the rigid grain net rgn an alternative method for estimating mean kinematic vorticity number wm the use of porphyroclasts rotating in a flowing matrix to estimate mean kinematic vorticity number wm is important for quantifying the relative contributions of pure and simple shear in penetratively deformed rocks the most common methods broadly grouped into those that use tailed and tailless porphyroclasts have been applied to many different tectonic settings however attempts have not been made to unify the various methods here we propose the rigid grain net rgn as an alternative graphical method for estimating wm the rgn contains hyperbolas that are the mathematical equivalents to the hyperbolic net used for the porphyroclast hyperbolic distribution phd method we use the rgn to unify the most commonly used wm plots by comparing the distribution of theoretical and natural tailless porphyroclasts within a flowing matrix test samples from the south tibetan detachment tibet yield indistinguishable results when the rgn is compared with existing methods because of its ease of use ability for comparing natural data sets to theoretical curves potential to standardize future investigations and ability to limit ambiguity in estimating wm the rgn makes an important new contribution that advances the current methods for quantifying flow in shear zones 2006 elsevier ltd all rights reserved

temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

the tolbachik volcanic massif a review of the petrology volcanology and eruption history prior to the 2012 2013 eruption abstract the primary goal of this paper is to summarize all of the published data on the tolbachik volcanic massif in order to provide a clear framework for the geochronologic petrologic geochemical and to a lesser extent the geophysical and tectonic characteristics of the tolbachik system established prior to the 2012 2013 eruption the tolbachik massif forms the southwestern part of the voluminous klyuchevskoy volcanic group in kamchatka the massif includes two large stratovolcanoes ostry sharp tolbachik and plosky flat tolbachik and a 70 km long zone of the basaltic monogenetic cones that form an arcuate rift like structure running across the plosky tolbachik summit the tolbachik massif gained international attention after the 1975 1976 great tolbachik fissure eruption gtfe which was one of the largest eruptions of the 20th century and one of the six largest basaltic fissure eruptions in historical time by the end of the gtfe 2 2 km 3 of volcanic products of variable basaltic compositions with morb like isotopic characteristics covered an area of 1000 km 2 during the following three decades more than 700 papers on various aspects of this eruption have been published both in national and international journals although the recent 2012 2013 eruption which is the main topic of this volume was not as long as the gtfe in duration or as large in area and volume of the erupted deposits it brought to the surface a unique volcanic material never found before in order to understand the data from new eruptions and make significant progress towards a better understanding of the tolbachik magmatic system it is important to be able to put the new results into the historic context of previous research

present day crustal motion along the longitudinal valley fault eastern taiwan abstract the nne striking longitudinal valley fault lvf in eastern taiwan is an extremely active high angle thrust fault it bounds the coastal range and the longitudinal valley which is considered a collision boundary between the philippine sea and the eurasian plates repeated gps data in the longitudinal valley area from 1992 to 1999 are utilized to study the spatial variation of crustal motion along the lvf with respect to penghu in the chinese continental margin velocities for stations on the western side of the lvf longitudinal valley and eastern central range are 18 35 mm yr in directions 283 311 whereas those on the eastern side of the lvf the coastal range are 28 68 mm yr in directions 303 324 a major discontinuity of about 30 mm yr on the rate of crustal motion across the longitudinal valley is attributed to the aseismic slip along the lvf as revealed by trilateration data previously to the south of fengping the block motions of the coastal range are 31 40 mm yr in 317 330 relative to the central range while the near fault motions are 13 33 mm yr in 309 336 various partitions on the left lateral strike slip and convergent components along the lvf are found in the southern longitudinal valley crustal motion is mainly accommodated on the lvf and the luyeh fault in contrast those in the central and northern longitudinal valley are partly taken up on the faults to the east of the lvf or result in the elastic deformation of the coastal range the crustal motion in the northern longitudinal valley area is likely to be distributed in the several ne striking thrusts in a horsetail pattern and obliquely cut the northern coastal range with a small portion of fault slips along the lvf data from dense deployed gps networks across the lvf can be employed to give better estimates of near fault motions and delineate the surface traces of the lvf repeated gps and leveling data from two stations on both ends of the yuli bridge that are 575 m apart clearly indicate that the surface trace of the lvf passes beneath the bridge with oblique horizontal motion of 23 mm yr in 306 and uplift rate of 24 mm yr

seismogenic structure in a tectonic suture zone with new constraints from 2006 mw6 1 taitung earthquake 1 a mw 6 1 earthquake occurred on april 1st 2006 near taitung eastern taiwan it produced significant coseismic ground displacements and a large number of aftershocks in the ensuing month this event provides an opportunity to diagnose the seismogenic structure in the southern longitudinal valley lv of eastern taiwan long viewed as one of the collision sutures between the philippine sea and the eurasian plates with precisely relocated main and aftershock hypocenters focal mechanisms for m 3 8 events and coseismic ground displacements from strong motion records we determine a main shock dislocation model our results indicate that the main shock occurred on a high angle fault azimuth 198 dip 77 the model comprises a fault with two segments the main shock and a large number of aftershocks are associated with the northern segment that exhibited predominantly left lateral strike slip motion in agreement with p wave first motions and waveform usgs solutions the southern segment exhibits a slightly larger thrust component in agreement with cmt solutions tectonically this event highlights a nne trending fault on the west side of the lv which is predominantly strike slip the aftershocks clustered to the east of the main shock which exhibit mainly thrust mechanisms indicate that shortening is still acting on the sedimentary materials deposited between the coastal and central ranges prior to collision as a result the southern lv is undergoing slip partitioning along different faults which has never been specified before

comment on structural analysis of mylonitic rocks in the cougar creek complex oregon idaho using the porphyroclast hyperbolic distribution method and potential use of sc type extensional shear bands as quantitative vorticity indicators

testing the utility of the porphyroclast hyperbolic distribution method of kinematic vorticity analysis kinematic vorticity wk is a dimensionless measure of rotation relative to finite stretching and is essential for complete understanding of flow in ductile shear zones the porphyroclast hyperbolic distribution phd method is a widely used technique for estimating wk based on the acute angle between the flow eigenvectors determined from the orientations of back rotated s porphyroclasts the utility of the phd was tested with tertiary ultramylonites from the santa catalina mountains arizona proterozoic ultramylonites from the virgin mountains nevada and a paleozoic ultramylonite from the hylas zone in the virginia piedmont bootstrapping statistics and a computational sieving process were used to analyze the phd data set average standard deviations of the bootstrapped data sets yield a 1s standard error of 9 for a wk value measured as a simple shear sieving results imply that back rotated porphyroclasts may not orient parallel to the extensional eigenvector the phd method is useful for discerning between deformations that are pure shear dominated general shear or simple shear dominated but is not accurate enough to report precise wk values when performed on multiple sections the phd method can identify zones of monoclinic versus triclinic shear 2007 elsevier ltd all rights reserved

reprint of seismic monitoring of the plosky tolbachik eruption in 2012 2013 kamchatka peninsula russia abstract the active basaltic volcano plosky tolbachik pl tolbachik is located in the southern part of the klyuchevskoy volcano group on the kamchatka peninsula the previous 1975 1976 great tolbachik fissure eruption 1975 1976 gtfe occurred in the southern sector of pl tolbachik it was preceded by powerful earthquakes with local magnitudes between 2 5 and 4 9 and it was successfully predicted with a short term forecast the kamchatka branch of geophysical survey kbgs of the russian academy of science ras began to publish the results of daily seismic monitoring of active kamchatka volcanoes on the internet in 2000 unlike the 1975 1976 gtfe precursor 1 seismicity before the 2012 2013 tolbachik fissure eruption 2012 2013 tfe was relatively weak and earthquake magnitudes did not exceed 2 5 2 precursory earthquake hypocenters at 0 5 km depth were concentrated mainly under the southeastern part of the volcano 3 the frequency of events gradually increased in september 2012 and rose sharply on the eve of the eruption 4 according to seismic data the explosive effusive 2012 2013 tfe began at 05 h 15 min utc on november 27 2012 the outbreak occurred between the summit of the pl tolbachik and the northern breakthrough of the 1975 1976 gtfe 5 because of bad weather early interpretations of the onset time and the character of the eruption were made using seismological data only and were confirmed later by other monitoring methods the eruption finished in early september 2013 this article presents the data obtained through real time seismic monitoring and the results of retrospective analysis with additional comments on the future monitoring of volcanic activity

extracting coherent coda arrivals from cross correlations of long period seismic waves during the mount st helens 2004 eruption 1 we computed cross correlations of seismic waves generated by long period lp events in the frequency band 0 8 2 2 hz the data were recorded in the vicinity of mount st helens msh during an eruptive period from september to december 2004 the time symmetric coherent coda arrivals of the time derivative of the cross correlation function dcf resulting from scattering and topographic effects in msh area correspond to arrivals of the green s function gf between the two stations the dcf waveforms computed on an hourly basis show a remarkable consistency over time periods of several hours but show temporal variations on longer time scales we investigated the emergence rate of the symmetric arrivals of the dcf and discussed their potential applications for volcano monitoring

remote sensing and petrological observations on the 2012 2013 fissure eruption at tolbachik volcano kamchatka implications for reconstruction of the eruption chronology abstract we present a reconstruction of the chronological sequence of events that took place during the first days of the 2012 2013 tolbachik fissure eruption using petrological data and remote sensing methods we were forced to use this approach because bad weather conditions did not allow direct observations during the first two days of the eruption we interpreted infrared images from the scanning radiometer viirs suomi npp and correlated the output with the results of the geochemical study including comparison of the ash deposited at the period from 27 to 29 november with the samples of lava and bombs erupted from the menyailov and naboko vents we argue that the compositional change observed in the eruption products the decrease of sio 2 concentration and k 2 o mgo ratio increase of mgo concentration and mg started approximately 24 h after the eruption began at this time the center of activity moved to the southern part of the fissure where the naboko group of vents was formed therefore this timeframe also characterizes the timing of the naboko vent opening the naboko group of vents remained active until the end of eruption in september 2013

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

postseismic fault healing on the rupture zone of the 1999 m 7 1 hector mine california earthquake we probed the rupture zone of the october 1999 m 7 1 hector mine earthquake using repeated near surface explosions in october 2000 and november 2001 three dense linear seismic arrays were deployed across the north and south lavic lake faults llfs that broke to the surface in the mainshock and across the bullion fault bf that experienced minor slip in that event two explosions each year were detonated in the rupture zone one on the middle and one on the south llf we found that p and s velocities of fault zone rocks increased by 0 7 1 4 and 0 5 1 0 between 2000 and 2001 respectively in contrast the velocities for p and s waves in surrounding rocks increased much less this trend indicates that the hector mine rupture zone has been healing by strengthening after the main shock most likely due to the closure of cracks that opened during the 1999 earth quake the observed fault zone strength recovery is consistent with an apparent crack density decrease of 1 5 within the rupture zone the ratio of travel time decrease for p to s waves was 0 72 consistent with partially fluid filled cracks near the fault zone this restrengthening is similar to that observed after the 1992 m 7 4 landers earthquake which occurred 25 km to the west li and vidale 2001 we also find that the velocity increase with time varies from one fault segment to another at the hector mine rupture zone we see greater changes on the llfs than on the bf and the greatest change is on the middle llf at shallow depth we tentatively conclude that greater damage was inflicted and thus greater healing is observed in regions with larger slip in the mainshock

extensional collapse in the neoproterozoic aracuai orogen eastern brazil a setting for reactivation of asymmetric crenulation cleavage the aracuao orogen of eastern brazil is one of many brasiliano pan african orogens formed during the neoproterozoic assembly of gondwana its western edge bordering the sao francisco craton is the serra do espinhaco fold thrust belt in which top up to the west reverse sense faults west verging folds f1 and east dipping spaced to phyllitic cleavage s1 developed we have found that the kinematics of deformation changes markedly at the hinterland margin of this fold thrust belt here beneath a plateau known as the chapada acaua metadiamictite and fine grained pelitic schist comprise an east dipping belt that contains an assemblage of structures indicative of top down to the east normal sense shear this assemblage includes a cascade of f2 folds that refold f1 folds and verge down the dip of the belt s enveloping surfaces vertical tension gashes and top down to the east rotated clasts based on the presence of these structures we propose that the plateau exposes a regional scale normal sense shear zone here called the chapada acauashear zone casz because f2 folds refold f1 folds normal sense shear in the casz occurred subsequent to initial west verging thrusting considering this timing of motion in the casz we suggest that the zone accommodated displacement of the internal zone of the aracuao orogen down relative to its foreland fold thrust belt and thus played a role in extensional collapse of the orogen the casz trends parallel to preserved thrusts to the west and thus may represent an inverted thrust fault notably throughout the casz s1 schistosity has been overprinted by a pervasive west dipping asymmetric crenulation cleavage s2 the sigmoid shape of s1 surfaces in s2 microlithons require that slip on each s2 surface was top down to the west s2 cleavage is axial planar to the down dip verging f2 folds based on its geometry we suggest that s2 cleavage initiated either as an antithetic extensional crenulation cleavage during reverse sense shear or as a near vertical asymmetric crenulation cleavage formed during east west shortening of a preexisting east dipping schistosity subsequent normal sense shear in the casz reactivated this cleavage causing clockwise rotation of s2 domains as viewed looking along strike to the north in a manner similar to that of rotational bookshelf faults such movement could have accommodated concomitant vertical flattening of the casz during extensional collapse

s coda and rayleigh waves from a decade of repeating earthquakes reveal discordant temporal velocity changes since the 2004 sumatra earthquake temporal changes in the subsurface seismic velocity structure reflect the physical processes that modulate the properties of the media through which seismic waves propagate these processes such a

the eigenvalues of steady flow in mohr space abstract the eigenvalues of the velocity gradients tensor and of the position gradients tensor describing instantaneous flow or incremental deformations are easily determined in mohr space as the points of intersection between a mohr circle and the horizontal mohr axis intersections occur only if the tensor has real eigenvalues eigenvectors associated with the eigenvalues are directions of no rotation a line of material particles under an eigenvector does not rotate during steady flow although the line is instantaneously stretching at a rate equal to its corresponding eigenvalue for non spinning steady sub simple shearing there will always be two eigenvectors the angle between the eigenvectors is dependent on the ratio of pure to simple shearing rates this angle decreases as the pure shearing component decreases relative to the simple shearing component superimposed increments of pure shear and simple shear produce an equivalent set of non rotated material lines but the deformation histories of these lines are rotational the influence of eigendirections on geological structures is constrained by the rheology of a rock during deformation in homogenous steady flow no influence may be obvious spatially periodic material softening along eigenvectors during bulk hardening may result in a complex fabric of intersecting shear zones the geometry of the fabric elements provides important information on the bulk deformation of the rock particularly on the bulk shear sense

kinematic evolution of the mbakop pan african granitoids western cameroon domain an integrated ams and ebsd approach abstract this study integrates anisotropy of magnetic susceptibility microstructural and crystallographic preferred orientation cpo data from the mbakop granitic pluton mgp pan african age in order to decipher its kinematic evolution the mgp lies close to ne sw branch of central cameroon shear zone ccsz and is emplaced in gneissic basement high mean magnetic susceptibility and presence of multi domain magnetite are recorded quartz cpo measured using electron backscatter diffraction reveals dominance of rhomb prism and prism slip in different samples which is consistent with microstructures developed under upper greenschist amphibolite facies conditions quartz cpo along with other kinematic indicators feldspar porphyroclasts mineral fish indicate non coaxial deformation was important during tectonic evolution of the mgp contrasting sense of shear is recorded implying multi stage mylonitization in the western cameroon domain top towards south sense of shear is related to regional d 2 deformation 613 585 ma while top towards north is related to d 3 585 540 ma the magnetic fabric in mgp records d 3 the obliquity between mean orientation of magnetic foliation n12 e and the ne sw ccsz branch n48 e gives kinematic vorticity number of 0 95 this indicates dominantly simple shear with a minor pure shear component it is concluded that regional transpression was important during mgp emplacement

multiple coincident eruptive seismic tremor sources during the 2014 2015 eruption at holuhraun iceland we analyze eruptive tremor during one of the largest effusive eruptions in historical times in iceland 2014 15 holuhraun eruption seismic array recordings are compared with effusion rates deduced from moderate resolution imaging spectroradiometer modis recordings and ground video monitoring data and lead to the identification of three coexisting eruptive tremor sources this contrasts other tremor studies that generally link eruptive tremor to only one source usually associated with the vent the three sources are i a source that is stable in back azimuth and shows bursts with ramp like decrease in amplitude at the beginning of the eruption we link it to a process below the open vents where the bursts correlate with the opening of new vents and temporary increases in the lava fountaining height ii a source moving by a few degrees per month while the tremor amplitude suddenly increases and decreases back azimuth and slowness correlate with the growing margins of the lava flow field whilst contact with a river led to fast increases of the tremor amplitude iii a source moving by up to 25 southwards in 4 days that cannot be related to any observed surface activity and might be linked to intrusions we therefore suggest that eruptive tremor amplitudes energies are used with caution when estimating eruptive volumes effusion rates or the eruption explosivity as multiple sources can coexist during the eruption phase our results suggest that arrays can monitor both the growth of a lava flow field and the activity in the vents

retrieval of moho reflected shear wave arrivals from ambient seismic noise theoretical studies on ambient seismic noise asn predict that complete green s function between seismic stations can be retrieved from cross correlation however only fundamental mode surface waves emerge in most studies involving real data here we show that moho reflected body wave sms and its multiples can be identified with asn for station pairs near their critical distances in the short period band 1 5 s we also show that an uneven distribution of noise sources such as mining activity and wind topography interaction can cause surface wave precursors which mask weaker body wave phases

determining fault geometry from the distribution of coseismic fault slip related to the 2006 taitung earthquake eastern taiwan on 1 april 2006 the taitung earthquake m w 6 1 occurred in taiwan at the boundary between the philippine sea and eurasian plates where high convergence rates contributed to the development of plio pleistocene orogeny in the region from the joint inversion of seismic and geodetic data we identified the event s fault geometry and reconstructed the distribution of coseismic fault slip we modeled fault geometries with increasing complexity and selected the model that best reproduced all datasets simultaneously even though the earthquake magnitude was moderate rupturing occurred in two steps the initial rupture was generated on a listric north south trending fault for which dip decreases with increasing depth and was immediately followed by movement along a perpendicular structure that cross cuts the main fault at 5 km south of the earthquake hypocenter the average slip along the rupture was 30 cm with a maximum of 87 cm oblique reverse fault movement was characterized by a predominant left lateral component the amount of slip is well constrained for offsets of more than 5 cm with an associated uncertainty of 32 for slip amounts greater than 5 cm uncertainties on rake and rupture time are 11 and 0 54 s respectively the rupture propagated from the hypocenter bilaterally moving slightly faster toward the south 2 5 0 4 km s than to the north 1 7 0 1 km s to the south the rupture was rapidly transmitted upward at the junction with the cross cutting east west segment whereas in the north the rupture remained confined to the lower segment of the main fault from global positioning systems gps and seismic data time window 1 min we infer that the cross cutting segment was activated following coseismic rupture on the main north south fault yet close enough in time to be associated with coseismic movement acquired by gps daily solutions

lithospheric structure in northwestern canada from lithoprobe seismic refraction and related studies a synthesis the snorcle refraction wide angle reflection r war experiment snore 97 included four individual lines along the three transect corridors a combination of snore 97 results with those from earlier studies permits generation of a 2000 km long lithospheric velocity model that extends from the archean slave craton to the present pacific basin using this model and coincident near vertical incidence nvi reflection data and geological information an interpreted cross section that exemplifies 4 ga of lithospheric development is generated the velocity structural models correlate well with the reflection sections and provide additional structural compositional and thermal constraints geological structures and some faults are defined in the upper crust at a larger scale the seismic data identify a variety of orogenic styles ranging from thin to thick skinned accretion in the cordillera and crustal scale tectonic wedging associated with both paleoproterozoic and mesozoic collisions models of poisson

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

puzzles and the maximum effective moment mem criterion in structural geology abstract the essential difference in the formation between conjugate brittle shear fractures and ductile shear zones is that the intersection angle of conjugate faults in the contractional quadrants in the former is acute usually 60 and obtuse usually 110 in the latter the mohr coulomb failure criterion is an experimentally validated empirical relationship which structural geologists use to interpret the stress directions based on the orientation of the brittle shear fractures however a simple application of this criterion assuming that the principal stresses are vertical or horizontal throughout the crust fails to explain crustal scale low angle normal faults high angle reverse faults and certain types of conjugate strike slip faults that have intersection angles in the compressional quadrants greater than 90 although the maximum effective moment mem criterion has been used to analyze structures in several natural cases and obtained some new evidence in nature and experiments it is not yet commonly used to interpret non mohr coulomb features widely distributed in the crust it is important to review the mem criterion and its implications for explaining the formation mechanism of naturally occurring faults and shear zones behavior of a rock depends on its mechanical properties the latter in turn depends on pressure and temperature conditions related to crustal depth and strain rates conjugate fractures with obtuse angles ca 110 in the contractional direction at different scales and at different crustal levels are consistent with the prediction of the mem criterion and suggest deformation at low strain rates thus strain rate clearly plays an important role in the style of crustal deformation and the many observed departures from the mohr coulomb failure criterion

brittle shear zones in experimentally deformed quartz single crystals abstract intracrystalline shear zones developed in a quartz single crystal that was experimentally deformed to 26 finite strain under conditions favourable for macroscopically ductile deformation the crystal was uniaxially compressed parallel to c in the presence of 1 vol of added water at a temperature of 800 c a confining pressure of 1200 mpa and a strain rate of 10 6 s 1 we investigated how the shear zones initiated and how their structure evolved with ongoing deformation detailed crystallographic orientation analyses were carried out with the help of the electron backscatter diffraction ebsd technique and complemented by transmission electron microscopy tem the shear zones appeared to develop along planar microcracks oriented parallel to crystallographic rhomb planes further microcracking resulted in cataclastic shear zone development new grains developed by rotation of fracture fragments the rotation of the fragments in the shear direction was probably facilitated by the high water pressure and the relatively high porosity in the shear zone shear zones finally exhibit a strong crystallographic preferred orientation cpo our results suggest that cataclastic deformation processes may lead to shear zone development the cpo developed within the shear zones through dynamic recrystallisation i e new grains with c oriented approximately perpendicular to the shear zone boundary grew at the cost of other new grains

the initiation and evolution of the transpressional straight river shear zone central fiordland new zealand abstract structural data and u pb geochronology on zircon from central fiordland new zealand show the role of pre existing structural heterogeneities in the kinematic evolution of a newly discovered zone of transpression the straight river shear zone consists of steep zones of high strain that are superimposed onto older fabrics across a 10 80 km region the older foliation formed during two periods of tectonism contraction and magmatism of mostly carboniferous 312 306 ma age and early cretaceous batholith emplacement ending by 113 4 1 7 ma followed by extension that ceased by 88 4 1 2 ma the primary mechanism for the formation of steep shear zone foliations was the folding of these older fabrics conjugate crenulation cleavages associated with the folding record shortening at high angles to the shear zone boundaries fold axial surfaces and axial planar cleavages strike parallel to the shear zone with increasing strain as they progressively steepened to subvertical in most areas shear sense flips from oblique sinistral east side down component to oblique dextral west side down across zones of intermediate and high strain high strain zones display subvertical mineral lineations steep strike slip faults and shear sense indicators that record strike slip motion across the steep lineations these patterns reflect triclinic transpression characterized by narrow zones of mostly strike slip deformation and wide zones of mostly contraction zones of high strain align with offshore traces of late tertiary strike slip faults suggesting that a previously undocumented component of late tertiary shortening and strike slip motion is accommodated within fiordland

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

tandem x time series analysis reveals lava flow volume and effusion rates of the 2012 2013 tolbachik kamchatka fissure eruption assessing eruption volumes is one of the major challenges in volcano research but provides valuable insights into the dynamics of an eruption and the associated hazard one way to estimate this important parameter is the generation and differencing of digital elevation models dems acquired before during and after an eruption the satellite mission tandem x enables generation of time series of dems using synthetic aperture radar satellite imagery we use these data to study the 2012 2013 eruption of tolbachik in kamchatka we developed a processing scheme for generation of 18 dems from tandem x imagery that relies on the generation of a preeruption dem which is used to process the syneruption and posteruption data pairs differencing each dem with the preeruption dem enables mapping the lava flows and measuring lava flow volume over time and to estimate lava extrusion rates we find a final lava flow volume of 0 53 km3 covering an area of 36 km2 by the end of the eruption an uncertainty analysis is performed while analyzing the dem differences in areas where no topographic change is expected leading to an error of 0 01 km3 for the final lava flow volume the lava effusion was with 247 92 m3 s very high in the first days of the eruption and rapidly decayed toward its end while many basaltic eruptions follow an exponentially decaying flow model the extrusion rates at tolbachik are more compatible with a 1 t model this special characteristic might be useful to gain further insight into the eruption process at tolbachik

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

temporal changes of surface wave velocity associated with major sumatra earthquakes from ambient noise correlation abstract detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis here we report temporal changes of surface wave velocity over a large area associated with 3 major sumatra earthquakes in 2004 2005 and 2007 we use ambient noise correlation to retrieve empirical green s function egf of surface waves between stations because the process is completely repeatable the technique is powerful in detecting possible temporal change of medium we find that 1 excellent station pair psi in indonesia and chto in thailand shows significant time shifts up to 1 44 s after the 2004 and 2005 events in the rayleigh waves at 10 20 s but not in the love waves suggesting that the rayleigh time shifts are not from clock error the time shifts are frequency dependent with the largest shifts at the period band of 11 16 s we also observe an unusual excursion 1 month before the 2004 event we obtain a total of 17 pairs for june 2007 to june 2008 which allow us to examine the temporal and spatial variation of the time shifts we observed strong anomalies up to 0 68 s near the epicenter after the 2007 event but not in the region further away from the source or before the event or 3 months after the event the observations are interpreted as stress changes and subsequent relaxation in upper mid crust in the immediate vicinity of the rupture and the broad area near the fault zone

timing and processes of late mesozoic mid lower crustal extension in continental ne asia and implications for the tectonic setting of the destruction of the north china craton mainly constrained by zircon u pb ages from metamorphic core complexes abstract late mesozoic large scale crustal extension occurred across the northeastern section of continental asia and metamorphic core complexes mccs are the major features in this region this paper presents new zircon u pb and ar ar ages of biotite and hornblende for pre or syn mylonitized and post kinematic unmylonitized intrusions from these mccs and attempts to determine the timing of initiation duration and termination of the mid lower crustal ductile extension by integrating with geochronological data from previous studies these mccs have similar 40 ar 39 ar biotite and hornblende ages 130 to 110 ma mainly from 130 to 120 ma which are interpreted as the cooling ages and represent the timing of the late stage formation of the mccs zircon u pb ages for syn to post kinematic intrusions from some mccs suggest that the mid lower crustal extension probably initiated at ca 150 145 ma with a peak occurring 145 130 ma and continued to 130 120 ma which is older than that suggested by 40 ar 39 ar ages by 10 20 ma the early ductile extension most likely initiated in mongolia and northern china during the late jurassic 150 145 ma at a deeper level then propagated southwards 140 130 ma and finally developed throughout the entire continental ne asia 130 120 ma based on the timing and processes of the extension a geodynamic model and tectonic setting of the destruction of the north china craton ncc are proposed

distribution of seismic wave speed changes associated with the 12 may 2008 mw 7 9 wenchuan earthquake 1 we used continuous recordings in sichuan china to track the temporal change of the seismic wave speed at a regional scale for 2 years including the wenchuan mw 7 9 earthquake the data are recorded by a temporary network of 156 broad band seismographs in a region that covers the southern 2 3 of the fault activated during the earthquake a doublet analysis applied on the codas of seismic noise cross correlation functions is used to detect temporal velocity changes we found clear evidence that the seismic velocity drops by up to 0 08 in the fault region just after the earthquake with fluctuations within 0 02 before the earthquake we compared the measurements in different sub arrays to get a spatial distribution of the velocity changes this distribution is consistent with the volumetric strain change during the wenchuan earthquake and shows that the co seismic velocity change is not controlled by the response of sediments

body wave imaging of earth s mantle discontinuities from ambient seismic noise ambient seismic noise correlations are widely used for high resolution surface wave imaging of earth s lithosphere similar observations of the seismic body waves that propagate through the interior of earth would provide a window into the deep earth we report the observation of the mantle transition zone through noise correlations of p waves as they are reflected by the discontinuities associated with the top 410 kliometers km and the bottom 660 km of this zone our data demonstrate that high resolution mapping of the mantle transition zone is possible without using earthquake sources

kinematic analysis using ams data from a deformed granitoid abstract this study highlights the usefulness of anisotropy of magnetic susceptibility data from a deformed granitoid in deciphering its kinematic evolution vis a vis shear zone data are presented from the chakradharpur granitoid ckpg that lies to the north of the northerly dipping ene wsw striking singhbhum shear zone ssz eastern india whilst the foliation recorded in the field in some parts of the granitoid is parallel to the ssz the magnetic foliation is n54 e 90 mean orientation it is suggested that the magnetic fabric provides a window into an evolutionary stage prior to the final shearing thrusting event the evidence of which is preserved on the mesoscopic scale it is envisaged that during the initial stages of deformation there was simple shear along the evolving ssz that resulted in sinistral strike slip movement the vorticity axis at this stage was steeply plunging and sense of rotation was anticlockwise space was generated in a direction n25 e perpendicular to maximum instantaneous stretching axis into which ckpg emplaced synchronously with regional deformation and evolving ssz with continued deformation there was thrusting along the ssz the vorticity axis flipped to a sub horizontal orientation thus leading to the development of down dip stretching lineations and sheath folds within the ssz however at the same time the vorticity axis responsible for fabric evolution within the syntectonically crystallizing cooling ckpg was steeply plunging with clockwise rotation the magnetic foliation mean orientation n54 e 90 developed during the final stage of syntectonic crystallization however deformation in the region and thrusting along the ssz continued even after the ckpg had fully crystallized and solidified which led to the development of the ene wsw striking mesoscopic foliation that is parallel with the ssz we propose that the angle between the magnetic foliation and the ssz foliation recorded in the field enables to decipher the kinematic vorticity number of flow responsible for fabric evolution of the ckpg it is concluded that transpression was an important mechanism and during regional deformation whilst the ssz developed structures by dominantly simple shear the ckpg underwent dominantly pure shear

temporal changes of seismic velocity associated with the 2006 mw 6 1 taitung earthquake in an arc continent collision suture zone 1 to detect temporal changes of elastic properties associated with the 2006 mw 6 1 taitung earthquake in southeast taiwan whereby the collision between the luzon arc riding on the philippine sea plate and the asian margin is taking place we construct the green s functions from auto and cross correlation function acf and ccf of continuous ambient noise between stations time lapse changes in the retrieved coda arrivals are estimated for monitoring spatiotemporal variations of seismic velocities around the ruptured fault zones to the south of the main shock epicenter where the earthquake may have ruptured along two perpendicularly intersecting fault planes resulting in intense coseismic slip and widely dispersed aftershocks the acfs 2 8 hz at nearby stations reveal a large sudden velocity drop of over 1 after the event occurrence the ccfs 0 1 0 9 hz also show moderate reduction about 0 1 for the interstation paths traveling through the southeast quadrant of the focal sphere which has experienced the maximum peak ground acceleration and dilatational strain change the intense seismic shaking combined with the rupture induced damage near the junction of the two faults is the most plausible cause for such localized but significant coseismic velocity reduction the response of groundwater levels to precipitation is in phase correlated with velocity variations over 3 years of investigation unlike the postseismic surface displacements gradually relaxed the velocity remained slow until october 2006 due to the typhoon induced heavy rains between may and september

lithospheric structure beneath the archaean slave province and proterozoic wopmay orogen northwestern canada from a lithoprobe refraction wide angle reflection survey the slave geological province a relatively small craton in nw canada that includes the oldest rocks in the world is one of five cratons that form the archaean continental core of north america the palaeoproterozoic wopmay orogen lying between the craton and the phanerozoic northern canadian cordillera represents crustal growth through addition of a series of north south oriented magmatic arcs and accreted terranes as part of lithoprobe s multidisciplinary studies line 11 of the snore 97 seismic refraction wide angle reflection survey investigated the structure of the lithosphere in this region interpretation of crustal and mantle arrivals from 13 record sections followed an iterative procedure of traveltime inversion and forward modelling results show that crustal thickness at 32 35 km remains relatively constant from the archaean regions in the east to proterozoic domains in the west contrary to average values of crustal thicknesses from global compilations that suggest thicker proterozoic crust at the westernmost end of the line where crustal extension and basin formation are inferred the crust thins to 30 km upper crustal velocities to about 12 km depth lie in the range of 5 8 6 2 km s 1 the middle crust of thickness 8 10 km has velocities between 6 2 and 6 6 km s 1 average velocities for the lower crust differentiated as a 10 km thick layer range between 6 6 and 6 9 km s 1 with a higher velocity region 7 1 km s 1 in the transition zone between the fort simpson magmatic arc and hottah accreted terrane in the wopmay orogen where a palaeoproterozoic subduction zone has been inferred from coincident multichannel reflection data in the same area anomalously low upper mantle velocities 7 5 km s 1 have been found indicating that the effects of collision subduction and accompanying physical changes in the rocks comprising the mantle lithospheric wedge above the underthrusting structure may have been retained for 1800 ma data from most record sections with offset distances greater than 250 km show continuous wide angle reflections from upper mantle depths of about 75 km and almost 100 km although poorly constrained velocities in this depth range vary from 8 4 to 8 8 km s 1 interpretation of these phases and mantle reflections from equivalent depths in coincident near vertical incidence multichannel data relates them to subduction and underthrusting of oceanic crust and subsequent phase changes that occurred during the assembly of the craton and the evolution of the palaeoproterozoic orogen

plate boundary strain partitioning along the sinistral collision suture of the philippine and eurasian plates analysis of geodetic data and geological observation in southeastern taiwan crustal deformation and strain partitioning of oblique convergence between the philippine sea plate and the eurasian plate in the southern longitudinal valley of eastern taiwan were characterized based on geodetic analysis of trilateration network and geological field investigation the longitudinal valley fault one of the most active faults on taiwan branches into two individual faults in the southern longitudinal valley these two active faults bound the plio pleistocene pinanshan conglomerate massif between the coastal range the luzon island arc belonging to the philippine sea plate and the central range the metamorphic basement of the eurasian plate a geodetic trilateration network near the southern end of the valley shows a stable rate of the annual length changes during 1983 1990 the strain tensors for polygonal regions including triangular regions of the taitung trilateration network reveal that there are two distinct zones of deformation a zone of shortening thrusting between the pinanshan massif and the central range on the west and a strike slip movement between the pinanshan massif and the coastal range on the east the analysis of a discontinuity model consisting of three rigid blocks separated by two discontinuities has been carried out the results show that the deformation in this region can be characterized by two major faults a reverse fault is located between the plio pleistocene pinanshan massif and the metamorphic basement of the central range with a shortening rate of about 12 mm yr in the direction n280 e a strike slip fault is located principally along the river between the pinanshan massif and island arc system of the coastal range with a purely strike slip component of about 22 mm yr in the direction n353 e the analysis of the geodetic data further suggests that substantial deformation probably strike slip in type occurs within the pinanshan massif geological evidence of deformation in the plio pliestocene pinanshan conglomerate includes regional folding a conjugate set of strike slip fractures at the outcrop scale and morphological lineaments related to fracturing all indicating that the pinanshan massif is being deformed within a transpressive stress regime regional kinematic data indicate that a significant portion of the 82 mm yr of motion between the eurasian plate and the philippine sea plate is absorbed in the southern longitudinal valley by the decoupling of two distinct major faults the geometry of the oblique convergence and the rheology of the rock units the well consolidated plio pleistocene conglomerate and the sheared melange formation play the two important roles in the partitioning of crust deformation

green s functions extraction and surface wave tomography from microseisms in southern california we use crosscorrelations of seismic noise data from 151 stations in southern california to extract the group velocities of surface waves between the station pairs for the purpose of determining the surface wave velocity structure we developed an automated procedure for estimating the green s functions and subsequent tomographic inversion from the 11 325 station pairs based on the characteristics of the noise field we eliminate specific events by a procedure that does not introduce any spurious spectral distortion in the band of interest 0 05 0 2 hz further we only used the emerging arrival structure above a threshold signal to noise ratio the result is that mostly station pairs with their axes oriented toward the sea are used consistent with the noise having a microseism origin finally it is the time derivative of the correlation function that is actually related to the green s function the emergence of the time domain green s function is proportional to the square root of the recording time and inversely proportional to the square root of the distance between stations the tomographic inversion yields a surface wave velocity map that compares favorably with more conventional and elaborate experimental procedures

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

crustal and mantle shear velocity structure of costa rica and nicaragua from ambient noise and teleseismic rayleigh wave tomography the costa rica nicaragua subduction zone shows systematic along strike variation in arc chemistry geology tectonics and seismic velocity and attenuation presenting global extremes within a few hundred kilometres in this study we use teleseismic and ambient noise derived surface wave tomography to produce a 3 d shear velocity model of the region we use the 48 stations of the tucan array and up to 94 events for the teleseismic rayleigh wave inversion and 18 months of continuous data for cross correlation to estimate green s functions from ambient noise in the shallow crust 0 15 km we observe low shear velocities directly beneath the arc volcanoes 40 km thick crust beneath the costa rican arc and the nicaraguan highlands thinned crust 20 km beneath the nicaraguan depression and increasing crustal thickness in the backarc region consistent with receiver function studies the region of thinned seismically slow and likely weakened crust beneath the arc in nicaragua is not localizing deformation associated with oblique subduction at mantle depths 55 120 km depth we observe lower shear velocities up to 3 per cent beneath the nicaraguan arc and backarc than beneath costa rica our low shear velocity anomaly beneath nicaragua is in the same location as a low shear velocity anomaly and displaced towards the backarc from the high vp vs anomaly observed in body wave tomography the lower shear velocity beneath nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature finally we observe a linear high velocity region at depths 120 km parallel to the trench which is consistent with the subducting slab

sudden drop of seismic velocity after the 2004 mw 6 6 mid niigata earthquake japan observed with passive image interferometry 1 passive image interferometry pii is a seismological method employing ambient seismic noise to monitor the temporal evolution of mean shear wave velocity within the earth first the elastic green s tensor between two seismometers is computed from the cross correlation of seismic noise recorded during a certain period second the constructed seismograms of different time periods are treated as earthquake multiplets and small time shifts in their coda are used to invert a relative change in mean shear wave velocity when applied to the source region of the 2004 mw 6 6 mid niigata earthquake japan centroid depth 5 km we used noise recorded at six seismometers located at a distance of less than 25 km from the epicenter daily inversions during the 2 months before and after the earthquake show a sudden drop of mean shear wave velocity of some tenths of a percent at the time of the mid niigata earthquake using noise in two frequency bands 0 1 0 5 hz and 2 8 hz we find similar amplitudes for the velocity drop which indicates that changes are not restricted to the shallow subsurface possible interpretations of this velocity decrease are a decrease of crustal stress after the earthquake a nonlinear site response in the shallow subsurface layer due to strong ground motion or structural weakening due to the creation of new fractures in the source area of the earthquake

traveltime measurements from noise correlation stability and detection of instrumental time shifts we test the feasibility of using green s functions extracted from records of ambient seismic noise to monitor temporal changes in the earth crust properties by repeated measurements at regional distances we use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in california the correlations are computed in a moving 1 month window and we analyse the temporal evolution of measured interstation traveltimes the comparison of the arrival times in the positive and negative correlation time of rayleigh and love waves allows us to separate time shifts associated with any form of physical change in the medium those resulting from clock drift or other instrumental errors and those due to change in the localization of the noise sources this separation is based on the principle of time symmetry when possible we perform our analysis in two different period bands 5 10 and 10 20 s the results indicate that significant instrumental time errors 0 5 s are present in the data these time shifts can be measured and tested by closure relation and finally corrected independently of any velocity model the traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise between 1999 and 2005 the final arrival time fluctuations have a variance of the order of 0 01 s this allows us to measure interstation traveltimes with errors smaller than 0 3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period this level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in california such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes

temporal velocity changes in the crust associated with the great sumatra earthquakes abstract co and postseismic slip of the great earthquakes can give rise to temporal changes in the medium either due to strong ground motion damaging near surface sediment layer or stress perturbations modulating crack density and or fluid movement at depth such time varying crustal properties can result in fractional change in seismic velocity that can be probed from cross correlating waveforms and measuring their time lags within a repeating earthquake sequence this study analyzes lag times of high frequency 0 5 2 0 hz p and s coda waves as well as long period 0 03 0 1 hz surface waves from repeating aftershock sequences of the great 2004 sumatra andaman and 2005 nias simeulue earthquakes the observed lag times reveal several major characteristics 1 lag time series t of s coda for the 2004 sequences fluctuate around zero and are sometimes negative as a function of lapse time whereas t of s coda for the 2005 sequences exhibit a monotonic increase as a function of lapse time 2 average velocity reduction of s coda v s is about two times larger than that of p coda v p average velocity reduction of rayleigh waves v lr is 3 4 times larger than that of love waves v lq and 3 v s and v lr display temporal velocity recovery with calendar time especially for the 2005 sequences the form of temporal velocity recovery of v s of the 2005 sequences is similar to available displacement time series of the nearby geodetic station whereas we discuss potential artifacts such as source separation temporal changes of the noise field and instrument response observations collectively point to nonuniform temporal velocity reduction in the crust modulated by co or and postseismic slip of the 2004 2005 great earthquakes online material table of source parameters and figure showing tests on lag time measurements of long period rayleigh waves

maximum effective moment criterion and the origin of low angle normal faults abstract the origin of the low angle normal faults of metamorphic core complexes has been debated for over two decades proponents of andersonian fault mechanics have long argued that it is mechanically unfeasible for slip to occur along shallowly dipping normal faults a new theory named the maximum effective moment criterion is proposed here for their origin using an effective moment approach formulated as m eff fh where f is the force tangentially acting on the unit shear boundaries and h represents its arm the maximum value appears at angles of 54 7 with the 1 since extensional crenulation cleavages eccs and the contractional crenulation cleavages cccs occur in conjugate pairs with 110 angle between them it is suggested that they tend to be oriented in the directions of maximum effective moment the differential stress for formation of the ecc or ccc are less than that for fracturing the orientations of conjugate eccs depending on relative magnitudes of simple shear versus coaxial strain components the synthetic ecc set is much better developed than the antithetic set due to anisotropy upward propagation of the synthetic ecc set from mid crustal domains of mylonitization through strain localization and strain softening is considered an effective mechanism for the formation of the low angle normal faults of metamorphic core complexes

diapiric exhumation of earth s youngest uhp eclogites in the gneiss domes of the d entrecasteaux islands papua new guinea abstract the woodlark rift in papua new guinea hosts the world s youngest 2 8 ma eclogite facies rocks and extensional deformation has played a key role in exhuming these u hp rocks at rates of 20 mm yr during the eocene papuan arc continent collision australian plate derived continental rocks were subducted to u hp depths there they remained for up to 30 m y until the pliocene when asthenospheric circulation ahead of the west propagating woodlark spreading ridge introduced heat and fluids this caused rocks to break away from the paleosubduction channel recrystallize in the eclogite facies and rise as rayleigh taylor instabilities the diapirs ascended adiabatically undergoing partial melting which lowered their viscosity and increased buoyancy u hp crust ponded near the moho at 2 4 ma thickening the crust to 40 km 11 kb domal uplifts emerged above sea level and these are still underlain by an unusually thick crust 26 km for a rift that has stretched by factor of 3 since 6 ma after ponding they acquired a flat lying foliation during amphibolite facies retrogression vertical shortening accompanied the gravitationally driven outflow of ponded lower crust the weak material was extended parallel to the rift margin thinning ductilely by w k 0 2 and was mechanically decoupled from and orthogonal to plate motion in the rift top e shear fabrics suggest that this flow was westward perhaps driven by isostatic stresses towards a strongly thinned rift corridor ahead of the woodlark spreading ridge at 100 c per m y and were mechanically incorporated into the rift s upper crust final exposure was by normal faulting and minor erosion such exhumation may also apply to other u hp terranes where less evidence for moho ponding is preserved

reconstructing green s function by correlation of the coda of the correlation c3 of ambient seismic noise analysis of long range correlation of the microseisms has been shown to provide reliable measurements of surface wave speeds that can be used for seismic imaging and monitoring in the case of an even distribution of noise sources it has been theoretically demonstrated that the correlation is the exact green s function including all types of waves this method is limited in its application by the actual source distribution in practice the azimuthal distribution of energy flux of the noise is dominated by some particular directions resulting in a clear azimuthal dependence of the quality of the reconstruction of rayleigh waves with a poor reconstruction in some azimuths to solve this problem we use noise correlations measured on the entire network we consider two stations a and b for which the rayleigh waves could not be discerned in the in the correlation of continuous records of ambient noise we computed all correlations between the station a respectively b and all the 150 other stations located at regional distances theoretically these virtual seismograms contain direct waves and coda although they are clearly contaminated by the influence of the imperfect ambient noise field and most are inadequate for direct analysis we used these correlation functions as equivalents to seismograms produced by sources acting at the 150 stations locations and recorded in a respectively b we select time windows in those virtual seismograms that correspond to coda and compute correlations between them this metacorrelation is found to exhibit the surface wave part of the green s function that was not visible in the raw correlation of ambient noise we illustrate the legitimacy of the reconstruction by comparison with raw noise correlations this procedure can be used to assess seismic velocity between stations even in presence of a directive and poorly oriented ambient noise the result shows that in spite of the small signal to noise ratios often seen in correlations of ambient noise especially at large lag time corresponding to coda their codas are better equipartitioned than was the ambient noise upon which they were based they are therefore presumably multiply scattered and contain information on both direct surface waves and also on more complex travel paths

large amplitude moho reflections sms from landers aftershocks southern california closely spaced aftershocks of the 28 june 1992 landers earthquake m w 7 3 were used to make event record sections that show the transverse components of s and sms arrivals at a distance of 70 to 170 km for the data recorded toward the north in the mojave desert large sms phases are observed with amplitudes 2 to 5 times greater than the direct s for similar distances to the south the sms arrival is comparable to or smaller than the s comparisons to synthetic seismograms indicate that the large amplitude sms phases are produced by the simple crustal structure of the mojave desert that allows a large moho reflection in contrast the more complex geologic structure to the south partitions the seismic energy into a more complicated set of seismic phases so that the moho reflection is diminished in amplitude the large sms phases observed in the mojave enhance the overall ground motions by a factor of 2 to 3 this suggests that when damaging earthquakes occur in other regions of simple crustal structures moho reflections will produce amplified strong motions at distance ranges around 100 km depending on the local structure

temporal changes of medium properties during explosive volcanic eruption volcanic evolutions typically accompany significant changes in medium properties monitoring the seismic properties may be useful in identifying the state of volcanic evolution temporal variation of shallow crustal vp vs ratios before and during the 2009 eruption of redoubt volcano alaska is investigated using the p and s traveltimes of local earthquakes high vp vs ratios of 1 9 are observed over a wide region in the precursory phase suggesting the presence of partial melts in the medium at least several months before explosive eruptions the high v p v s ratios decrease until the early effusive phase with rates of 0 179 year 1 in the precursory phase 65 days and 2 147 year 1 in the explosive phase 40 days which is equivalent to a decrease in the bulk modulus of fluids by 1 1 and 7 9 gpa respectively the decreasing v p v s ratios in the precursory phase may be due to increasing amounts of overpressurized gas and water vapor in the medium the rapid decrease in vp vs ratios during the explosive phase may be caused by melt eruption and gas emission the vp vs ratios were observed to be nearly stationary since the early effusive phase suggesting rare presence of melts and low levels of pore pressures with degassing these observations suggest that monitoring vp vs ratios may be useful to identify the eruption state

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

taylor mill analogues for patterns of flow and deformation in rocks abstract the giesekus design of taylor s four roll mill has been restored and is here used in novel flow visualizations of both pulsating and monotonously increasing strains the particle movement paths and progressive deformation patterns visualized in these physical experiments are in agreement with those previously calculated analytically and constructed graphically the progressive deformation of passive material markers is guided by flowlines circular flowlines accommodate rigid body rotations without deformation elliptical flowlines result in pulsating strains the maximum strain occurs when material particles which were initially at the short axis of the elliptical flowlines reach the long axis of the flow patterns monotonically increasing strains occur when flowlines are hyperbolic the insight thus gained is extrapolated to suggest practical methods and assumptions that allow the reconstruction of particle movement paths from deformation features commonly observed in rocks

oblique lineations in orthogneisses and supracrustal rocks vertical partitioning of strain in a hot crust eastern borborema province ne brazil detailed structural work conducted at the eastern area of the neoproterozoic brasiliano zpan african borborema province northeastern brazil has shown two orientations of stretching lineations with ese trend in supracrustal rocks and ne trend in underlying orthogneisses in the metasedimentary sequence numerous kinematic indicators showing a top to the northwest sense of shear denote a welldeveloped non coaxial deformation in the orthogneisses lineations formed dominantly during coaxial deformation although a component of ne directed shear is locally observed the two lineations were produced under similar high temperature metamorphic conditions and are interpreted as the result of a protracted nw se contractional strain regime where i subhorizontal non coaxial shear with superimposed flattening led to an initial phase of nw directed thrusting ii flattening strains mainly accumulated in the orthogneisses with progressive deformation leading to a lineation oblique to the transport direction iii the subhorizontal fabric in basement and cover rocks was refolded by overturned folds and then iv cross cut by conjugate ene striking dextral and nne striking sinistral shear zones contemporaneous with ne trending upright folds it is proposed that vertical partitioning of strain between basement and cover may explain the presence of oblique lineations in this orogenic belt that did not go through a final stage of extensional collapse q 2005 elsevier ltd all rights reserved

structural analysis of mylonitic rocks in the cougar creek complex oregon idaho using the porphyroclast hyperbolic distribution method and potential use of sc type extensional shear bands as quantitative vorticity indicators abstract mylonitic rocks of the cougar creek complex of northeastern oregon and west central idaho provide an opportunity to document the deformational structures produced during general non coaxial shear within quartz feldspar mylonites and to explore the potential role of sc type extensional shear bands in vorticity analysis well developed feldspar porphyroclasts within six mylonite zones were utilized to estimate bulk kinematic vorticity w k using the porphyroclast hyperbolic distribution phd method w k values for the cougar creek mylonites range from w k 0 26 to w k 0 37 synthetic and antithetic shear band inclinations were measured relative to observed shear zone boundaries within five mylonite zones with estimated w k values and compared to the non coaxial flow field geometries and eigenvector orientations in each mylonite zone synthetic sc type shear band populations exhibit a range of inclination with maximum inclination lying approximately parallel to the acute bisector ab of the eigenvectors similarly antithetic shear band populations show a range of inclination near the obtuse bisector ob of the eigenvectors we infer that sc type extensional shear bands form initially parallel to ab and ob and rotate towards the flow plane with progressive deformation decreasing their inclination relative to the shear zone boundary ab and ob have significance in the strain field in that they represent orientations of maximum angular strain rate thus planes perpendicular to ab and ob are mechanically favorable for small zones of localized simple shear shear bands within the heterogeneous bulk strain of the mylonite orientation analysis of populations of sc type shear bands may provide a direct quantitative means of estimating w k

emissions of trace elements during the 2012 2013 effusive eruption of tolbachik volcano kamchatka enrichment factors partition coefficients and aerosol contribution abstract gases and aerosols from the 2012 13 effusive eruption of tolbachik basaltic volcano kamchatka were sampled in february and may 2013 from a lava tube window located 300 m from the eruptive crater temperature at the sampling point was 1060 1070 c the chemical and isotopic compositions of the sampled gases 92 4 h 2 o 3 5 co 2 2 3 so 2 on average d from 25 0 to 38 6 correspond to a typical volcanic arc gas without dilution by meteoric or hydrothermal water halogen contents in the gases 1 37 hcl 0 5 hf were higher than average arc values the total amount of analyzed metallic and metalloid trace elements in the gas exceeded 665 ppm six most abundant trace elements k 250 ppm na 220 ppm si 74 ppm br 48 ppm cu 21 ppm and fe 12 ppm accounted for 95 of the total content of trace elements in the gas the gases contained 24 ppb re 12 ppb ag 4 9 ppb au and 0 45 ppb pt refractory rock forming elements mg al ca and some other elements such as ba and th were transported mainly in the form of silicate microspheres and altered rock particles the concentrations of metals in the eruptive tolbachik gases are higher than the corresponding concentrations in high temperature fumaroles worldwide although the mutual ratios of the elements are approximately the same the gas magma partition coefficients of eleven elements exceed unity including the non metals f s cl br as se and te and the rare metals cd re tl and bi despite the relatively low concentrations of trace elements in the volcanic gases at the highest temperatures superficial magma degassing provides information on the sources and sinks of metals

monitoring of the volcanic rock compositions during the 2012 2013 fissure eruption at tolbachik volcano kamchatka abstract here we present the results from monitoring of the composition of rocks produced during the 2012 2013 fissure eruption at tolbachik volcano fte major and trace element concentrations in 75 samples are reported products of this eruption are represented by high alumina basaltic trachyandesites with higher alkalis and titanium contents than in all previously studied rocks of the tolbachik monogenetic volcanic field rocks erupted during the first three days 27 30 november from the northern also called menyailov group of vents are the most silica and alkali rich sio2 concentrations up to 55 35 wt and k2o up to 2 67 wt from december onwards when the eruptive activity switched from the menyailov vents to the southern naboko group of vents silica content dropped by 2 wt concentrations of mgo feo tio2 and mg increased and k2o and na2o concentrations and k2o mgo ratio decreased for the rest of the eruption the compositions of rocks remained constant and homogeneous no systematic compositional differences between lava bombs and scoria samples are evident trace element distributions in the rocks of the menyailov and naboko vent lavas are relatively uniform menyailov lavas have slightly higher th nb hf y and hree concentrations than the naboko vent lavas at more or less constant element ratios we explain the initial change in geochemistry by tapping of a slightly cooler and fractionated 3 mt and 8 cpx upper part of the magma storage zone before the main storage area began to feed the eruption thermodynamic constraints show that apparent liquidus temperatures varied from 1142 c to 1151 c and thermodynamic modeling shows that variations in compositions are consistent with a high degree of low pressure 100 300 mpa nominally anhydrous fractionation of a parent melt compositionally similar to the 1975 northern breakthrough high mg basalt geochemistry petrological observations and modeling are in agreement with the newly erupted material being derived from remnant high al magma from the 1975 76 southern breakthrough eruption with only slight amounts of cooling less than 1 c per year during the intervening 36 years

efficiency of lg propagation from sms dynamic ray tracing in three dimensionally varying crustal waveguides the effects of variations in crustal and basin thicknesses on the efficiency of lg propagation in central asia are investigated by comparing the predictions of ray theoretical modeling of lg as multiple critically reflected sms rays with observations at the knet cnet and ilpa arrays ray modeling predicts that strong spatial gradients in crustal thickness within 10 to 50 km of either the source or receiver can affect lg efficiency over paths exceeding 500 km variations in the efficiency of lg propagation to knet including instances of strong variations across the aperture of the array are consistent with predicted blockage of sms by high slopes of moho topography associated with the hindu kush and pamir mountains at cnet and ilpa the blocking effects of moho slopes associated with the caucausus and zagros mountain belts and black and caspian seas are accentuated by the effects of thick basins thick basins greater than 2000 m are found to have large effects on the efficiency of lg propagation from shallow 1 km crustal sources blocking either a portion or all of the lg phase along paths crossing these basins the basin effects are strongly sensitive to source depth nearly vanishing for sources 15 km and deeper

deep and shallow long period volcanic seismicity linked by fluid pressure transfer volcanic long period earthquakes are attributed to pressure fluctuations that result from unsteady mass transport in the plumbing system of volcanoes whereas most of the long period seismicity is located close to the surface the volcanic deep long period earthquakes that occur in the lower crust and uppermost mantle reflect the activity in the deep parts of magmatic systems here we present observations of long period earthquakes that occurred in 2011 2012 within the klyuchevskoy volcano group in kamchatka russia we show two distinct groups of long period sources events that occurred just below the active volcanoes and deep long period events at depths of 30 km in the vicinity of a deep magmatic reservoir we report systematic increases of the long period seismicity levels prior to volcanic eruptions with the initial activation of the deep long period sources that reflects pressurization of the deep reservoir and consequent transfer of the activity towards the surface the relatively fast migration of the long period activity suggests that a hydraulic connection is maintained between deep and shallow magmatic reservoirs the reported observations provide evidence for the pre eruptive reload of the shallow magmatic reservoirs from depth and suggest that the deep long period earthquakes could be used as a reliable early precursor of eruptions shallow volcanic earthquakes can aid eruption forecasts analysis of seismicity beneath the klyuchevskoy volcano group in russia reveals much deeper magma induced earthquakes that may serve as an early eruption indicator

vertical and horizontal strain partitioning of the central tianshan nw china evidence from structures and 40ar 39ar geochronology abstract as a major tectonic collage within the central asia orogen belt caob the chinese tianshan provides a natural laboratory for studying structures resulting from the amalgamation of different tectonic units detailed field and micro tectonic observations along two orogen perpendicular transects identify several structural domains with greatly variable structural styles that were generated at different structural levels but are now juxtaposed geological features combined with 40 ar 39 ar geochronologic data suggest the variable structural styles of the domains developed simultaneously during ca 320 300 ma kinematic reconstruction and deformation temperature estimation taking 40 ar 39 ar thermochronological data into account suggest both horizontal and vertical extrusion of material of the central tianshan magmatic arc assemblage ctma crust which is the expression of heterogeneous strain partitioning during orthogonal continental convergence such a kinematic scenario is quite compatible with and satisfactorily interpreted in the light of the results of available analogue deformation experiments and numerical modeling the structure styles with orthogonal symmetry of both the ctma and the southern tianshan fold and thrust belt revealed in this study in conjunction with previously published paleomagnetic data from the tarim plate suggest that the diachronous collision of the illi central tianshan micro continent with the tarim plate may have caused the tarim block rotation