a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

evidence of earthquake triggering by the solid earth tides article i nfo clearevidence forearthquake triggeringbythe earth tides hasremained elusive for morethan a century using the largest global earthquake catalog available the neic catalog with 442412 events we observe a clear correlation with 99 confidence between the phase of the solid earth tide and the timing of seismic events earthquakes occur slightly more often at the time of ground uplift by the earth tide i e when normal stresses are reduced within the lithosphere we observe that this phase distribution anomaly is larger for smaller and shallowerearthquakes although earthquakes inregionswithdominantlynormalandstrike slip faulting seem to exhibit more tidal triggering than regions dominated by thrust faulting there is no statistically significant evidence for a focal mechanism dependence on earthquake triggering finally we show here that it is highly probablethat the observedtriggeringiscaused bythe solid earth tide ratherthan byloading fromthe oceanor atmospheric tides although an additional impact due to loading from ocean tides is possible and probable we cannot detect it here because the earthquake database is not sufficiently complete and homogeneous more smallmagnitudeearthquakesinoceanicareasareneeded ourresultsareconsistentwiththeideaofadamped

re estimated effects of deep episodic slip on the occurrence and probability of great earthquakes in cascadia abstract mazzotti and adams 2004 estimated that rapid deep slip during typically two week long episodes beneath northern washington and southern british columbia increases the probability of a great cascadia earthquake by 30 100 times relative to the probability during the 58 weeks between slip events because the corresponding absolute probability remains very low at 0 03 per week their conclusion is that though it is more likely that a great earthquake will occur during a rapid slip event than during other times a great earthquake is unlikely to occur during any particular rapid slip event this previous estimate used a failure model in which great earthquakes initiate instantaneously at a stress threshold we refine the estimate assuming a delayed failure model that is based on laboratory observed earthquake initiation laboratory tests show that failure of intact rock in shear and the onset of rapid slip on pre existing faults do not occur at a threshold stress instead slip onset is gradual and shows a damped response to stress and loading rate changes the characteristic time of failure depends on loading rate and effective normal stress using this model the probability enhancement during the period of rapid slip in cascadia is negligible

seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

earthquake potential revealed by tidal influence on earthquake size frequency statistics tidal triggering of earthquakes is debated analysis of global earthquake catalogue data compared with tidal stress histories suggests that the probability of a large earthquake is greater during times of maximum tidal stress amplitude

provenance and tectonic settings of permian turbidites from the beishan mountains nw china implications for the late paleozoic accretionary tectonics of the southern altaids the beishan orogenic belt which connects the tianshan suture on the west and solonker suture on the east contains key evidence for the termination time of the southern altaids critical for evaluating different controversial tectonic models are permian marine volcaniclastic arenites in the liuyuan and heishankou areas which are dominated by greywackes and lenticular pebbly litharenites that contain grading groove marks and erosional bases which provide evidence of turbidity action sandstones from the liuyuan section are dominated by angular basaltic andesitic and feldspar fragments but sandstones from the heishankou section mainly consist of andesitic and felsic volcanic fragments these relations suggest derivation from two different sources major element compositions suggest that the source rocks of the heishankou litharenites were more sio2 rich than those at liuyuan sandstones at heishankou are characterized by lower ni co cr v and slightly higher th and la contents than those at liuyuan this indicates that the litharenites in the liuyuan and heishankou areas were derived from intermediate mafic and intermediate felsic source rocks respectively tectonic setting discrimination plots suggest that the liuyuan sandstones were deposited as detritus from an oceanic island arc but the heishankou sediments from an andean continental margin our petrological and geochemical data from these two types of permian turbidites suggest that an arc continent collision took place in the early permian and this is consistent with the permian termination of the southern altaids

simulation of the net snow accumulation along the wilkes land transect antarctica with a regional climate model regional climate modelling in conjunction with accumulation measurements collected on antarctic traverses of the international trans antarctic scientific expedition itase is presented as a tool for extending the spatial coverage of field measurements the modelling of part of east antarctica spanned the 7 year epoch 1980 86 where data covering the same period are available the agreement between simulation and observation is improved when a parameterization of the snow surface redistribution processes such as wind erosion is included in the regional climate model the modelled spatial distribution of the net snow mass transported in the boundary layer over coastal east antarctica indicates that this mass is a significant component of the surface mass balance

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

on the extraordinary katabatic winds of adelie land the winds observed in adelie land eastern antarctica are the strongest observed anywhere on earth close to sea level e g cape denison measured a mean annual wind speed of about 20 m s 1 some historic data from the area are available however such measurements were carried out at different places for different time periods hence in december 1992 we placed four automatic weather stations along the coast of adelie land two in the maximum wind jet port martin and cape denison and one on each side of this jet d 10 close to dumont d urville and penguin point respectively we obtained about three months of good data as on march 25 1993 a strong storm destroyed three of the four wind sensors wind velocities are discussed as a function of other meteorological parameters further the interrelationships between the stations are described some of the findings are 1 the very high wind speeds reported earlier this century are in agreement with our measurements the wind directional constancy is high 2 historic measurements reported cape denison to be the windiest station not only for antarctica but also close to sea level for planet earth again our measurements are in agreement 3 very strong wind speeds have a more down slope direction than weaker ones 4 the general atmospheric pressure gradient enhanced or inhibited the gravity flow this is especially well pronounced in summer and 5 in summer above normal pressure is correlated with above normal temperatures in fall the opposite holds true

absence of earthquake correlation with earth tides an indication of high preseismic fault stress rate because the rate of stress change from the earth tides exceeds that from tectonic stress accumulation tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the tectonic rate and if rupture began soon after the achievement of a critical stress level we analyze the tidal stresses and stress rates on the fault planes and at the times of 13 042 earthquakes which are so close to the san andreas and calaveras faults in california that we may take the fault plane to be known we find that the stresses and stress rates from earth tides at the times of earthquakes are distributed in the same way as tidal stresses and stress rates at random times while the rate of earthquakes when the tidal stress promotes failure is 2 higher than when the stress does not this difference in rate is not statistically significant this lack of tidal triggering implies that preseismic stress rates in the nucleation zones of earthquakes are at least 0 15 bar h just preceding seismic failure much above the long term tectonic stress rate of 10 4 bar h

evidence of both m2 and o1earth tide waves in radon 222 air concentration measured in a subglacial laboratory 1 many earthquake related radon 222 temporal changes have been recorded since the 1960s and are frequently discussed sometimes initiating a controversial debate on the relevance of radon 222 as an earthquake precursory signal the diurnal s1 o1 and semidiurnal s2 m2 earth tide signatures in radon signals are acquired in a natural context this can be used to calibrate the radon changes under strain accumulation close to epicentral areas which are often discussed but are rarely evidenced by experimental data the analysis of a 10 month time series acquired in the subglacial laboratory of the argentiere glacier mont blanc massif french alps demonstrates here the unambiguous episodic appearance of the m2 o1 waves in the radon signal with significant amplitudes of 36 and 50 bq m 3 respectively we thus prove that radon variations induced by gravitational m2 and o1 waves are detectable in a natural environment in this particular place the radon response is probably amplified by cyclic stress variations applied on the upstream side of the natural rock dam into which the laboratory is drilled the amplification of the radon signal is induced by poroelastic deformation under this particular mechanical forcing this can elucidate why most precedent studies failed to detect m2 o1 signatures in radon signals recorded in other underground laboratories

modeling and detecting interactions between earth tides and earthquakes with application to an aftershock sequence in the pyrenees abstract assuming that earthquakes are governed by solid friction and that the fault plane solutions are known a simplified model of correlation between the seismicity and a specified component of the tidal stress is proposed in the case of an earthquake sequence with a uniform time distribution and with a prevailing focal mechanism a test of statistical significance is derived from a binomial probability distribution this interaction model is checked over the aftershock sequence of a magnitude 5 earthquake which occurred within a seismic array in the pyrenees on 29 february 1980 the tidal stress field including the ocean tide effect is computed for this area the global time decrease of the seismicity is taken into account by a time transformation in order to deal with the time and space complexity of the stress field a moving window analysis is used it is shown that during one 7 day period out of a total of 30 days a positive correlation appears between earth tides and seismicity in agreement with the proposed model

deep geothermal processes acting on faults and solid tides in coastal xinzhou geothermal field guangdong china abstract this paper investigated the deep fault thermal flow processes in the xinzhou geothermal field in the yangjiang region of guangdong province deep faults channel geothermal energy to the shallow ground which makes it difficult to study due to the hidden nature we conducted numerical experiments in order to investigate the physical states of the geothermal water inside the fault zone we view the deep fault as a fast flow path for the thermal water from the deep crust driven up by the buoyancy temperature measurements at the springs or wells constrain the upper boundary and the temperature inferred from the currie temperature interface bounds the bottom the deepened boundary allows the thermal reservoir to revolve rather than to be at a fixed temperature the results detail the concept of a thermal reservoir in terms of its formation and heat distribution the concept also reconciles the discrepancy in reservoir temperatures predicted from both quartz and na k mg the downward displacement of the crust increases the pressure at the deep ground and leads to an elevated temperature and a lighter water density ultimately our results are a first step in implementing numerical studies of deep faults through geothermal water flows future works need to extend to cases of supercritical states this approach is applicable to general deep fault thermal flows and dissipation paths for the seismic energy from the deep crust

non volcanic tremor resulting from the combined effect of earth tides and slow slip events swarms of non volcanic tremor in southeastern japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h this periodicity can be reproduced by a combination of stresses due to earth tides and transient stress changes caused by slow slip events non volcanic tremors may therefore be useful for understanding stress relaxation at the subduction zone interface slow slip events1 are accompanied by swarms of non volcanic tremor2 3 along the subduction zone of the philippine sea plate in southwest japan the swarms often occur with a periodicity of about 12 or 24 h refs 4 5 these episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1 6 7 here we analyse seismic data to record the locations and durations of non volcanic tremor swarms that occurred in may 2005 and february 2006 we evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur we find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to earth tides and the transient stress due to slow slip events our calculations show that non volcanic tremor is sensitive to stress change this phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces

evidence for remotely triggered microearthquakes during salt cavern collapse summary microseismicity is a good indicator of spatio temporal evolution of physical properties of rocks prior to catastrophic events like volcanic eruptions or landslides and may be triggered by a number of causes including dynamic characteristics of processes in play or and external forces we show evidence of triggered microseismicity observed in the vicinity of an underground salt cavern prone to collapse by a remote m 7 2 earthquake which occurred 12 000 km away high dynamic range broad band records reveal the strong time correlation between a dramatic change in the rate of local high frequency microseismicity and the passage of low frequency seismic waves including body love and rayleigh surface waves pressure was lowered in the cavern by pumping operations of brine out of the cavern we demonstrate the near critical state of the cavern before the collapse by means of 2 d axisymmetric elastic finite element simulations on this basis we show that the increment of stress necessary for the failure of the dolomite layer which ensures the stability of the whole system is of the same order of magnitude as the maximum dynamic stress magnitude observed during the passage of the earthquakes waves this suggests that the stress oscillations due to the seismic waves correlated with the recorded microearthquakes induced damage of the overburden which eventually led to the collapse of the salt cavern we show that the contribution of rayleigh waves is the most efficient to trigger microseismicity at periods close to the natural fundamental frequency of the cavern system found at about 10 20 s by investigating the impulse response of the cavern overburden brine system

nucleation and triggering of earthquake slip effect of periodic stresses abstract results of stability analyses for spring and slider systems with state variable constitutive properties are applied to slip on embedded fault patches unstable slip may nucleate only if the slipping patch exceeds some minimum size subsequent to the onset of instability the earthquake slip may propagate well beyond the patch it is proposed that the seismicity of a volume of the earth s crust is determined by the distribution of initial conditions on the population of fault patches that nucleate earthquake slip and the loading history acting upon the volume patches with constitutive properties inferred from laboratory experiments are characterized by an interval of self driven accelerating slip prior to instability if initial stress exceeds a minimum threshold this delayed instability of the patches provides an explanation for the occurrence of aftershocks and foreshocks including decay of earthquake rates by time 1 a population of patches subjected to loading with a periodic component results in periodic variation of the rate of occurrence of instabilities the change of the rate of seismicity for a sinusoidal load is proportional to the amplitude of the periodic stress component and inversely proportional to both the normal stress acting on the fault patches and the constitutive parameter a 1 that controls the direct velocity dependence of fault slip values of a 1 representative of laboratory experiments indicate that in a homogeneous crust correlation of earthquake rates with earth tides should not be detectable at normal stresses in excess of about 8 mpa correlation of earthquakes with tides at higher normal stresses can be explained if there exist inhomogeneities that locally amplify the magnitude of the tidal stresses such amplification might occur near magma chambers or other soft inclusions in the crust and possibly near the ends of creeping fault segments if the creep or afterslip rates vary in response to tides observations of seismicity rate variations associated with seasonal fluctuations of reservoir levels appear to be consistent with the model

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

gravity tides extracted from relative gravimeter data by combining empirical mode decomposition and independent component analysis the static observation data from a relative gravimeter contain noise and signals such as gravity tides this paper focuses on the extraction of the gravity tides from the static relative gravimeter data for the first time applying the combined method of empirical mode decomposition emd and independent component analysis ica called the emd ica method the experimental results from the cg 5 gravimeter scintrex limited ontario canada data show that the gravity tides time series derived by emd ica are consistent with the theoretical reference longman formula and the rms of their differences only reaches 4 4 gal the time series of the gravity tides derived by emd ica have a strong correlation with the theoretical time series and the correlation coefficient is greater than 0 997 the accuracy of the gravity tides estimated by emd ica is comparable to the theoretical model and is slightly higher than that of independent component analysis ica emd ica could overcome the limitation of ica having to process multiple observations and slightly improve the extraction accuracy and reliability of gravity tides from relative gravimeter data compared to that estimated with ica

prediction of severe synoptic events in coastal east antarctica abstract the coastal region of the antarctic continent is renowned for the frequent intense blizzards and associated extreme weather that affect it creating treacherous conditions that place human activities there in often perilous situations the understanding and prediction of these events are therefore vital for continued safe operations on the continent severe wind events are investigated at two australian coastal sites casey and mawson a summer case study at casey and then the climatology of the events at the two stations are studied using station observations and atmospheric analyses all events are found to be associated with extratropical cyclones that move close to the stations and lead to strong winds and heavy cloud cover most events see the passage of a high pressure ridge over the station ahead of the cyclone that blocks the cyclone forcing it to move farther south close to the coast thus intensifying the effect of the cyclone on the coastal weather the ridge also produces calm clea

elemental and sr nd pb isotopic geochemistry of late paleozoic volcanic rocks beneath the junggar basin nw china implications for the formation and evolution of the basin basement the basement beneath the junggar basin has been interpreted either as a micro continent of precambrian age or as a fragment of paleozoic oceanic crust elemental and sr nd pb isotopic compositions and zircon pb pb ages of volcanic rocks from drill cores through the paleo weathered crust show that the basement is composed mainly of late paleozoic volcanic rock with minor shale and tuff the volcanic rocks are mostly subalkaline with some minor low k rocks in the western kexia area some alkaline lavas occur in the central luliang uplift and northeastern wulungu depression the lavas range in composition from basalts to rhyolites and fractional crystallization played an important role in magma evolution except for a few samples from kexia the basalts have low la nb 1 4 typical for oceanic crust derived from asthenospheric melts zircon pb pb ages indicate that the kexia andesite with a volcanic arc affinity formed in the early carboniferous 345 ma whereas the luliang rhyolite and the wucaiwan dacite with syn collisional to within plate affinities formed in the early devonian 395 and 405 ma respectively positive end t values up to 7 4 and low initial 87sr 86sr isotopic ratios of the intermediate silicic rocks suggest that the entire junggar terrain may be underlain by oceanic crust an interpretation consistent with the juvenile isotopic signatures of many granitoid plutons in other parts of the central asia orogenic belt variation in zircon ages for the silicic rocks different ba p ti nb or th anomalies in the mafic rocks and variable nb y and la nb ratios across the basin suggest that the basement is compositionally heterogeneous the heterogeneity is believed to reflect amalgamation of different oceanic blocks representing either different evolution stages within a single terrane or possibly derivation from different terranes

the geochemistry of archaean shales derived from a mafic volcanic sequence belingwe greenstone belt zimbabwe provenance source area unroofing and submarine versus subaerial weathering shales of the 2 7 ga zeederbergs formation belingwe greenstone belt zimbabwe form thin 0 2 2 m horizons intercalated with submarine lava plain basalts shales of the overlying cheshire formation a foreland basin sedimentary sequence form 1 100 m thick units intercalated with shallow water carbonates and deep water resedimented basalt pebble conglomerates zeederbergs shale is characterized by high contents of mgo and transition metals and low concentrations of k2o and lile as compared to average phanerozoic shale indicative of an ultramafic to mafic source terrain cheshire shales have similar major and trace element contents but mgo and transition metals are less enriched and the lile are less depleted zeederbergs shales have smoothly fractionated ree patterns lan ybn 2 84 4 45 and no significant eu anomaly eu eu 0 93 0 96 ree patterns are identical to those of the surrounding basaltic rocks indicating local derivation from submarine reworking cheshire shales have rather flat ree patterns lan ybn 0 69 2 19 and a small negative eu anomaly average eu eu 0 85 indicative of a mafic provenance with minor contributions of felsic detritus a systematic change in ree patterns and concentrations of transition metals and hfse upwards in the sedimentary succession indicates erosion of progressively more lree depleted basalts and ultramafic volcanic rocks followed by unroofing of granitoid crust weathering indices confirm the submarine nature of zeederbergs shale whereas cheshire shale was derived from a source terrain subjected to intense chemical weathering

an analysis of strong wind events simulated in a gcm near casey in the antarctic abstract strong wind events occurring near casey antarctica in a long july gcm simulation have been studied to determine the relative roles played by the synoptic situation and the katabatic flow in producing these episodes it has been found that the events are associated with strong katabatic and strong gradient flow operating together both components are found to increase threefold on average for these strong winds and although the geostrophic flow is the stronger it rarely produces strong winds without katabatic flow becoming stronger than it is in the mean the two wind components do not flow in the same direction indeed there is some cancellation between them since katabatic flow acts in a predominant downslope direction while the geostrophic wind acts across slope the stronger geostrophic flow is associated with higher than average pressures over the continent and the approach of a strong cyclonic system toward the mast and a blocking system downstream the anomalous synoptic patterns lea

tidal triggering of earthquakes analysis of the tidal stress tensor at the time of moderate to large earthquakes strongly suggests that shallow 30 km larger magnitude oblique slip and dip slip earthquakes are triggered by tidal stresses no corresponding triggering effect is seen for shallow strike slip earthquakes or for any type of intermediate or deep focus earthquakes which have been studied tidal triggering is also discussed from the viewpoint of the dilatancy diffusion model specifically the model as usually stated excludes the possibility of small earthquakes being tidally triggered

tidal triggering of earthquakes in the northeast pacific ocean summary there have been many searches for evidence of tidal triggering in earthquake catalogues with the exception of volcanically active regions the more rigorous studies in continental settings tend to find no correlation or only a very weak correlation in the oceans the effect of loading by the ocean tides can increase tidal stresses by about an order of magnitude over continental settings in recent years several studies have reported evidence of tidal triggering in oceanic regions and such observations can represent a useful constraint on models of earthquake rupture in this paper i systematically search for a link between ocean tide height and the incidence of earthquakes in the northeast pacific ocean a region of high amplitude open ocean tides the focal mechanisms of most of the earthquakes in these catalogues are unknown but it can be shown that tidal stresses will in most instances promote failure at low tides i investigate three declustered data sets comprising 1 earthquakes from 1980 to 2007 on the juan de fuca plate and in the queen charlotte fault region from land based catalogues 2 earthquakes from 1992 to 2001 on the juan de fuca plate located with the us navy s sound surveillance system sosus hydrophone array and 3 earthquakes from 1980 to 2001 south of alaska and the aleutians located with land based networks i look at the distributions of earthquakes with ocean tide phase height and tidal range and apply schuster and binomial tests and monte carlo simulations to determine if they deviate significantly from random the results show no evidence of triggering during intervals of increased tidal range but all three data sets show a significant increase in earthquake incidence at low tides the signal is particularly strong in the land based catalogue for the juan de fuca plate and queen charlotte fault regions where there is a 15 per cent increase in the rate of seismicity within 15 of the lowest tides the signal is weakest in the sosus data set which may reflect the lower average tidal range at epicentres in this data set or an analysis that is influenced by gaps in the catalogue the triggering signal in the alaska aleutian may be partially obscured by earthquakes in the aleutians where the total tidal stresses can be significantly out of phase with the ocean tide height the increase in the rates of seismicity i observe at low tides is less than observed by local networks on mid ocean ridges similar to the prediction from an analysis of global thrust earthquakes and greater than inferred by extrapolating laboratory simulations of fault failure under tidal loading

provenance and tectonic setting of late carboniferous clastic rocks in west junggar xinjiang china a case from the hala alat mountains abstract the late carboniferous palaeo tectonic setting of the west junggar region is comprised of arcs alternating with basins geochemical analysis of the sedimentary rocks associated with these arc related basins was conducted to better constrain the provenance and tectonic setting major and trace element geochemistry data of late carboniferous mudstones and sandstones in the hala alat mountains suggest that these sedimentary rocks and their source areas are characterized by the following four features 1 sediments experienced a simple recycling process 2 a low degree weathering conditions in the source areas 3 compositional immature of the sedimentary rocks 4 dominated by intermediate to felsic provenance with a few intermediate to mafic sediments integrated with the palaeo flow data and previous authors works a fore arc basin model is proposed for the tectonic setting of the sedimentary rocks the sawur arc is the primary provenance and supplies the major intermediate to felsic detrital fragments the bozchekul chingiz arc and kexia oceanic island arc are the other two secondary sources

mud volcanism an updated review abstract mud volcanism or sedimentary volcanism represents one of the most intriguing phenomena of the earth s crust with important implications in energy resource exploration seismicity geo hazard and atmospheric budget of greenhouse gases since the first review papers were issued at the beginning of 2000s a large amount of new geological geophysical and geochemical data has been acquired which clarified ambiguous concepts and significantly improved our knowledge of mud volcanism here we offer an updated review of the knowledge and implications of mud volcanoes with emphasis on the terminology used to describe different processes and structures the physical chemical and morphological characteristics of the several fluid emission structures the chemical properties of the released fluids in particular the molecular and isotopic composition of the gas the mud volcano formation dynamics and the several implications for petroleum exploration geo hazards and global atmospheric methane budget this review integrates new fluids data collected in azerbaijan and is complemented with field observations from various mud volcano provinces worldwide although the total number of mud volcanoes on earth is still uncertain 600 main onshore structures with a large variety in shapes and sizes are documented in recent global data sets and several thousand are assumed to exist in the oceans it is clear that a mud volcanoes are broadly distributed throughout the globe in active margins compressional zones of accretionary complexes thrust and overthrust belts passive margins deep sedimentary basins related to active plate boundaries as well as delta regions b they are specifically located in hydrocarbon bearing basins along anticline axes strike slips and normal faults and fault related folds in petroleum systems c they represent a specific category of natural gas oil seepage manifestation often related to deep and pressurised reservoirs d the main engine driving mud volcanism is given by a combination of gravitative instability of shales and fluid overpressure build up followed by hydrofracturing e hydrocarbons are generally of thermogenic origin while microbial gas is released in only a few cases mud volcanism on other planets e g mars and titan and microbial activity associated with gas seepage represent emerging issues and opportunities for future research

tidal modulation of plate motions abstract while mantle convection is a fundamental ingredient of geodynamics the driving mechanism of plate tectonics remains elusive are plates driven only from the thermal cooling of the mantle or are there further astronomical forces acting on them gps measurements are now accurate enough that on long baselines both secular plate motions and periodic tidal displacements are visible the now 20 year long space geodesy record of plate motions allows a more accurate analysis of the contribution of the horizontal component of the body tide in shifting the lithosphere we review the data and show that lithospheric plates retain a non zero horizontal component of the solid earth tidal waves and their speed correlates with tidal harmonics high frequency semidiurnal earth s tides are likely contributing to plate motions but their residuals are still within the error of the present accuracy of gnss data the low frequency body tides rather show horizontal residuals equal to the relative motion among plates proving the astronomical input on plate dynamics plates move faster with nutation cyclicities of 8 8 and 18 6 years that correlate to lunar apsides migration and nodal precession the high frequency body tides are mostly buffered by the high viscosity of the lithosphere and the underlying mantle whereas low frequency horizontal tidal oscillations are compatible with the relaxation time of the low velocity zone and can westerly drag the lithosphere over the asthenospheric mantle variable angular velocities among plates are controlled by the viscosity anisotropies in the decoupling layer within the low velocity zone tidal oscillations also correlate with the seismic release

provenance and tectonic setting of the carboniferous sedimentary rocks of the east junggar basin china evidence from geochemistry and u pb zircon geochronology abstract the modern junggar basin was located in the central asian orogenic belt caob during the devonian and carboniferous few data concerning the weathering provenance and tectonic setting of the carboniferous sedimentary rocks in the junggar basin have been published the recent discovery of an oil gas field in the east junggar basin provides the impetus for this study twenty eight sediment samples were recovered from eight boreholes and all were analysed for major and trace element geochemistry two samples of sedimentary rocks were selected for zircon u pb dating low chemical index of alteration cia values 44 71 and relatively high index of compositional variability icv values 0 72 1 83 suggested weak chemical weathering and an immature source for these samples the relatively low th u 2 16 10 55 and rb sr 0 03 5 44 ratios of the drill core samples reflect a simple recycling history two samples indicated upper carboniferous ages 314 6 ma and a lower middle devonian age 397 9 ma geochemistry and detrital zircon geochronology from the east junggar basin reveal a distinct difference in the composition and source rock ages of clastic rocks from the lower and the upper carboniferous major and trace element compositions of the lower carboniferous sedimentary rocks lcrs were derived from typical mafic rocks and an intermediate ocean island arc of early to middle devonian age whereas the upper carboniferous sedimentary rocks ucrs were derived from a continental island arc or active continental margin setting with a dominantly felsic to intermediate late carboniferous age the current data provide little support for tectonic models that show a passive continental margin of a precambrian crystalline basement our study suggests that a volcanic arc accretion or archipelago early carboniferous to early middle devonian model for the east junggar basin is more viable

evidence for tidal triggering of earthquakes as revealed from statistical analysis of global data 1 we observe tidal triggering of earthquakes by measuring the correlation between the earth tide and earthquake occurrence we used the times locations and focal mechanisms of the 9350 globally distributed earthquakes with magnitude 5 5 or larger from the harvard centroid moment tensor catalog the tidal stress was theoretically computed by using the preliminary reference earth model and a recent ocean tide model nao 99b we considered the shear stress on the fault plane and the trace of stress tensor j1 defining the tidal phase angle at the occurrence time for each earthquake we statistically tested the phase selectivity using the schuster s method for all the earthquakes no significant correlation is found between the earth tide and earthquake occurrence both for the shear stress and for j1 by classifying the data set according to fault types however we find a high correlation with the shear stress for reverse fault type the correlation is particularly clear for shallow and smaller earthquakes of this type significant correlation with j1 also appears for larger earthquakes of reverse fault type and for shallow and larger ones of normal fault type we find no correlation for strike slip type for all the cases of high correlation earthquakes tend to occur when the tidal stress accelerates the fault slip indicating that high correlation is not coincidental but is physically justified this result strongly suggests that a small stress change due to the earth tide encourages earthquake occurrence when the stress in the future focal area is near a critical condition

seismic triggering effect of tidal stress abstract the tidal stress field of a layered spherically symmetric earth due to the sun and moon is used to investigate its relationship to the occurrence of earthquakes for 70 severe earthquakes which occurred in or near china during the last 24 years we computed the tidal stress in spherical polar coordinates at the focus at the time of occurrence the normal and tangential stress components along the slip direction on the earthquake fault plane were then found by a coordinate transformation coulomb s criterion of shear fracture is used to determine whether these stress components will trigger the earthquakes or not the results show that of the 70 earthquakes 43 have been subjected to a triggering effect and for the 18 events that occurred in north china 14 have been triggered it may be concluded that for shallow strike slip earthquakes there is a significant triggering effect while for oblique slip and dip slip earthquakes the tidal stress has only a small triggering effect from 72 events which occurred in other parts of the world similar conclusions are obtained finally for the purpose of predicting earthquakes the time interval during which the tidal stress may trigger an earthquake on faults in north china is investigated

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

no clear evidence for localized tidal periodicities in earthquakes in the central japan region we search for possible localized tidal triggering in earthquake occurrence near japan by testing for tidal periodicities in seismicity within a variety of space time bins we examine 74 610 earthquakes of m 3 in the japan meteorological agency jma catalog from january 2000 to april 2013 because we use many earthquakes for which accurate focal mechanisms are not available we do not compute tidal stresses on individual fault planes but instead assume that the mechanisms are likely to be similar enough among nearby events that tidal triggering will promote earthquake occurrence at specific tidal phases after dividing the data into cells at a range of spatial 0 2 0 5 1 0 and temporal dimensions 100 200 400 days we apply schuster s test for non random event occurrence with respect to both the semi diurnal and semi monthly tidal phases because the resulting p values will be biased by temporal clustering caused by aftershocks we apply a declustering method that retains only one event per tidal cycle per phase increment our results show a wide range of p values for the localized earthquake bins but the number of bins with very small p values e g p 0 05 is no more than might be expected due to random chance and there is no correlation of low p value bins with the time of the 2010 m 9 0 tohoku oki earthquake

surface airflow over east antarctica abstract surface winds over the antarctic interior occur mainly due to the strong radiational cooling of the ice slopes as a consequence such winds exhibit a high degree of persistence with a predominant direction closely related to the terrain orientation using detailed contour maps of the interior ice topography and representative values of the mean wintertime strength of the temperature inversion it is possible to infer the terrain induced accelerations a simple diagnostic equation system is formulated from which a time averaged surface airflow pattern of east antarctica is generated the results appear consistent with observations the occurrence of localized anomalously strong katabatic winds is explained as a result of typographically forced patterns of cold air convergence depicted in the airflow analysis

surface pressure change through loewe s phenomena and katabatic flow jumps study of two cases in adelie land antarctica abstract preliminary results from the 1985 iago interaction atmosphere glace ocean field programme in adelie land antarctica allow for a detailed description of several katabatic events especially of their vertical structure and time and space variations several loewe s phenomena where a sudden transition from shooting to tranquil flow takes place have been observed two of them have been well documented and are shown here for both cases as observed at a downstream station close to the coast the mean wind speed suddenly decreased from about 20 m s 1 to almost zero while a large pressure increase was recorded 5 7 hpa on 3 december 1985 and 2 1 hpa on 18 december 1985 this paper aims at explaining such large surface pressure changes as more usual approaches cannot for both cases it is found that the flow is stratified upwards with a surface well mixed cold air layer a very stable capping inversion layer an overlying unstable layer thickening from upstream to downstream and a stable transi

tidal coulomb failure stresses in the northern andean intermediate depth seismic clusters implications for a possible correlation between tides and seismicity abstract a recent statistical analysis of the relationship between tides and seismic activity in colombia has suggested the existence of correlation anomalies for the case of intermediate depth events in the bucaramanga nest and the cauca cluster moncayo et al 2019 in this work we explore in detail the hypothesis that tides may be triggering seismic activity in these regions and extend the analysis to two other seismic clusters in northern central south america specifically in the areas of el puyo ecuador and pucallpa peru for this purpose we use the available focal mechanism information for seismic events at these locations and calculate for each event the tidal coulomb failure stress tcfs as obtained from estimations of the tidal strain tensor tidal strains are computed considering the earth body tides and the effect of the ocean tidal loading since our purpose is to elucidate the role of tides in earthquake nucleation calculations of the tcfs are conducted not only for the time of earthquake but also for the time of the closest maximum strain within a window of a few hours before the events our results tend to support the hypothesis that tidal stresses are contributing to earthquake generation in all the studied areas this trend is especially stronger when tcfs are calculated at pre earthquake times the physical explanation for the positive contribution of tides to earthquake triggering in intermediate depth clusters may lie in the fact that a wide diversity of fault plane orientations is possible within a relatively small volume of subducted lithosphere so making the tides more likely to help loosening up the blocks at the fault plane to promote slip

late paleozoic strike slip shear zones in eastern central asia nw china new structural and geochronological data 1 new structural studies and 40ar 39ar dating in northwest china provide information about late paleozoic strike slip motions subsequent to accretional events which built eastern central asia during the paleozoic two principal areas were affected by these large transcurrent motions first in the tianshan range main east west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism associated biotites give ages ranging from 290 ma to 245 ma the earlier n110 shearing occurred in western tianshan while the last one dextral in whole tianshan occurred 250 245 myr ago second in the chinese altay region several nw se shear zones structured the area the main motion is sinistral and occurred along the erqishi zone at 280 290 ma it is followed by a complex succession of dextral and sinistral shearing episodes leading to the northwestward structuring dated at 245 ma of a metamorphic zone that was folded during a compressive event

palaeozoic tectonics of the south western chinese tianshan new insights from a structural study of the high pressure low temperature metamorphic belt the south western chinese tianshan orogenic belt is famous for its omphacite bearing blueschists and associated eclogite facies metavolcanic rocks although numerous petrologic geochemical and geochronological studies are available structural data and interpretations are still rare this paper provides new structural data including bulk geometry of structures and kinematic analyses based on field and laboratory studies along the akyazhi keburt and muzaert rivers the study area is divided into three tectonic units namely 1 a southern unit composed of weakly metamorphosed sedimentary rocks of silurian age 2 a central hp lt unit composed of blueschist eclogite facies metamorphic rocks derived from basalts pelites and volcaniclastic rocks 3 a northern unit which consists of a carboniferous magmatic arc developed upon an amphibolite facies metamorphic continental basement our structural analysis documents a polyphase deformation the main event d1 is reflected by devonian to carboniferous top to the northwest ductile shearing coeval with hp lt metamorphism this is followed by north directed thrusting d2 of the southern unit over the central hp lt unit coeval with retrogression of the high pressure rocks a top to the s se deformation d3 overprints the earliest events and is observed in the northern and central units lastly permian dextral ductile brittle wrenching d4 overprints the older flat lying fabrics d4 is conspicuous along the nalati fault that separates the northern unit from the central hp lt unit the absolute timing of these deformation events is discussed in the light of available radiometric dating the structural metamorphic and geochronological data are integrated into a geodynamic model of the south western chinese tianshan that emphasizes south directed subduction of microcontinents located between tarim and junggar

influence of tidal forces on the triggering of seismic events tidal stresses are generated in any three dimensional body influenced by an external inhomogeneous gravity field of rotating planets or moons in this paper as a special case stresses caused within the solid earth by the body tides are discussed from viewpoint of their influence on seismic activity the earthquake triggering effects of the moon and sun are usually investigated by statistical comparison of tidal variations and temporal distribution of earthquake activity or with the use of mathematical or experimental modelling of physical processes in earthquake prone structures in this study the magnitude of the lunisolar stress tensor in terms of its components along the latitude of the spherical surface of the earth as well as inside the earth up to the core mantle boundary were calculated for the prem dziewonski and anderson in phys earth planet inter 25 4 297 356 1981 results of calculations prove that stress increases as a function of depth reaching a value around some kpa at the depth of 900 1500 km well below the zone of deep earthquakes at the depth of the overwhelming part of seismic energy accumulation around 50 km the stresses of lunisolar origin are only 0 0 1 0 103 pa despite the fact that these values are much smaller than the earthquake stress drops 1 30 mpa kanamori in annu rev earth planet sci 22 207 237 1994 this does not exclude the possibility of an impact of tidal forces on outbreak of seismic events since the tidal potential and its derivatives are coordinate dependent and the zonal tesseral and sectorial tides have different distributions from the surface down to the cmb the lunisolar stress cannot influence the break out of every seismological event in the same degree the influencing lunisolar effect of the solid earth tides on earthquake occurrences is connected first of all with stress components acting parallel to the surface of the earth the influence of load tides is limited to the loaded area and its immediate vicinity

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

fortnightly modulation of san andreas tremor and low frequency earthquakes earth tides modulate tremor and low frequency earthquakes lfes on faults in the vicinity of the brittle ductile seismic aseismic transition the response to the tidal stress carries otherwise inaccessible information about fault strength and rheology here we analyze the lfe response to the fortnightly tide which modulates the amplitude of the daily tidal stress over a 14 d cycle lfe rate is highest during the waxing fortnightly tide with lfes most strongly promoted when the daily stress exceeds the previous peak stress by the widest margin this pattern implies a threshold failure process with slip initiated when stress exceeds the local fault strength variations in sensitivity to the fortnightly modulation may reflect the degree of stress concentration on lfe producing brittle asperities embedded within an otherwise aseismic fault

frequency dependence of delayed and instantaneous triggering on laboratory and simulated faults governed by rate state friction earthquake triggering by transient stresses is commonly observed however some aspects remain unexplained the first is the often observed delay between the triggered earthquakes and the triggering waves and the second is the unexpected effectiveness of transient stressing in the seismic frequency band previous theoretical and laboratory studies have suggested that seismic transients should have little impact on faults if the duration of the transient is smaller than the timescale for nucleation of slip we reexamine the dynamics of stress triggering during stick slip sliding on a laboratory fault and make three important observations that pertain to earthquake triggering 1 delayed triggering clock advance occurs for both bare granite surfaces and granular gouge prior to the onset of instantaneous triggering 2 triggering occurs much earlier in the stick slip cycle than expected for a simple coulomb stress threshold 3 shorter period higher stressing rate pulses are more effective at triggering than longer period pulses of the same stress amplitude we use numerical simulations to show that rate state friction can explain each of the observed features but not all three simultaneously only the ruina slip law for state evolution in which faults must slip to heal can reproduce early onset and stressing rate dependent triggering the laboratory and numerical experiments show that faults can remain relatively weak over much of the seismic cycle and that the triggered response depends on a competition between healing and weakening during triggered slip transient stressing at seismic frequencies may be more effective at triggering earthquakes than previously recognized

constraints on friction dilatancy diffusivity and effective stress from low frequency earthquake rates on the deep san andreas fault author s beeler nm thomas a burgmann r shelly d abstract 2017 american geophysical union all rights reserved families of recurring low frequency earthquakes lfes within nonvolcanic tremor on the san andreas fault in central california are sensitive to tidal stresses lfes occur at all levels of the tides are strongly correlated and in phase with the 200 pa shear stresses and weakly and not systematically correlated with the 2 kpa tidal normal stresses we assume that lfes are small sources that repeatedly fail during shear within a much larger scale aseismically slipping fault zone and consider two different models of the fault slip 1 modulation of the fault slip rate by the tidal stresses or 2 episodic slip triggered by the tides lfes are strongly clustered with duration much shorter than the semidiurnal tide they cannot be significantly modulated on that time scale the recurrence times of clusters however are many times longer than the semidiurnal leading to an appearance of tidal triggering in this context we examine the predictions of laboratory observed triggered frictional dilatant fault slip the undrained end member model produces no sensitivity to the tidal normal stress and slip onsets are in phase with the tidal shear stress the tidal correlation constrains the diffusivity to be less than 1 10 6 s and the product of the friction and dilatancy coefficients to be at most 5 10 7 orders of magnitude smaller than observed at room temperature in the absence of dilatancy the effective normal stress at failure would be about 55 kpa for this model the observations require intrinsic weakness low dilatancy and lithostatic pore fluid

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

analysis of temporal variation of earthquake occurrences in caucasus from 1960 to 2011 abstract frequency of earthquake occurrences in caucasus is investigated on hourly and daily time scales the observation period is 51 years which is sufficiently long to perform a reliable statistics several methods power spectrum wavelet and hilbert huang transformation are applied to earthquake time series our findings show that earthquakes hourly and daily occurrence is not characterized by the dominant frequencies however many different oscillations with periods from hours to years and longer contribute to the frequency content of the earthquake time distribution although their amplitude is rather low the variation of the power of cyclic components in the temporal features of earthquakes occurrence is not uniform but their amplification corresponds to the decrease of released local seismic energy

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults