally considers the relation between seismically radiated energy and dc the dependency of dc on seismically radiated energy implied from the proposed scaling law has been verified from the dynamic analyses where 0 06 was used to place a constraint on dc for seismic events with different magnitudes the developed numerical simulation methodology of induced seismicity as well as the scaling law considering the energy indices significantly contributes to improving the accuracy of back analysis thus leading to a more accurate estimation of the mechanical properties of faults and or shear zones in seismically active regions of deep underground mines or reservoirs composed of discontinuous hard rock masses

rb sr whole rock and 40 ar 39 ar mineral ages of the hartland stock south central maine a post acadian representative of the new hampshire plutonic series the hartland granodioritic stock is an undeformed post acadian representative of the new hampshire plutonic series that intrudes low grade silurian devonian metasedimentary rocks in south central maine a nine point rb sr whole rock isochron defines an age of 360 8 m y for the pluton initial sup 87 sr sup 86 sr 0 7056 3 biotite and hornblende from the pluton display undisturbed sup 40 ar sup 39 ar age spectra with mutually overlapping dates of 362 5 m y seven samples the undisturbed character of the argon isotopic systems suggests that the sup 40 ar sup 39 ar ages date times of post magmatic cooling through temperatures required for retention of argon comparison of the emplacement age defined for the hartland stock with rb sr whole rock isochron dates reported for crystallization of other new hampshire series plutons suggests continuous devonian intrusive activity in new england preceding during and following the acadian orogeny no geochronologic evidence for separating distinct subseries of intrusion can be provided with presently available data

spatial and frequency dependent properties of site amplification factors in japan derived by the coda normalization method we have estimated broadband f 0 5 8 hz site amplification factors at 1800 sites in japan based on the coda normalization method using 4001 seismograms obtained from 48 events the results show that in the low frequency band f 0 5 1 hz the site amplification factor varies over a wide range from 4 to 24 db with larger site amplification factors 8 db in such major basins as kushiro rumoi sapporo aomori sendai niigata tokyo toyama nagoya osaka oita and kagoshima on the other hand the site amplification factor in the high frequency band f 4 8 hz varies over a relatively narrow range from 0 to 18 db at each station and has no clear correlation with the surface geology of each station we then examined the contribution of the site amplification at each station to the anomalous distribution of the intensity pattern during large earthquakes by correcting the observed ground accelerations at each k net and kik net station with their corresponding estimated site amplification factors the corrected pattern of intensity shows simple concentric isoseismal intensity contours around the hypocenter indicating the applicability of our estimates to strong motion predictions we confirmed that our estimates are superior to those derived from geology such as those based on the regression of the averaged s wave velocity from the surface to a depth of 30 m graphic 1 with a smaller standard deviation of intensity variations based on a standard decay function of intensity versus hypocentral distance 1 embed inline graphic 1 gif

fluid flow and diffusion in the waterville limestone south central maine constraints from strontium oxygen and carbon isotope profiles oxygen carbon and strontium isotopic profiles across the margin of the waterville limestone member are used to investigate advective and diffusive transport during metamorphism of the waterville formation in south central maine usa rb sr isotopic systematics were homogenized on the 10 cm hand specimen scale at ages that are within error of the 366 6 ma rb sr whole rock age of the syn metamorphic hallowell pluton this is consistent with a plutonic heat source for this low pressure andalusite and sillimanite grade acadian metamorphic terrane advective displacements of all three isotope profiles at the garnet grade blue rock quarry indicate fluid flow to the east into the limestone and the oxygen isotope profile implies a time integrated fluid flux of 3 2 1 5 m 3 m 2 2 error this cross layer flux is insufficient to cause the observed reaction progress of the muscovite ankerite quartz to biotite anorthite in plagioclase calcite reaction in the 100 m thick waterville limestone member and much of the fluid flow responsible may have been layer parallel the isotope profiles indicate advective diffusive homogenization over distances of 1 5 m 13 c to 6 m 18 o and such homogenization distances are difficult to reconcile with observations of order of magnitude variations in reaction progression the centimetre scale or less it is possible that infiltration occurred during events short lived compared with diffusion that the reactions started at different temperatures dependent on bulk composition or that diffusion of water from layers with less reactants to layers with more reactants was important in driving the biotite producing reaction however variations of fluid composition inferred from the mineral assemblages are apparently inconsistent with diffusion driving reactions progress and models of precursor assemblages do not indicate significant compositional control of the temperature of the first appearance of biotite in the rocks irrespective of the details of flow and diffusive exchange on the centimetre scale the average reaction progress in the waterville limestone member requires significant layer parallel fluid fluxes

variability in earthquake stress drop and apparent stress 1 we apply empirical green s function coda based analysis to four earthquake sequences in japan that span a magnitude range of 1 8 to 6 9 to measure radiated energy corner frequency and stress drop we find no systematic dependence of apparent stress or stress drop on seismic moment for these sequences and find they both are log normally distributed however we identify several anomalous events both energetic and enervated that show sharply different spectral signatures from the rest of the population these events indicate that much of the variation in apparent stress and stress drop is statistically significant which may have important implications for seismic hazard analysis

stress release and source scaling of the 2010 2011 canterbury new zealand earthquake sequence from spectral inversion of ground motion data the canterbury earthquake sequence beginning with the 2010 m w 7 2 darfield earthquake is one of the most notable and well recorded crustal earthquake sequences in a low strain rate region worldwide and as such provides a unique opportunity to better understand earthquake source physics and ground motion generation in such a tectonic setting ground motions during this sequence ranged up to extreme values of 2 2 g recorded during the february 2011 m w 6 2 event beneath the city of christchurch a better understanding of the seismic source signature of this sequence in particular the stress release and its scaling with earthquake size is crucial for future ground motion prediction and hazard assessment in canterbury but also of high interest for other low to moderate seismicity regions where high quality records of large earthquakes are lacking here we present a source parameter study of more than 200 events of the canterbury sequence covering the magnitude range m w 3 7 2 source spectra were derived using a generalized spectral inversion technique and found to be well characterized by the 2 source model we find that stress drops range between 1 and 20 mpa with a median value of 5 mpa which is a factor of 5 larger than the median stress drop previously estimated with the same method for crustal earthquakes in much more seismically active japan stress drop scaling with earthquake size is nearly self similar and we identify lateral variations throughout canterbury in particular high stress drops at the fault edges of the two major events the m w 7 2 darfield and m w 6 2 christchurch earthquakes

p wave attenuation with implications for earthquake early warning several widely implemented and tested earthquake early warning algorithms employ empirical equations that relate earthquake magnitudes with ground motion peak amplitudes and hypocentral distances this approach is effective to the extent that the offline dataset available for setting the fitting coefficients in those equations is of sufficient quality and quantity however to address the problem of having a limited dataset it is instructive to gain physical understanding of the main factors controlling the p wave attenuation in this study theoretical expressions are derived that relate the root mean square rms of the p wave displacement d rms and velocity v rms to the seismic moment stress drop and hypocentral distance the theoretical attenuation laws are then validated against observed attenuation using earthquake data from southern california and japan good agreement is found between observed and predicted ground motions the similar ground motion attenuation in california and japan suggests that the attenuation laws are similarly applicable for the two regions and implies that they may also be implemented in other regions without having to go through a lengthy calibration phase because d rms is more strongly dependent on the seismic moment than v rms use of the attenuation law for d rms yields better magnitude prediction than that of v rms it is shown that the d rms to v rms ratio is proportional to the characteristic length of the rupture and that the stress drop is a function of the seismic moment and the cube of d rms v rms this result paves the way for a new stress drop determination scheme that is totally independent of previously used approaches finally it is shown that the rms of the ground motions are proportional to their peak values

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

imaging the high frequency energy radiation process of a main shock and its early aftershock sequence the case of the 2008 iwate miyagi nairiku earthquake japan to understand the energy release process that operates at the end of the main shock rupture and start of the aftershock activity we propose an inversion method that uses continuous high frequency seismogram envelopes of the main shock and early aftershocks i e events that occur at short times after the main shock in our approach the aftershock sequence is regarded as a continuous energy release process rather than a discrete time series of events to correct for the contribution of coda wave energy excited by multiple scattering we use the theoretical envelope synthesized on the basis of the radiative transfer theory as a green s function the site amplification factors are corrected considering the conservation of energy flux and using the coda normalization method the inverted temporal energy release rate for the 2008 mw 6 9 iwate miyagi nairiku earthquake japan decays following t 1 1 at the lapse time t of 40 900 s after the main shock origin time this exponent of the decay rate is similar to the p value of the modified omori law the amount of estimated energy release is consistent with that calculated from the magnitude listed in the aftershock catalog although the uncertainty is large the location of large energy release at the lapse times of 40 900 s approximately overlaps to that of the aftershocks which surrounds the large energy release area during the main shock faulting the maxima of the energy release rate normalized by the average decay rate distributes following a power law similar to the gutenberg richter law

stress drops and radiated energies of aftershocks of the 1994 northridge california earthquake we study stress levels and radiated energy to infer the rupture characteristics and scaling relationships of aftershocks and other southern california earthquakes we use empirical green functions to obtain source time functions for 47 of the larger m 4 0 aftershocks of the 1994 northridge california earthquake m6 7 we estimate static and dynamic stress drops from the source time functions and compare them to well calibrated estimates of the radiated energy our measurements of radiated energy are relatively low compared to the static stress drops indicating that the static and dynamic stress drops are of similar magnitude this is confirmed by our direct estimates of the dynamic stress drops combining our results for the northridge aftershocks with data from other southern california earthquakes appears to show an increase in the ratio of radiated energy to moment with increasing moment there is no corresponding increase in the static stress drop this systematic change in earthquake scaling from smaller to larger m3 to m7 earthquakes suggests differences in rupture properties that may be attributed to differences of dynamic friction or stress levels on the faults

crustal controls on the genesis of the 400 ma old caledonian granites abstract the c 400 ma caledonian granitoids of the british isles form a high k calc alkaline suite with low k na compared with european hercynian or australian caledonian granites the granites south of the iapetus suture are largely s types and occur within thick geosynclinal prisms of lower palaeozoic flysch sediments the granitoids north of the iapetus suture are largely i types with high ba and sr and with evidence of a significant component of continental crust the overall isotopic features of the granitoids show similarities with lower palaeozoic sediments this is owing to both representing averages of the available crust plus material derived from the mantle the available data are compatible with only a small amount of lewisian material incorporated in the magmas and most of the crust involved was of late precambrian or lower palaeozoic age the high sr characteristics of the british isles 400 ma granitoids a feature generally coupled with absence of a major eu anomaly is best explained in terms of melting of a feldspar absent source which had not gone through a previous feldspar fractionation cycle this is compatible with the source being chiefly mantle and or lower crust that had not had an upper crustal history the existence of a chemical province within the british isles caledonian precludes the possibility that the granites have been brought into their present positions by large sinistral movements as has recently been suggested the high na nature of the province is not due to more extensive seawater metasomatism in the source

shuswap terrane of british columbia a mesozoic core complex the shuswap terrane of the northwest cordillera owes its distinctive characteristics to deformation and high grade regional metamorphism that occurred primarily during the mesozoic within the terrane the monashee complex the overlying selkirk allochthon and the intervening monashee decollement record strain and metamorphism that occurred in middle to late jurassic time during and subsequent to the accretion of a western allochthonous terrane the selkirk allochthon moved eastward across the monashee complex after emplacement of the western allochthonous terrane but before late mesozoic to early cenozoic telescoping of the rocky mountain belt in this latter event the monashee complex and overlying allochthonous slices were transported eastward relative to the north american craton on a sole fault that developed during listric thrusting of the rocky mountain foreland synmetamorphic to late metamorphic elongation lineations and associated fabrics of the mylonitic rocks of the monashee decollement zone were generated by shear strain during the middle jurassic emplacement of the selkirk allochthon and are not related to any upper crustal extension that occurred in the tertiary uplift normal faulting brittle reactivation of the mylonitic decollement zone widespread resetting of k ar and rb sr mineral dates and arching of the terrane are events that culminated in the eocene

radiated seismic energy from coda measurements and no scaling in apparent stress with seismic moment 1 the seismic coda consists of scattered waves that leave the earthquake source in a variety of directions the averaging of source radiation that results leads to stable ground motion spectra that we use as the basis for a robust measurement of radiated wave energy we apply an empirical green s function egf method to the seismic coda in order to investigate scaling of the radiated seismic energy we correct for path effects in the spectra of earthquakes by using a stack of closely located small earthquakes as an egf we apply this approach to four earthquake sequences in western north america that span a magnitude range from mw 3 0 mw 7 1 our estimates of scaled energy are consistent with independent measurements where available we find no dependence in individual seismic energy estimates on source station distance which validates the egf approximation we find that a constant scaled energy of 3 5 10 5 provides a reasonable fit to the data with no dependence of the scaled energy on seismic moment

spectral analysis of k net and kik net data in japan part ii on attenuation characteristics source spectra and site response of borehole and surface stations abstract in this study we apply a nonparametric spectral inversion scheme to a data set of accelerograms recorded by the k net and kik net networks in japan in order to derive attenuation characteristics source spectra and site response for this purpose we use a total of more than 67 000 s wave records from 2178 earthquakes m jma 2 7 8 obtained at 1555 stations at the earth s surface and more than 29 000 records from 1826 events recorded at 637 borehole stations at depths of 100 to 3000 m attenuation characteristics are investigated in five separate regions showing that crustal q depicts lower values in central compared to southern japan and a significant frequency dependence is observed in every region the source spectra follow the 2 model with higher stress drops for subcrustal earthquakes as compared with crustal ones while strong amplification effects dominate the site contributions for the surface sensors those for the borehole sensors are characterized by smaller variability nevertheless consistent with observations from deconvolution of borehole surface recording pairs downgoing wave effects are visible in the site contributions for many borehole stations finally the site amplification functions obtained at the surface are compared with surface to borehole s b and horizontal to vertical h v spectral ratios showing that the s b ratios generally provide better estimates of the horizontal amplification than the h v ratios due to amplification of the vertical component of ground motion

how variable is the number of triggered aftershocks aftershock activity depends at first order on the mainshock magnitude but also shows important fluctuations between shocks of equal magnitude we here investigate these fluctuations by quantifying them and by relating them to the mainshock stress drop and other variables for southern california earthquakes a method is proposed in order to only count directly triggered aftershocks rather than secondary aftershocks i e triggered by previous aftershocks and to only quantify fluctuations going beyond the natural poisson variability testing of the method subjected to various model errors allows to quantify its robustness it is found that these fluctuations follow a distribution that is well fitted by a log normal distribution with a coefficient of variation of about 1 0 to 1 1 a simple model is proposed to relate this observed dependence to mainshock stress drop variability

contrasting mechanisms of fluid flow through adjacent stratigraphic units during regional metamorphism south central maine usa the flow pattern of reactive metamorphic fluid through six outcrops of micaceous carbonate bearing sandstones from the vassalboro formation was determined by calculating and mapping fluid rock ratios for numerous samples within each outcrop the ratio of maximum to minimum measured fluid rock varied by factors of only 1 3 22 9 in each outcrop fluid flow was pervasive at metamorphic grades ranging from the biotite through the sillimanite zones average fluid rock ratio for the outcrops increases with increasing grade of metamorphism from 0 4 in the biotite zone to 1 4 in the sillimanite zone the flow pattern of reactive fluid through impure sandstones of the vassalboro formation was different at low and medium grades from fluid flow through the limestone member of the adjacent waterville formation in the biotite and garnet zones fluid flow through the waterville formation was channelized with channelways corresponding to individual lithologic layers that acted as metamorphic aquifers fluid rock ratios recorded by the aquifers are greater than those recorded by the intervening beds by factors of up to 50 60 at the highest grades of metamorphism sillimanite zone however flow through the waterville formation was as pervasive as through the vassalboro formation the waterville and vassalboro formations experienced the same metamorphic event the difference in pattern of fluid flow through the two formations therefore reflects the important control that lithology exerts on the permeability of rocks during metamorphism micaceous carbonate bearing sandstones evidently were more permeable than argillaceous carbonate rocks the greater permeability of the sandstones may result from a greater concentration of grain boundaries between unlike minerals in the rocks

source parameters of picoseismicity recorded at mponeng deep gold mine south africa implications for scaling relations abstract we investigate the source parameters of picoseismic and nanoseismic events m w 4 1 recorded with a high sensitivity seismic network at the mponeng gold mine in south africa to gain new insights into the scaling of small seismic events the japanese german underground acoustic emission research in south africa jaguars network composed of one three component 3c accelerometer sensitivity 50 hz to 25 khz and 8 acoustic emission ae sensors sensitivity 1 khz to 180 khz is located at a depth of 3268 m and covers the limited volume of approximately 300 300 300 m the ae sensors are calibrated with respect to the 3c accelerometer in the frequency band 400 hz 17 khz the waveform data of two datasets are analyzed 1 the aftershock sequence of an m w 1 9 event that occurred approximately 30 m from our network and 2 the postblasting activity recorded during working days located at a distance 90 m from the network at the exploitation level for the analysis we applied spectral fitting and spectral ratio methods the calculated values of m w range from 0 8 down to 4 1 with corner frequencies 0 8 khz 13 6 khz source sizes from 8 cm to 1 3 m we observe static stress drops ranging from 1 mpa to 10 0 mpa with apparent stresses of 0 01 mpa 1 00 mpa stress drops are independent of the moment suggesting self similar behavior in the analyzed magnitude range 4 1 m w

site response attenuation and source spectra of s waves along the guerrero mexico subduction zone acceleration spectra from nine earthquakes and up to 11 stations per earthquake are inverted to find the source spectra the site response and the quality factor q of s waves this method is applied to moderate earthquakes 4 0 0 8 hz does not follow a simple linear relation as observed in previous studies of attenuation in other regions when the source spectra are interpreted in terms of brune s model the stress drops obtained are less than 20 bars for the four larger events analyzed the site functions obtained indicate that although all the stations used are on rock the effect of the near surface geology caused important amplifications at some stations

selecting ground motion models developed for induced seismicity in geothermal areas we present a case study of the ranking and weighting of ground motion prediction equations gmpes for seismic hazard assessment of enhanced geothermal systems egss the study region is cooper basin australia where a hot fractured rock project was established in 2002 we test the applicability of 36 gmpes based on stochastic simulations previously proposed for use at egss each gmpe has a set of corresponding model parameters describing stress drop regional and local near surface attenuation to select suitable gmpes for cooper basin from the full set we applied two methods in the first seismograms recorded on the local monitoring network were spectrally analysed to determine characteristic stress and attenuation parameters in a second approach residual analysis using the log likelihood llh method was used to directly compare recorded and predicted short period response spectral accelerations the resulting ranking was consistent with the models selected based on spectral analysis with the advantage that a transparent weighting approach was available using the llh method region specific estimates of variability were computed with significantly lower values observed compared to previous studies of small earthquakes this was consistent with the limited range of stress drops and attenuation observed from the spectral analysis

a comparative geochemical study of pelitic schists and metamorphosed carbonate rocks from south central maine usa whole rock major element chemical analyses of progressively metamorphosed impure carbonate rocks and pelitic schists collected from the same metamorphic terrain reveal similarities and differences in the chemical response of these rock types to the metamorphic event relative to a constant aluminum reference frame both schist and carbonate exhibit no detectable change in their contents of fe mg ti si and ca with change in metamorphic grade carbonate rocks become progressively depleted in k and na with increasing grade of metamorphism while schists exhibit no statistically significant change in their contents of k and na both rock types become depleted in volatiles principally co2 and h2o with increasing grade

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

strain analysis of a northern apennine shear zone using deformed marble breccias abstract the alpi apuane region of the northern apennines appears to have been deformed within a large scale low angle shear zone with an overthrust sense of movement the presence of mineral stretching lineations folds progressively rotated into the x strain direction and schistosities which intersect the nappe boundaries at small angles suggest that a component of shear strain occurred during the deformation the strain ratios and orientations on two dimensional sections have been determined from deformed marble breccias reduction spots and oncalites data from three or more non perpendicular non principal sections have been combined to determine the finite strain ellipsoids at 33 sites within the shear zone the finite strains have been separated into components of simple shear longitudinal strain and volume change algebraic expressions have been derived and graphs constructed which enable components of and and and to be determined directly from a knowledge of strain ratio r within the shear zone and the angle between the principal strain direction and the shear zone boundary the alpi apuane data indicate that neither simple shear alone nor simple shear with volume change can satisfactorily explain the observed strains consideration of simple shear plus longitudinal strain leads to a general relationship in which the value of shear increases and the values of longitudinal strain change along a sw ne profile across the zone integration of the resulting shear strain distance curves gives a minimum displacement of 4 km within the shear zone combination of the finite strains with the total time of deformation known from k ar studies leads to average strain rates from 1 4 to 9 6 10 15 sec 1 a characteristic flat ramp flat geometry initially formed the boundaries of what was later to develop into the overthrust shear zone and deformation of the underlying crystalline basement is believed to have occurred by ductile shearing estimates of 21 crustal shortening for the region suggest that the crustal thickness prior to deformation was approximately 20 km in this part of the northern apennines

acadian metamorphism in the dunnage zone of southern quebec northern appalachians 40ar 39ar evidence for collision diachronism in new england the acadian orogen is divided into western and eastern metamorphic belts on the basis of contrasting pressure temperature p t paths peak metamorphism conditions and ages along strike correlations of structures indicate that rock units affected by devonian metamorphism and deformation in southern quebec belong to the western acadian belt and share the same tectonic evolution as in new england muscovite 40 ar 39 ar ages obtained from greenschist grade ordovician volcanic and plutonic rocks of the ascot complex in southern quebec indicate that acadian metamorphism and deformation peaked ca 380 375 ma ordovician muscovite ages of ca 462 ma are locally well preserved in the granitic intrusion of the ascot complex and provide constraints on the timing of island arc plutonism in the dunnage zone of southern quebec ordovician 40 ar 39 ar age spectra do not show important losses of radiogenic argon indicating that acadian metamorphism has been low grade with temperatures below the ar isotopic closure temperature proposed for muscovite acadian peak metamorphism is significantly younger and p t conditions of regional deformation have been lower in southern quebec than in amphibolite grade rocks of the western acadian belt of new england in the northern appalachians acadian metamorphism and deformation are attributed to devonian age crustal overthickening related to plate convergence the comparison of devonian tectonic fabrics in new england and southern quebec suggests that progression in the timing and p t conditions of acadian peak metamorphism in both areas are the result of the irregular geometry of the collision zone and of the northward migration of metamorphic and structural fronts along the orogen

temporal relationship between granite cooling and hydrothermal uranium mineralization at dalongshan in china a combined radiometric and oxygen isotopic study abstract a combined study using multi radiometric dating and oxygen isotopic geothermometry was carried out for mesozoic quartz syenite alkali feldspar granite and associated hydrothermal uranium mineralization at dalongshan in the middle lower yangtze valley of east central china radiometric dating of the quartz syenite yields a whole rock rb sr isochron age of 135 6 4 3 ma a zircon u pb isochron age of 132 9 2 2 ma and k ar ages of 126 2 118 3 and 94 4 ma for hornblende biotite and orthoclase respectively the alkali feldspar granite yields a whole rock rb sr isochron age of 117 3 3 3 ma a zircon u pb isochron age of 114 7 2 1 ma and k ar ages of 112 2 109 3 and 88 4 ma for hornblende biotite and orthoclase respectively oxygen isotope thermometry for both granites gives temperatures of 685 to 720 555 to 580 435 to 460 and 320 to 330 c for hornblende magnetite biotite and orthoclase respectively when paired with quartz the systematic differences among the ages by the different techniques on the different minerals are used to reconstruct the cooling history of the granite the results yield rapid cooling rates of 27 4 to 58 6 c ma from 800 to 300 c in the early stage but slow cooling rates of 6 3 to 7 2 c ma from 300 to 150 c in the late stage the regular sequence of oxygen isotope temperatures for the different quartz mineral pairs demonstrates that diffusion is a dominant factor controlling the closure of both radiometric and o isotopic systems during granite cooling pitchblende u pb isochron dating yields an uranium mineralization age of 106 4 2 9 ma which is younger than the age of the granite emplacement and thus considerably postdates the time of magma crystallization but is close to the closure time of the k ar system in the biotite this points to a close relationship between granite cooling and ore forming process it appears that hydrothermal mineralization took place in the stage of slow cooling of the granite whereas the rapid cooling of the granite was concurrent with the migration of hydrothermal fluids along fault structures therefore the activity of the ore forming hydrothermal system is temporally dictated by the cooling rates of the granite and may lag about 25 to 30 ma behind the crystallization timing of associated granite

source scaling of inland crustal earthquake sequences in japan using the s wave coda spectral ratio method we estimate corner frequencies and stress drops for 298 events ranging from m w 3 2 7 0 in 17 inland crustal earthquake sequences in japan to investigate the source scaling and variation in stress drops we obtain the source spectral ratio from observed records by the s wave coda spectral ratio method the advantage of using the s wave coda is in obtaining much more stable source spectral ratios than using direct s waves we carefully examine the common shape of the decay of coda envelopes between event pair records the corner frequency and stress drop are estimated by modeling the observed source spectral ratio with the omega square source spectral model we investigate the dependences of stress drops on some tectonic effects such as regionality focal mechanism and source depth the principal findings are as follows 1 a break in self similar source scaling is found in our dataset events larger than m w 4 5 show larger stress drops than those of smaller events 2 stress drops of aftershocks are mostly smaller than those of mainshocks in each sequence 3 there are no systematic differences between stress drops of events occurring inside and outside the niigata kobe tectonic zone in japan 4 clear dependence of the faulting type on stress drops cannot be seen 5 stress drops of aftershocks depend on their source depth 6 the crack size obtained from the corner frequency corresponds to the total rupture area of heterogeneous slip models for large events

earthquake in a maze compressional rupture branching during the 2012 mw 8 6 sumatra earthquake seismological observations of the 2012 moment magnitude 8 6 sumatra earthquake reveal unprecedented complexity of dynamic rupture the surprisingly large magnitude results from the combination of deep extent high stress drop and rupture of multiple faults back projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system with relatively slow rupture speed the east southeast west northwest ruptures add a new dimension to the seismotectonics of the wharton basin which was previously thought to be controlled by north south strike slip faulting the rupture turned twice into the compressive quadrant against the preferred branching direction predicted by dynamic coulomb stress calculations orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure insensitive strength of the deep oceanic lithosphere

a tectonic model for the late paleozoic of southeastern new england hornblende and biotite sup 40 ar sup 39 ar age spectra from rocks in south central connecticut help define a permian triassic cooling curve for the area together with petrologic and structural information a time temperature pressure strain path is established similar data for the narragansett basin in rhode island and massachusetts allow correlation of the late paleozoic histories of the two areas together these data suggest that in the late paleozoic south central new england was part of a fold thrust belt and the narragansett basin was a retroarc foreland basin nw se compression during the final assembly of pangaea resulted in se directed thrusting causing the development of clastic wedges in adjacent rhode island and massachusetts in the late carboniferous early permian a clockwise rotation of this deformation from nw to nne led to northward underthrusting and concomitant uplift of both eastern connecticut and rhode island in the permian and triassic

separation of source and site effects in ground motions recorded in the village of onna during aftershocks of the 2009 april 6 mw 6 1 l aquila earthquake this article has been accepted for publication in geophysical journal internationa the authors 2017 published by oxford university press on behalf of the royal astronomical society all rights reserved

rapid estimation of earthquake source and ground motion parameters for earthquake early warning using data from a single three component broadband or strong motion sensor we propose a new algorithm to rapidly determine earthquake source and ground motion parameters for earthquake early warning eew this algorithm uses the acceleration velocity and displacement waveforms of a single three component broadband bb or strong motion sm sensor to perform real time earthquake noise discrimination and near far source classification when an earthquake is detected the algorithm estimates the moment magnitude m epicentral distance and peak ground velocity pgv at the site of observation the algorithm was constructed by using an artificial neural network ann approach our training and test datasets consist of 2431 three component sm and bb records of 161 crustal earthquakes in california japan and taiwan with 3 1 m 7 6 at 115 km first estimates become available at t 0 0 25 s after the p pick and are regularly updated we find that displacement and velocity waveforms are most relevant for the estimation of m and pgv while acceleration is important for earthquake noise discrimination including site corrections reduces the errors up to 10 the estimates improve by an additional 10 if we use both the vertical and horizontal components of recorded ground motions the uncertainties of the predicted parameters decrease with increasing time window length t 0 larger magnitude events show a slower decay of these uncertainties than small earthquakes we compare our approach with the c algorithm and find that our prediction errors are around 60 smaller however in general there is a limitation to the prediction accuracy an eew system can provide if based on single sensor observations

accurate estimation of seismic source parameters of induced seismicity by a combined approach of generalized inversion and genetic algorithm application to the geysers geothermal area california the accurate determination of stress drop seismic efficiency and how source parameters scale with earthquake size is an important issue for seismic hazard assessment of induced seismicity we propose an improved non parametric data driven strategy suitable for monitoring induced seismicity which combines the generalized inversion technique together with genetic algorithms in the first step of the analysis the generalized inversion technique allows for an effective correction of waveforms for attenuation and site contributions then the retrieved source spectra are inverted by a non linear sensitivity driven inversion scheme that allows accurate estimation of source parameters we therefore investigate the earthquake source characteristics of 633 induced earthquakes mw 2 3 8 recorded at the geysers geothermal field california by a dense seismic network i e 32 stations more than 17 000 velocity records we find a non self similar behavior empirical source spectra that require an source model with 2 to be well fit and small radiation efficiency sw all these findings suggest different dynamic rupture processes for smaller and larger earthquakes and that the proportion of high frequency energy radiation and the amount of energy required to overcome the friction or for the creation of new fractures surface changes with earthquake size furthermore we observe also two distinct families of events with peculiar source parameters that in one case suggests the reactivation of deep structures linked to the regional tectonics while in the other supports the idea of an important role of steeply dipping faults in the fluid pressure diffusion

geochronology at the namew lake ni cu orebody flin flon area manitoba canada thermal history of a metamorphic terrane intermediate composition orthogneisses of the southward extension of the flin flon greenstone belt surround the ultramafic host rock of the namew lake ni cu deposit in northern manitoba the gneiss

rates of processes in magmatic arcs implications for the timing and nature of pluton emplacement and wall rock deformation abstract the construction of arcs and in many cases the emplacement of plutons occur in tectonically active regions it is critical therefore to evaluate the rates of structural and magmatic processes when trying to understand the evolution of arcs and the associated pluton wall rock systems our best estimates of average rates or durations of processes in shallow to moderate level arc environments are the following 1 crystal growth rates in magma of 10 4 cm year 1 2 growth rates of metamorphic porphyroblasts between 10 5 and 10 2 cm year 1 3 long term magma supply rates of 10 1 km 3 year 1 and short term rates of up to 350 km 3 year 1 4 diapiric ascent rates for mafic plutons of 1 3 m year 1 5 cooling of plutons to ambient wall rock temperatures in 10 5 10 6 years 6 final crystallization of plutons in a small fraction of the time needed for complete cooling 7 fault displacements of 3 cm year 1 8 development of cleavages in fault zones in less than 10 6 years at strain rates of 10 13 s 1 or higher and 9 the development of regional cleavages in 10 6 years at strain rates of 10 14 s 1 these rates indicate that processes operating in magmatic arcs are relatively rapid pluton emplacement cleavage development etc occur over time spans of tens of thousands to no more than a few million years however the rate of ascent and crystallization of plutons at shallow levels is generally shorter than that needed to get large displacements on faults or widespread cleavages developed at deeper levels or in zones undergoing faster strain rates the time spans of the various processes approach one another thus plutons with otherwise similar characteristics emplaced in regions undergoing fast strain rates or at deeper crustal levels may appear quite different structurally from those emplaced at shallow levels or in regions undergoing slower strain rates comparison of these data also suggests that the rate at which wall rock deforms is the limiting factor controlling the rates of other structural processes during emplacement of plutons unless fast strain rates or multiple deformation mechanisms are considered thus emplacement mechanisms that rely on the transport of magma over 10 5 to 10 6 years are favored and need further consideration finally we argue that the structural and other characteristics of pluton wall rock systems will depend on rates of various processes involved and that these rates at the very least influence and sometimes invalidate the timing criteria previously published by us and others

finder v 2 improved real time ground motion predictions for m2 m9 with seismic finite source characterization recent studies suggest that small and large earthquakes nucleate similarly and that they often have indistinguishable seismic waveform onsets the characterization of earthquakes in real time such as for earthquake early warning therefore requires a flexible modeling approach that allows a small earthquake to become large as fault rupture evolves over time here we present a modeling approach that generates a set of output parameters and uncertainty estimates that are consistent with both small moderate m6 5 and large earthquakes m6 5 as is required for a robust parameter interpretation and shaking forecast our approach treats earthquakes over the entire range of magnitudes m2 as finite line source ruptures with the dimensions of small earthquakes being very small 100 m and those of large earthquakes exceeding several tens to hundreds of kilometres in length the extent of the assumed line source is estimated from the level and distribution of high frequency peak acceleration amplitudes observed in a local seismic network high frequency motions are well suited for this approach because they are mainly controlled by the distance to the rupturing fault observed ground motion patterns are compared with theoretical templates modeled from empirical ground motion prediction equations to determine the best line source and uncertainties our algorithm extends earlier work by bose et al for large finite fault ruptures this paper gives a detailed summary of the new algorithm and its offline performance for the 2016 m7 0 kumamoto japan and 2014 m6 0 south napa california earthquakes as well as its performance for about 100 real time detected local earthquakes 2 2 m 5 1 in california for most events both the rupture length and the strike are well constrained within a few seconds 10 s of the event origin in large earthquakes this could allow for providing warnings of up to several tens of seconds the algorithm could also be useful for resolving fault plane ambiguities of focal mechanisms and identification of rupturing faults for earthquakes as small as m2 5

earthquake scaling characteristics and the scale in dependence of seismic energy to moment ratio insights from kik net data in japan 1 we investigate earthquake source characteristics and scaling properties using the results of a spectral inversion of more than 29 000 accelerometric borehole recordings from 1 826 earthquakes mjma 2 7 8 throughout japan we find that the calculated source spectra can be well characterized by the omega square model and show on average self similar scaling over the entire magnitude range with median stress drops of 1 1 and 9 2 mpa for crustal and subcrustal events respectively the seismic energy to moment ratio as theoretically expected if the omega square model is valid shows a strong dependency on stress drop only which in conjunction with data selection practice in some studies to cope with limited recording bandwidth can explain the often observed apparent scale dependence our observations suggest that there is no significant deviation from similarity of the energy radiation in the investigated magnitude range and that the observed scatter is mainly related to the scatter in stress drop

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

oxygen isotope geochemistry of hydrothermally altered synmetamorphic granitic rocks from south central maine usa hydrothermally altered mesozonal synmetamorphic granitic rocks from maine have whole rock 18o smow values 10 7 to 13 8 constituent quartz feldspar and muscovite have 18o in the range 12 4 to 15 2 10 0 to 13 2 and 11 1 to 12 0 respectively mean values of q f 18oquartz 18ofeldspar 2 4 and q m 18oquartz 18omuscovite 3 3 are remarkably uniform standard deviations of both are 0 2 measured q f and q m values demonstrate that the isotopic compositions of the minerals are altered from primary magmatic 18o values but that the minerals closely approached oxygen isotope exchange equilibrium at subsolidus temperatures analyzed muscovites have d smow values in the range 65 to 82 feldspars in the granitic rocks are mineralogically altered to either a muscovite calcite b muscovite calcite epidote c muscovite epidote or d muscovite only a consistent relation exists between the assemblage of secondary minerals and the oxygen isotope composition of whole rocks quartz and feldspar rocks with assemblage a have whole rock 18o 12 1 and contain quartz and feldspar with 18o 13 8 and 11 4 respectively rocks with assemblages b c and d have whole rock 18o 11 4 and contain quartz and feldspar with 18o 13 1 and 11 0 respectively the correlation suggests that the mineralogical alteration of the rocks was closely coupled to their isotopic alteration three mineral thermometers in altered granite suggest that the hydrothermal event occurred in the temperature range 400 150 c 100 150 c below the peak metamorphic temperature inferred for country rocks immediately adjacent to the plutons calculations of mineral fluid equilibria indicate that samples with assemblage a coexisted during the event with co2 h2o fluids of text x text co text 2 0 03 0 13 and 18o 10 8 to 12 2 while samples with assemblages b c or d coexisted with fluids of text x text co text 2 leqslant 0 03 and 18o 9 4 to 10 1 compositional variations of the hydrothermal fluids were highly correlated fluids enriched in co2 were also enriched in 18o because co2 was added to the granites during hydrothermal alteration and because fluids enriched in co2 were enriched in 18o some or all of the variation in 18o of altered granites may have been caused by addition of 18o to the rocks during the hydrothermal event the source of both the co2 and 18o could have been high 18o metasedimentary country rocks the inferred change in isotopic composition of the granites is consistent with depletion of the metacarbonate rocks in 18o close to the plutons and with large volumes of fluid that were inferred from petrologic data to have infiltrated the metacarbonate rocks during metamorphism a close approach of minerals to oxygen isotope exchange equilibrium in altered mesozonal rocks from maine is in marked contrast to hydrothermally altered epizonal granites whose mineral commonly show large departures from oxygen isotope exchange equilibrium the difference in oxygen isotope systematics between altered epizonal granites and altered mesozonal granites closely parallels a differences between their mineralogical systematics both differences demonstrate the important control that depth exerts on the products of hydrothermal alteration deeper hydrothermal events occur at higher temperature and are longer lived minerals and fluid have sufficient time to closely approach both isotope exchange and heterogeneous chemical equilibrium shallower hydrothermal events occur at lower temperatures and are shorter lived generally there is insufficient time for fluid to closely approach equilibrium with all minerals