slip system domains 2 kinematic aspects of fabric development in polycrystalline aggregates abstract in the first paper of the present series cobbold and gapais 1986 we develop theoretical models of plane strain domainal deformation by slip along inextensible and indestructible fibres for such extreme mechanical conditions we show that deformation is largely controlled by kinematic factors we use our models to explain domainal patterns of natural slip systems including bedding and foliation planes faults ductile shear zones and lattice planes the present paper focusses on kinematic aspects of fabric development in polycrystalline aggregates a three dimensional kinematic model is developed it reveals that common quartz fabrics may develop domainally by reorientation and selection of inextensible slip directions a axes or slip planes with initially random orientation stable orientations of slip directions are close to both surfaces of no finite extension and orientations of large amount of shear we explain 1 1 common patterns of quartz a and c axis fabrics e g small circles and crossed girdles 2 2 characteristic differences between fabric patterns according to the shape of the finite strain ellipsoid 3 3 development of asymmetric fabrics during non coaxial deformation histories this last process involves selective destruction or replacement of certain orientation domains so that a preferred orientation of slip lines develops close to the bulk shear direction rotation recrystallization is shown to be an efficient natural selection mechanism the models also account for many microstructural features found in oriented polycrystalline rocks especially 1 1 alternating band like or kink like domains of twinned preferred orientations 2 2 individual grains or clusters of grains with retort like shapes and extensive recrystallisation at boundaries 3 3 small scale shear bands formed by strain partitioning and shear localization

microstructures and c axis fabrics indicative of quartz dissolution in sheared quartzites and phyllonites abstract quartzites sheared in low metamorphic grade shear zones that extend along the contact with migmatitic gneissic complexes in the quadrilatere ferifero region southeastern brazil show quartz microstructures indicating deformation by dissolution dissolution occurred adjacent to the foliation planes preferentially in quartz porphyroclasts oriented with their 0001 planes parallel to the foliation dissolution worked as an efficient mechanism to remove porphyroclast edges smoothing foliations and enabling strain accommodation both dissolution and crystal plasticity were competitive crystallographically controlled processes operating in different domains of the evolving microstructure dissolution occurred along the foliation planes while isovolume crystal plasticity and accompanying recrystallization operated essentially in the quartzose domains between folia phyllonites formed in the most strained domains of the shear zones fine grained quartz grains in phyllonites show uncommon c axis fabrics c axis oriented at low angles to the stretching lineation which were interpreted to form either by direct reprecipitation or by residual concentration of grains unfavourably orientated to undergo dissolution domainal c axis fabrics reflect a deformation partitioning path with increasing participation of solution transfer strengthening c axis maxima at low angles with the stretching lineation at the expense of crystal plastic processes during progressive phyllonitization

source radiation invariant property of local and near regional shear wave coda application to source scaling for the mw 5 9 wells nevada sequence 1 this study documents another unique property of local and regional shear wave coda that scattering in the earth s crust averages out source heterogeneities such as focal mechanism and directivity we consider two recent events which exhibited significant source directivity the first an mw 4 2 oakland hills california strike slip event on july 20 2007 resulted in uncharacteristically large amounts of damage in the montclair and south berkeley neighborhoods along strike and north west of the hypocenter but almost no damage to the south east the second event the mw 5 9 wells nevada dip slip event of february 21 2008 was well recorded by the earthscope transportable array usarray and determined to exhibit south west directivity we conclude with an example of corner frequency fc estimates from the wells sequence which showcase the coda s low variance and find that scaling is non self similar suggesting a change in dynamics between the mainshock and aftershocks

aleutian terranes from nd isotopes nd isotope ratios substantiate the identification of oceanic crustal terranes within the continental crustal basement of the aleutian island arc the oceanic terranes are exposed in the westernmost aleutians but to the east they are completely buried by isotopically distinct arc volcanic rocks analogous oceanic terranes may be important components of the terrane collages that comprise the continents

magmatic evolution of semisopochnoi island alaska trace element and isotopic constraints semisopochnoi has erupted a tholeiitic suite of moderately evolved lavas sio 2 50 65 zr 64 250 ppm la 10 60x chondrites whose bulk rock chemistry and phenocryst mineralogy are generally compatible with an important role for fractional crystallization in controlling the overall evolution of the suite trace element data however are not consistent with crystal fractionation operating alone instead a variety of plots involving incompatible elements or ratios among them demonstrate that simple mixing between basaltic and silicic components can reproduce the essential aspects of the trace element variations and must have been operative as well we are unable to distinguish between a silicic end member represented by residual dacitic liquid like one of the analyzed lavas therefore implying magma mixing and one consisting of pre existing silicic crustal rocks therefore implying assimilation variations in sr and nd isotopic compositions are very limited 143 nd 144 nd 0 51225 0

aleutian tholeiitic and calc alkaline magma series i the mafic phenocrysts diagnostic mafic silicate assemblages in a continuous spectrum of aleutian volcanic rocks provide evidence for contrasts in magmatic processes in the aleutian arc crust tectonic segmentation of the arc exerts a primary control on the variable mixing fractional crystallization and possible assimilation undergone by the magmas end members of the continuum are termed calc alkaline ca and tholeiitic th ca volcanic rocks e g buldir and moffett volcanoes have low feo mgo ratios and contain compositionally diverse phenocryst populations indicating magma mixing their ni and cr rich magnesian olivine and clinopyroxene come from mantle derived mafic olivine basalts that have mixed with more fractionated magmas at mid to lower crustal levels immediately preceding eruption high al amphibole is associated with the mafic end member in contrast th lavas e g okmok and westdahl volcanoes have high feo mgo ratios and contain little evidence for mixing evolved lavas represent advanced stages of low pressure crystallization from a basaltic magma these lavas contain groundmass olivine fo 40 50 and lack ca poor pyroxene aleutian volcanic rocks with intermediate feo mgo ratios are termed transitional tholeiitic tth and calc alkaline tca tca magmas are common e g moffett adagdak great sitkin and kasatochi volcanoes and have resulted from mixing of high al basalt with more evolved magmas they contain amphibole high and low al or orthopyroxene or both and are similar to the japanese hypersthene series tth magmas e g okmok and westdahl contain orthopyroxene or pigeonite or both and show some indication of upper crustal mixing they are mineralogically similar to the japanese pigeonite series high al basalt lacks mg rich mafic phases and is a derivative magma produced by high pressure fractionation of an olivine tholeiite the low pressure mineral assemblage of high al basalt results from crystallization at higher crustal levels

seismic moments local magnitudes and coda duration magnitudes for earthquakes in central california onscale seismograms recorded at stations in the u s geological survey s usgs central california seismic network calnet have been used to estimate the seismic moment m and local magnitude ml for earthquakes of 1 ml 4 located on the san juan bautista and parkfield sections of the san andreas fault the coyote lake section of the calaveras fault the sargent fault and near livermore these data together with m and ml estimates for 4 ml 6 earthquakes in these areas cannot be fit with a single linear log m versus ml relation rather the data are consistent with log m 1 5 ml 16 for 3 ml 6 with log m 1 2 ml 17 for 1 1 2 ml 3 1 2 and with a slope of to 1 fro 1 2 ml 1 1 2 whereas usgs coda duration magnitude md is consistent with ml for 1 1 2 ml 3 md is larger than ml at ml 1 1 2 and smaller than ml at ml 3 log m can be estimated to a precision of 0 2 for 1 md 3 1 2 earthquakes in central california by applying log m 1 2 md 17 to the md that have been routinely published by the usgs

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

the competition between rates of deformation and solidification in syn kinematic granitic intrusions resolving the pegmatite paradox abstract while fully crystallized granites rich in feldspar generally serve to strengthen the continental crust their precursor melts are assumed to be important agents of crustal weakening many syn tectonic granitic pegmatites are deformed within shear zones but ubiquitously preserve undeformed primary magmatic textures implying that they were largely molten during shearing yet the shapes of pegmatite bodies indicate that they deformed with a greater competence than their surroundings this co located pair of material behaviours is paradoxical we interpret field relationships in a typical pegmatite shear zone association torrisdale nw scotland and propose a mechanism by which syn tectonic granitic melts may in effect act as competent bodies while not yet fully crystallized competence was rapidly increased by preferential crystallization on intrusion margins that served to encapsulate residual melt inside stiff rinds further crystallization may have been pulsed as the concentrations of crystallization inhibitors fluxes increased in residual fluids postulating the existence of initial stiff rinds also consistent with modern estimates for rates of feldspar crystallization cms yr from undercooled hydrous silicic magma to form pegmatites these greatly outpace strain rate estimates for shear zones thus fully liquid granitic melts may only be present fleetingly and have little opportunity to weaken deforming crust before crystallization begins

quartz c axes parallel to stretching directions in very low grade metamorphic rocks abstract quartz preferred orientations with c axes parallel to stretching directions are widespread in slates phyllites and very low grade schists of the south island new zealand in general these rocks lack evidence for plastic deformation of quartz and often preserve the original clastic quartz which naturally tends to be elongate parallel to the c axis the c axis preferred orientation can be explained therefore by mechanical rotation of clastic grains during deformation so that long axes became parallel to the stretching direction plastic deformation does however play a role in some very quartz rich layers which display a preferred orientation due to basal slip with c axes at high angles to the stretching direction solution transfer is important in enhancing the contrasts between pelitic and quartz rich lithologies but its role in producing c axis preferred orientations by competitive anisotropic growth or solution seems important only in slickenfibres and in fibrous quartz veins of shear zones where quartz displays very strong preferred orientations with c axes parallel to the local stretching direction in contrast the non fibrous quartz pressure shadows in some muscovite rich layers display a c axis preferred orientation similar to adjacent quartz rich sand layers and it probably results from nucleation of pressure shadow quartz on pre existing mechanically oriented quartz clasts

using p s amplitude ratios for seismic discrimination at local distances we used a dense seismic network to test the p s amplitude ratio discriminant for earthquakes and explosions at distances from 20 to 200 km in a complex tectonic setting we used data from several hundred seismic stations in northern wyoming to observe 22 earthquakes 37 mining blasts and 24 borehole shots and compared their p s amplitude ratios frequencies of 6 8 hz and above achieved the best discrimination results for single shot borehole explosions whereas 6 8 and 8 10 hz passbands were best for mining blasts the p s method appears valid for 50 200 km but fails at distances 50 km geologic heterogeneities and path effects have a large effect on amplitude measurements even after magnitude and distance amplitude corrections are applied geologic boundaries between source and receiver that cause sharp lateral discontinuities in seismic velocity can alter the measured p s ratio to the point that an event could be misidentified the source geology is a factor as well with noticeable amplitude differences between shots in bedrock and shots in sediment we tested the discrimination performance of the average log p s values of a network of seismometers which should reduce the discrimination errors caused by these heterogeneities relative to a single station by bootstrapping the single station measurements over varying sample sizes we found that averaging three or four stations achieved significantly better discrimination than just one or two stations finally we corrected the signal amplitude to remove prephase noise to improve p s discrimination results this shows promise for improving event discrimination with only simple corrections online material table of event information and figure showing waveforms overlaid with amplitude windows

tectonic controls on tholeiitic and calc alkaline magmatism in the aleutian arc the tectonic position of aleutian arc volcanic centers and their magmatic differentiation trends calc alkaline or tholeiitic appear to correlate from 160 w to 175 e the volcanoes form four major arc segments that coincide with earthquake aftershock zones and major geographic features on both the upper and lower plates the tholeiitic volcanoes are large primarily basaltic centers that occur between or at the end of segments where magmas can more easily reach the surface and undergo shallow closed system differentiation the calc alkaline volcanoes are smaller more andesitic centers that occur in the middle of segments where transit through the upper plate is apparently more difficult differentiation is deeper and the intrusive to extrusive ratios are higher than in the tholeiitic centers the chemistry of the least differentiated basalts at both types of centers is similar and suggests a common parent magma probably derived from mantle peridotite conditions for the derivation of the two trends through crystal fractionation support the proposed model the tholeiitic magmas show characteristics i e no hydrous phenocrysts fe enrichment trend parallel ree patterns vitrophyric and esites and dacites consistent with low pressure high temperature crystallization in large shallow magma chambers the calc alkaline magmas show characteristics i e some hydrous phenocrysts no fe enrichment trend nonparallel rare earth patterns porphyritic lavas consistent with higher pressure and lower temperature of crystallization than the tholeiitic series tertiary plutons also show both calc alkaline and tholeiitic trends and appear to be chemically similar to the quaternary volcanoes the larger plutons are calc alkaline and probably represent the extensive 1002 km magma chambers of the small calc alkaline volcanoes the small shallow tholeiitic plutons complement the large tholeiitic volcanoes and reflect the greater percent of extrusive rocks in the tholeiitic series

the influence of amphibole fractionation on the evolution of calc alkaline andesite and dacite tephra from the central aleutians alaska petrologic studies of tephra from kanaga adak and great sitkin islands indicate that amphibole fractionation and magma mixing are important processes controlling the composition of calc alkaline andesite and dacite magmas in the central aleutians amphibole is ubiquitous in tephra from kanaga and adak islands whereas it is present only in a basaltic andesite pumice from great sitkin dacitic tephra from great sitkin do not contain amphibole hornblende dacite tephra contain hb plag ox opx cpx phenocrysts with simple zoning patterns suggesting that the dacites evolved in isolated magma chambers andesitic tephra from adak contain two pyroxene and hornbelende populations and reversely zoned plagioclase indicating a more complex history involving mixing and fractional crystallization mass balance calculations suggest that the andesitic tephra may represent the complements of amphibole bearing cumulate xenoliths both formed during the evolution of high al basalts the presence of amphibole in andesitic and dacitic tephra implies that aleutian cale alkaline magmas evolve in the mid to lower crust under hydrous 4 wt h2o and oxidizing ni nio conditions amphibole bearing andesites and pyroxene bearing dacites from great sitkin indicates fractionation at several levels within the arc crust despite its absence in many calc alkaline andesite and dacite lavas open system behavior involving amphibole fractionation can explain the trace element characteristies of lavas found on adak island neither open nor closed system fractionation involving a pyroxene bearing assemblage is capable of explaining the trace element concentrations or ratios found in the adak suite we envision a scenario where amphibole was initially a liquidus phase in many calc alkaline magmas but was later replaced by pyroxenes as the magmas rose to shallow levels within the crust the mineral assemblage in these evolved lavas reflects shallow level equilibration of the magma whereas the trace element chemistry provides evidence for a earlier amphibole bearing mineral assemblage

small magnitude earthquakes in north central wyoming recorded during the bighorn arch seismic experiment we took advantage of a high density seismic array deployed coincident with usarray to study small magnitude seismicity patterns in northern wyoming we detected and located a total of 89 earthquakes ranging in magnitude from 0 5 to 2 4 during the six month period of april to september 2010 most events were located shallower than 25 km in the crust with a few events as deep as 39 km and one very deep earthquake below the moho at 63 km we also detected and recorded 1563 mining explosions in the area we computed focal mechanism solutions for 14 earthquakes and observed dominantly normal faulting stress inversions obtained from these focal mechanisms show extension oriented n20 e that matches borehole breakout data collected in the area though wastewater injection wells were active in the region we see no evidence of induced seismicity in this catalog the seismicity pattern shows earthquakes occurring beneath areas of high topography in the bighorn and owl creek mountain ranges this may indicate a preference to slip on pre existing weaknesses created during mountain building the absence of earthquakes between 39 and 63 km depths represents an aseismic zone in the lower crust that may indicate a rheological change between brittle and ductile behavior in the crust and a strong mantle capable of brittle failure online material maps of earthquake catalogs figures of depth versus misfit time of day histograms for earthquakes and mine explosions earthquake density and location of class ii disposal wells relative to earthquakes

quartz fabric transition in a cooling syntectonic granite hermitage massif france abstract the hermitage granite situated in the northwest massif central france is a syntectonic hercynian leucogranite emplaced along an active transcurrent shear zone during emplacement and cooling the progressive deformation is marked by the development of a primary homogeneous foliation gradually affected by ductile shear bands c s mylonites increase in strain heterogeneity during cooling corresponds to a change of dominant deformation mechanism of the quartz phase from grain growth and migration recrystallization to intracrystalline a slip and rotation recrystallization migration recrystallization is characterized by preferred orientations of c axes close to the principal extension direction we discuss relevant deformation mechanisms and rheological implications for syntectonic plutons in particular we argue that the transitions between homogeneous and heterogeneous accumulation of strain cannot generally be correlated with transition between magmatic and solid state flow

single station spectral discrimination using coda waves spectral discrimination methods applied at regional distances are based on the observation that there is a difference in the frequency content of the seismic waves radiated from the source region of earthquakes and explosions we have investigated a spectral discrimination method that exploits the scattered energy contained in the event codas of seismograms to measure the relative source excitation of earthquakes and explosions as a function of frequency key strengths of the coda method include the following 1 it is not affected by source radiation pattern because the scattering process averages the radiation over the focal sphere 2 path corrections are not required with the coda method because coda waves are scattered throughout a common crustal volume 3 it can be successfully applied using data from only a single station and 4 it can be successfully applied using data with clipped direct arrivals to implement the coda method we first estimate a type curve which represents the average shape of all the individual coda decay curves for a particular frequency band the shape of the type curve as well as the shape of all individual coda decay curves is controlled by the scattering and attenuation properties of the crustal volume sampled by the coda waves a common path effect the amplitude of the type curve is not defined and we arbitrarily adjust it to have a zero mean the amplitude difference between an individual event coda decay curve and the type curve provides a relative measure of the event s source size within the particular frequency band we define this amplitude difference as the relative source factor our approach exploits all of an event s usable coda for each spectral measurement thus providing a more stable measure of relative source size than could be obtained from using a predefined fixed length time window analysis of 27 nevada test site explosions and 15 southern great basin earthquakes 3 1 m 4 7 shows that the source factor difference between the 0 5 to 1 and 2 to 4 hz bands plotted against the 1 to 2 hz source factor is a stable event discriminant the method reliably distinguishes small explosions from small earthquakes 3 0 m 3 5 even if the explosions are overburied because the coda method requires only one seismic station we believe that it would be especially useful in identifying small clandestine underground nuclear tests that occur far from established networks

lattice preferred orientations of late variscan granitoids derived from neutron diffraction data implications for magma emplacement mechanisms the lattice preferred orientation lpos of two late variscan granitoids the meissen monzonite and the podlesi dyke granite were determined from high resolution time of flight neutron diffraction patterns gained at the diffractometer skat in dubna russia the results demonstrate that the method is suitable for the lpo analysis of polyphase relatively coarse grained 0 1 6 mm rocks the meissen monzonite has a prominent shape preferred orientation spo of the non equidimensional minerals feldspar mica and amphibole whereas spo of the podlesi granite is unapparent at the hand specimen scale the neutron diffraction data revealed distinct lpos in both granitoids the lpo of the non equidimensional minerals feldspar mica and amphibole developed mainly during magmatic flow in the case of the meissen monzonite the magmatic flow was superimposed by regional shear tectonics which however had no significant effect on the lpos in both samples quartz shows a weak but distinct lpo which is atypical for plastic deformation and different in the syn kinematic meissen monzonite and the post kinematic podlesi granite we suggest that first of all the quartz lpo of the meissen monzonite is the result of oriented growth in an anisotropic stress field the quartz lpo of the podlesi granite which more or less resembles a deformational lpo in the flattening field of the local strain field developed during magmatic flow whereby the rhombohedral faces of the quartz crystals adhered to the 010 faces of aligned albite and to the 001 faces of zinnwaldite due to shape anisotropy of their attachments the quartz crystals were passively aligned by magmatic flow thus magmatic flow and oriented crystal growth are the major lpo forming processes in both granitoids for the meissen monzonite the solid state flow was too weak to cause significant crystallographic re orientation of the minerals aligned by magmatic flow finally the significance of our results for the evaluation of the regional tectonic environment during magma emplacement is discussed the discussion on the regional implications of the more methodologically oriented results provides the basis for future more regionally aimed studies in view of the fabric characteristics of such plutons and their developing mechanisms

empirical dependence of seismic ground velocity on the weight of explosives shotpoint site condition and recording distance for seismic refraction data in this study we have constructed an empirical least squares model for maximum seismic ground velocity vertical component as a function of source size and distance from explosions in drillholes and bodies of water this model is intended in part for use in designing explosion seismic experiments in order to produce acceptable signal to noise ratios at larger distances 10 km and to avoid damaging human structures at smaller distances 1 km data consist of velocities recorded by 120 portable seismographs from 159 shots fired by the u s geological survey in alaska and arizona results show that maximum ground velocity amplitude not necessarily first arrival amplitude decreases with distance and the functional dependence changes with distance for example at 3 km amplitudes decrease as r 2 but at 73 km they decrease as r 1 results also show a strong dependence on site conditions at the shotpoint for example a drillhole shot in wet alluvium produces amplitudes that are four times larger than a drillhole shot in dry alluvium ground velocities are proportional to the square root of the weight of explosives

seismic yield determination of soviet underground nuclear explosions at the shagan river test site summary a study of p and lg based source size estimators has been conducted for 101 presumed underground nuclear explosions at the shagan river test site near semipalatinsk ussr a systematic variation in the relative patterns across the test site has been observed when comparing the p wave estimators world wide mb and ulm and the lg based observations rms lg determined from norsar and grafenberg array recordings these variations correlate well with geological features determined from satellite imagery and suggest in particular that the northeast and southwest portions of the test site divided by the chinrau fault are characterized by distinct geophysical properties a difference in m p mlg bias of as much as 0 15 magnitude units exists between these two subareas available data indicate that the mlg observations are very consistent with published yields and suggest that the magnitude yield relationship for p wave based estimators can be significantly improved by introducing regional bias corrections we have determined such corrections for three subareas of the test site and used the corrected mh and ym observations in combination with the lg data in a weighted averaging scheme to arrive at yield estimates for all events in the database for the explosion of 1988 september 14 we obtain yield estimates from the three estimators ranging from 106 to 118 kt which is consistent with the independently derived estimates of 115 122 kt quoted by sykes ekstrom 1989 a further assessment of the validity of our results would require access to independently measured yields of additional explosions

depths and water content of magma chambers in the aleutian and mariana island arcs on pseudoternary diagrams locations of experimentally produced melt compositions that coexist with plagioclase and anhydrous mafic minerals vary as functions of pressure a geobarometer and water content a geohygrometer projection of rock compositions onto diagrams allows constraints to be placed on magma chamber depths and meltwater content application of the experimentally calibrated geobarometer and gehygrometer to aleutian and mariana rock suites suggests aleutian magma chambers to be at depths of 7 to 17 km pressures from 2 to 5 kbar and meltwater content of andesites near 2 wt mariana magma chambers are at shallow depths pressure less than 2 kbar and their water content is less than 2 wt probably near 1 wt magma chamber depths can be interpreted to be controlled by density differences between crystallizing magmas and crust which in turn may be controlled by crustal thermal structure differences in water content are correlated with amounts of sediment incorporated into basaltic magmas formed near the subducting oceanic slab

the stability of rms lg measurements and their potential for accurate estimation of the yields of soviet underground nuclear explosions data on underground nuclear explosions have recently become available from modern digital seismic stations installed within the soviet union and china observations of root mean square rms lg wave signals for soviet underground nuclear explosions at the shagan river test site in east kazakhstan show that the relative amplitudes of the rms signals at stations in norway the ussr and china are very similar for different explosions the standard deviation of the differences being only about 0 03 in logarithmic units i e magnitude units this is consistent with earlier observations comparing norsar and graefenberg array data and the observed scatter is significantly lower than has been reported for lg data from nevada test site explosions in view of the excellent correspondence found by nuttli 1986 and patton 1988 for lg versus yield at nevada this indicates that rms lg has a potential for yield estimation with very high accuracy at shagan river our study has shown that a selected stations in the ussr and china situated at regional distances provide a much improved signal to noise ratio of the lg phase for events at shagan river as compared to norsar array data b the scaling of rms lg amplitudes between different sized events recorded at the same single station site appears to be consistent with that of norsar indicating a remarkable degree of precision in single station measurements of lg signal c rms lg amplitude measurements for the best of these stations may be made at 1 5 to 2 0 magnitude units lower than at norsar or graefenberg allowing a much lower threshold for lg based yield determination and d the p wave detection capabilities of these single stations do not match those of the noress and arcess arrays thus teleseismic signals continue to be important for detection of small nuclear explosions our conclusion is that lg signals appear to provide an excellent basis for supplying estimates of the yields of nuclear explosions even down to below 1 kt when such signals are recorded at high quality digital in country seismic stations and when calibrated by access to independent nonseismic yield information for a few nuclear explosions at the test sites of interest in the context of monitoring a low yield threshold test ban treaty it will in addition be important to take into consideration various environmental conditions in the testing area such as the possible presence of cavities and to devise appropriate procedures for on site observations in this regard

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

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

strontium isotopic and selected trace element variations between two aleutian volcanic centers adak and atka implications for the development of arc volcanic plumbing systems major and trace element concentrations and initial 87sr 86sr ratios of lavas from the aleutian volcanic centers of adak and atka have been used to study the evolution of their respective lithospheric plumbing systems the centers are within 150 km of one another and show similar overall silica ranges 47 67 but adak 40 km3 is smaller than atka 200 km3 adak s lavas are chemically and isotopically heterogeneous 87sr 86sr 0 70285 0 70330 and two units contain lithospheric xenoliths the lavas of the much larger atka on the other hand have much less variability in major and trace elements as well as 87sr 86sr 0 70320 0 70345 we suggest that these characteristics are a measure of the relative maturity and cleanliness of the lithospheric plumbing systems that supply magma to these centers because aleutian volcanic centers often remain fixed for relatively long periods of time 5 m y once established magmatic passageways are repeatedly used young plumbing systems are relatively cool and contain large amounts of wallrock contaminant and ascending magmas undergo contamination as well as concurrent crystallization and fractionation with time however heat and mass transfer between ascending magmas and wallrock produce thermal and chemical boundary layers that insulate subsequent magmas in effect the plumbing system matures the chemical heterogeneity displayed by young dirty systems like adak reflects not only the magma source but also the wallrock encountered during ascent and possibly the effects of extensive crystal fractionation thus it is the petrologic data of mature clean systems like atka that yield the most direct and unambiguous information on the ultimate origin of the lavas and their near surface evolution

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

experimental determination of ree partition coefficients between amphibole and basaltic to andesitic liquids at high pressure abstract amphibole liquid partition coefficients for the ree damph liqree obtained from natural rocks increase systematically with bulk rock compositional change from basalt to rhyolite and are higher for the middle to heavy ree five new experimentally determined sets of dree la sm eu2 ho lu and 4 published sets are similar to these data and provide values for use in geochemical modelling of magmatic processes involving amphibole over a range of temperature pressure and oxygen fugacity the partition coefficients increase significantly with decreasing temperature and increase slightly with increasing oxygen fugacity pressure does not appear to have a major effect although one data set suggests increased pressure lowers damph liqree in a basaltic composition

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites