locating non volcanic tremor along the san andreas fault using a multiple array source imaging technique summary non volcanic tremor nvt has been observed at several subduction zones and at the san andreas fault saf tremor locations are commonly derived by cross correlating envelope transformed seismic traces in combination with source scanning techniques recently they have also been located by using relative relocations with master events that is low frequency earthquakes that are part of the tremor locations are derived by conventional traveltime based methods here we present a method to locate the sources of nvt using an imaging approach for multiple array data the performance of the method is checked with synthetic tests and the relocation of earthquakes we also applied the method to tremor occurring near cholame california a set of small aperture arrays i e an array consisting of arrays installed around cholame provided the data set for this study we observed several tremor episodes and located tremor sources in the vicinity of saf during individual tremor episodes we observed a systematic change of source location indicating rapid migration of the tremor source along saf

the effect of low velocity sediments on the mislocation vectors of the grf array summary the grf array is situated on jurassic limestone of the franconian alb in se germany the mislocation vectors show symmetry axes in their slowness and azimuth components for the slowness the line of separation is at about 95 against north the azimuth pattern shows a symmetry axis nearly perpendicular to the axis in the slowness pattern waves arriving from ne have a reduced slowness whereas waves from sw have a larger slowness the largest azimuth anomalies are found in the directions where the slowness components change direction these effects can to a large extent be modellfd by a low velocity sedimentary layer dipping to nne with about 0 8 dip such a sedimentary wedge correlates well with the geological data is able to reproduce the observed mislocation vector pattern and explains a major part of the observed traveltime residuals it furthermore demonstrates that local effects like the influence of sedimentary covers should be removed before inversion procedures and tomographic methods are applied

double beam imaging mapping lower mantle heterogeneities using combinations of source and receiver arrays we present a new technique for imaging spatially distributed heterogeneities using information from combinations of source and receiver arrays the method is based on the single scattering assumption and is closely related to the double beam method of kruger et al 1993 1995 1996 in that it exploits amplitude delay time slowness and azimuth information in two arrays simultaneously a crucial step in the method is the application of static time corrections for a chosen reference phase here pcp one type of image is obtained as a spatial likelihood distribution for prescribed source and receiver array slowness and azimuth values and delay times with respect to a reference phase this allows the determination of the spatial origin of coherent phases in the p coda in a complementary approach we perform a double beam stack migration according to the theoretical slowness and azimuth values for candidate scatterers distributed over a three dimensional 3 d grid the scattering strength is expressed as the resulting beam power beam amplitude or semblance in a time window determined from the theoretical delay time with respect to the reference phase while likelihood mapping provides an image reflecting the probability of a region to explain observed kinematic phase properties by single scattering double beam migration provides information about the scattering strength the method is applied to nuclear explosion sources in eastern kazakhstan recorded at the yellowknife array in northern canada we identify several scattering volumes within the lower mantle below the arctic producing individual anomalous lower mantle phases in the p coda these anomalies range in depth from the core mantle boundary cmb up to 500 km into the lowermost mantle and are mainly located under the eurasian side of the arctic the joint interpretation of these results with the results of previous studies suggests a connection of these anomalies to the cenozoic and mesozoic subduction of the pacific plate and the kula plate the determination of the nature of such 3 d anomalies necessitates further array studies with better azimuthal coverage

earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod 1 arrival time data from 453 local earthquakes and 6 explosions at parkfield ca are inverted for earthquake locations and three dimensional vp and vp vs structure the structure is dominated by the velocity contrast across the saf with the southwest side about 20 25 faster consistent with previous studies nearly all the earthquakes occur almost directly beneath the fault trace we find high vp vs anomalies that correlate with low resistivity features in a magnetotelluric model that are interpreted to represent fluids we locate a magnitude 2 earthquake that is a potential target event for the final stage of safod drilling yielding a depth of 3 1 km below surface and an epicenter 100 m southwest of the fault trace nonlinear analyses indicate 95 confidence relative and absolute uncertainties on the order of 500 700 m vertically and 200 300 m horizontally for this target earthquake

analysis of asymmetric multipathing with a generalization of the double beam method abstract an array method integrating source and receiver array beamforming is presented the method is a generalization of previous work kruger et al 1993 to independent variation of slowness and azimuth in both the source and the receiver array compared to the analysis capabilities of a single array the resolution is enhanced and asymmetric scattering configurations and multipathing can be studied the generalized double beam method dbm is applied to a data set consisting of nuclear explosions detonated in eastern kazakhstan and recorded at the yellowknife array in northern canada the multipathing found for pcp and pdp is interpreted in terms of lateral inhomogeneity in the lowermost mantle below severnaya zemlya indications for rayleigh to p wave scattering observed for the shagan river and degelen subsites of the former main test site of the ussr in eastern kazakhstan can be related to the structure in the vicinity of the two subsites

double beam analysis of anomalies in the core mantle boundary region seismic p waves from nuclear explosions at the kazakhstan test site in eastern kazakhstan kts observed at the yellowknife array yka canada are used to analyze the structure at the base of the mantle under severnaya zemlya arctic sea 18 events at the degelen subsite and 9 events at the shagan river subsite of kts are studied the simple waveforms and well controlled source parameters of nuclear explosions allow the use of the events as source arrays in addition to the usual receiver array configuration a new method double beamforming integrating both concepts is presented this method increases the resolution considerably for the degelen yka path one anomalous arrival 1 9 s before pcp slowness between p and pcp slowness is observed smaller anomalous arrivals are found 6 5 s degelen yka and 8 1 s before pcp shagan river yka these anomalous phases cannot be explained with standard earth models they are produced by reflections from an inhomogeneity in the lowermost mantle at 82 3n 107 5e under the area north of severnaya zemlya the strong variations between the wavefields for the two source receiver combinations indicate a heterogeneous structure in the lower mantle the anomaly found here is located close to an anomaly in the lowermost mantle beneath the nansen basin

finite difference calculation of traveltimes in three dimensions the traveltimes of first arriving seismic rays through most velocity structures can be computed rapidly on a three dimensional numerical grid by finite difference extrapolation head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 11 percent are found between the results of this technique and ray tracing for a complex but smooth model this scheme has proven useful for earthquake location and shows promise as an inexpensive well behaved substitute for ray tracing in forward modeling and kirchhoff inversion applications

reflections from a distant subduction zone accurate models of the distribution of heterogeneities in the earth s mantle especially of subduction zones are crucial for our understanding of the composition and dynamics of the earth here we present broad band bb seismograms with p waves reflected at the subduction zone under southern japan at about 84 distance from german regional seismic network the earthquakes occurred in the mariana islands region at 100 to 105 distance array techniques allow the separation of this wave with an asymmetric path p1p2 from reflections and conversions under the source the receivers and the midpoint between the source and the receivers our observation demonstrates that subduction zones can act as strong seismic reflectors and can be mapped with a depth resolution of 20km with bb arrays at teleseismic distances the analysis of such data will help to derive a more detailed picture of the structure of the earth s mantle

array analysis and precise source location of deep tremor in cascadia 1 we describe a new method to estimate the s p time of tremor like signals and its application to the nonvolcanic tremor recorded in july 2004 by three dense arrays in cascadia the cross correlation between vertical and horizontal components indicates that very often the high amplitude tremor signal contains sequences of p and s waves characterized by constant s p times ts p in the range 3 5 7 s a detailed observation of the three component seismograms stacked over the array stations confirms the presence of p and s wave sequences the knowledge of the ts p poses a strong constrain on the source array distance which dramatically reduces the uncertainty on source locations when used with more traditional array processing techniques data were analyzed using the zero lag cross correlation technique zlcc to estimate the propagation properties of the most correlated phases in the wavefield detailed polarization analyses were computed using the covariance matrix method in the time domain polarization parameters joint with the results of zlcc allows for the discrimination between p and s coherent waves results show that the tremor wavefield is composed mostly by shear waves although a consistent amount of coherent p waves is often observable the comparison of the back azimuth at the three arrays indicate that the source of deep tremor migrates over a wide area and often many independent sources located far from each other are active at the same time the tremor source was located by a probabilistic method that uses the results of zlcc given a velocity model when available the inclusion of the ts p time in the location procedure strongly reduces the depth range with a distribution of hypocenters very near the subduction interface this result significantly different compared with previous less precise locations makes the cascadia nonvolcanic tremor more similar to the nonvolcanic tremor recorded in japan at least in cases of measurable ts p the polarization azimuth aligned with the slow slip direction and the source located on the plate interface indicate that deep tremor and slow slip are two different manifestations of a common phenomenon related with the subduction dynamics

crustal scattering at the ktb from a combined microearthquake and receiver analysis summary in december of 1994 a fluid injection experiment which triggered several hundreds of microearthquakes was conducted at the ktb main borehole oberpfalz germany these events were recorded with a temporal seismic network at the surface out of the complete data set a cluster of five events recorded at four mini arrays consisting of eight or nine stations was used to investigate the crustal scattering properties in the vicinity of the ktb for this purpose the double beam method dbm kruger et al 1993 1995 1996 and the double beam imaging method scherbaum kruger weber 1997 were extended to curved wave fronts to drop the restriction of plane wave propagation this technique is used for imaging the crustal scattering strength using earthquake clusters recorded at close by mini arrays the results of the array analysis show that the composition of the p coda is mainly avected by the site location of the arrays near surface and deeper crustal scattering contribute in a very complicated pattern furthermore with the present data set it was possible to identify reflections from the top of the erbendorf body this is a very pronounced arrival in most of the recorded traces in one of the arrays its amplitudes are even greater than the direct p phases five to eight coherent phases could be identified by the mini arrays using only these phases synthetic p coda traces were constructed which only contain the coherent part of the observed wavefield by subtracting the synthetic coherent wavefield from the original traces we achieve a variance reduction in the p coda of up to 37 per cent this leads to the conclusion that a large amount of the p coda at the ktb can be modelled by a simple deterministic single scattering model using a small number of individual scatterers

paradoxical pseudotachylyte fault melt outside the seismogenic zone abstract fault generated melt pseudotachylyte is an established indicator of palaeoseismic faulting the existing consensus that frictionally induced melting occurs within the classic seismogenic zone contrast the contention over how pseudotachylyte forms within the ductile regime central to this issue is whether all pseudotachylyte originates as pressure dependent frictional melt along slip surfaces or if pressure independent processes have roles in its formation propagation of high velocity slip into deeper crustal levels provides a satisfactory explanation for pseudotachylyte at depth but does not of itself rationalize earthquake nucleation outside the classic seismogenic zone pseudotachylyte from the minas fault zone nova scotia canada is used to demonstrate the formation and preservation of fault related melt under lower crustal conditions microstructures retain evidence of intense dislocation glide with minimal climb and ductile disaggregation of the host the latter are consistent with intracrystalline deformation in the peierls stress controlled glide regime it remains unclear whether the crystal plasticity serves only as a precursory stage to rupture and high velocity slip or is itself responsible for both instability and the thermal transient there are similarities between accelerating plastic slip leading to rupture and aseismic creep bursts tremor that emphasize the mechanistic complexity of deep faulting and the need to extend consideration beyond that of a simple brittle ductile response the occurrence of tremor bursts fall within the depth range of paradoxical pseudotachylyte and provides a circumstantial link between active tectonics and the geologic record that merits examination

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

precise location of san andreas fault tremors near cholame california using seismometer clusters slip on the deep extension of the fault 1 we examine a 24 hour period of active san andreas fault saf tremor and show that this tremor is largely composed of repeated similar events utilizing this similarity we locate the subset of the tremor with waveforms similar to an identified low frequency earthquake lfe master template located using p and s wave arrivals to be 26 km deep to compensate for low signal to noise we estimate event pair differential times at clusters of nearby stations rather than at single stations we find that the locations form a near linear structure in map view striking parallel to the saf and near the surface trace therefore we suggest that at least a portion of the tremor occurs on the deep extension of the fault likely reflecting shear slip similar to subduction zone tremor if so the saf may extend to the base of the crust 10 km below the deepest regular earthquakes on the fault

cascadia tremor located near plate interface constrained by s minus p wave times nonvolcanic tremor is difficult to locate because it does not produce impulsive phases identifiable across a seismic network an alternative approach to identifying specific phases is to measure the lag between the s and p waves we cross correlate vertical and horizontal seismograms to reveal signals common to both but with the horizontal delayed with respect to the vertical this lagged correlation represents the time interval between vertical compressional waves and horizontal shear waves measurements of this interval combined with location techniques resolve the depth of tremor sources within 2 kilometers for recent cascadia tremor the sources locate near or on the subducting slab interface strong correlations and steady s p time differences imply that tremor consists of radiation from repeating sources

spatio temporal source characteristics of the 26 december 2004 sumatra earthquake as imaged by teleseismic broadband arrays 1 we test the capability of broadband arrays at teleseismic distances to image the spatio temporal characteristics of the seismic energy release during the dec 26 2004 sumatra earthquake at early observation times using a non plane wave array location technique previously reported values for rupture length about 1150 km duration about 480 s and average rupture velocity 2 4 2 7 km s are confirmed three dominant energy releases are identified one near the hypocenter a second at 6 n 94 e about 130 s later and a third one after 300 s at 9 n 92 93 e the spatio temporal distribution of the radiated seismic energy in the source region is calculated from the stacked broadband recordings of two arrays in germany and japan and results in rough estimates of the total seismic energy of 0 55 1018 nm grsn and 1 53 1018 nm fnet respectively changes in the relative ratio of energy as function of spatio temporal location indicate a rotation of the focal mechanism during the rupture process

analysis of near source contributions to early p wave coda for underground explosions iii inversion for isotropic scatterers a systematic array processing analysis is applied to 916 teleseismic shortperiod p wave signals from 25 underground explosions at pahute mesa in order to establish whether coherent arrivals scattered from near source velocity heterogeneity can be identified the signal coherence is measured using semblance which can be statistically evaluated using the noncentral f distribution if the noise properties are suitable the effects of unsuitable correlated noise due to common path and receiver contributions are suppressed by applying station weighting functions obtained by stacking all observations at a given receiver similar corrections for individual events are applied to reduce biases due to variations in surface reflection times and spall effects the characteristics of the spatial and phase velocity resolution of the semblance analysis are established by a series of synthetic calculations including cases with random arrivals in the p wave coda the procedure is applied to the actual data under the assumption that any scattering structures present radiate isotropically although this constraint could be relaxed given independent knowledge of a particular scatterer s nature the pahute mesa data show some evidence for enhanced scattering contributions to the first 15 sec of the p wave signals from the western edge of the silent canyon caldera the overall confidence level in this interpretation is fairly low because simulations with random scattering in the p coda successfully match many features observed in the stacked data

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

possible deep fault slip preceding the 2004 parkfield earthquake inferred from detailed observations of tectonic tremor 1 earthquake predictability depends in part on the degree to which sudden slip is preceded by slow aseismic slip recently observations of deep tremor have enabled inferences of deep slow slip even when detection by other means is not possible but these data are limited to certain areas and mostly the last decade the region near parkfield california provides a unique convergence of several years of high quality tremor data bracketing a moderate earthquake the 2004 magnitude 6 0 event here i present detailed observations of tectonic tremor from mid 2001 through 2008 that indicate deep fault slip both before and after the parkfield earthquake that cannot be detected with surface geodetic instruments while there is no obvious short term precursor i find unidirectional tremor migration accompanied by elevated tremor rates in the 3 months prior to the earthquake which suggests accelerated creep on the fault 16 km beneath the eventual earthquake hypocenter

locating the sources of volcanic explosions and volcanic tremor at stromboli volcano italy using beam forming on diffraction hyperboloids abstract the wave field of volcano induced seismic signals at stromboli volcano italy was observed using a network of four broadband seismometers in addition to the standard spectral analysis of the recorded signals new spectral techniques such as wavelet transform and wavelet coherence analysis were also used in order to discriminate between signals related to volcanic tremor and volcanic explosions the common features of these two types of signals are characterised by the maximum of the power spectral density values located in the frequency band 2 0 hz and the main orientation of the principal axes of the particle motion ellipsoids in the frequency bands analysed the seismic signals of the volcanic explosions at stromboli cover the total frequency band whereas the spectral content of the volcanic tremor is restricted to narrow frequency bands ranging from 0 3 5 0 hz in order to localize both types of signals a modified inversion technique was used the result of this beam forming on diffraction hyperboloids of both types of signals reveal a surprisingly shallow source location ranging from 0 2 km 0 7 km above sea level suggesting that the sources of the volcanic explosions as well as of the volcanic tremor are restricted to the uppermost parts of the volcano this is in agreement with several nonseismological observations of this volcano the combination of spectral analysis of volcanic tremor and volcanic explosions with the analysis of ground displacement implies a mechanism which can be described by an ascending bubble of volcanic gas in a nearly closed volcanic system and finally the forced ejection of the material through a narrow channel at the top of the magma column

variations in slow slip moment rate associated with rapid tremor reversals in cascadia during large slow slip events tremor sometimes propagates in the reverse along strike direction for a few hours at speeds 10 to 40 times faster than the forward propagation we examine the aseismic slip that underlies this rapidly propagating tremor we use pbo plate boundary observatory borehole strainmeter data to search for variations in the slow slip moment rate during 35 rapid tremor reversals rtrs that occurred beneath vancouver island the strain records reveal that on average the strain rate increases by about 100 30 during rtrs given the green s functions expected for slip in the rtr locations these strain rate increases imply 50 to 130 increases in the aseismic moment rate the median moment released per rtr is between 8 and 21 of the daily slow slip moment equivalent to that of a mw 5 0 to 5 1 earthquake by combining the rtr moments with the spatial extents suggested by tremor we estimate that a typical rtr has peak slip of roughly one sixth of the peak slip in the main slow slip event near front slip rate of a few to ten times the main front slip rate stress drop around half the main event stress drop and strain energy release rate around one tenth that of the main front our observations support a picture of rtrs as aseismic subevents with high slip rates but modest strain energy release rtrs appear to contribute to but not dominate the overall slow slip moment though they may accommodate most of the slip in certain locations

traveltime and amplitude anomalies at the seismic broad band may grf summary traveltime and amplitude residuals of p waves from teleseismic events show a positive correlation at the stations of the german seismic broad band array grf fast arrivals consistently have reduced amplitudes in the four frequency ranges considered short period bandpass wwssn sp filter broad band velocity and wwssn lp filter with the exception of the wwssn lp filter 40 60 per cent of the average of the relative traveltime and almost 100 per cent of the average of the amplitude residuals at individual stations with respect to the reference station a1 can be explained by near surface sediment layers these shallow structures are known from local and regional geology and are documented in borehole local refraction and polarization studies this aximuthal and distance independent term station average reaches values of up to 0 55 s and 0 15 units in log amplitude magnitude even after the removal of these station averages which also contain a trend of increasing crustal and uppermost mantle velocity from north to south large azimuthal and distance dependent relative traveltime and magnitude residuals can be observed across the array these residuals vary between 0 8 and 1 1 s and 0 54 and 0 72 magnitude units negative fast traveltime residuals are again related to negative magnitude residuals small amplitudes the azimuthal and distance dependent patterns of these residuals are identical within three distinct clusters of stations the main features of the residual patterns correlate well with the main fault systems and inhomogeneities near the array some of which have been postulated previously the velocity anomalies causing the azimuthal and distance dependent residuals are located in crust and uppermost mantle under the array and its vicinity the fact that local effects like sedimentary covers are responsible for 40 per cent or more of the station average residuals demonstrates again that site effects should be removed before tomographic methods are employed the simple stations corrections usually applied in global tomography might severely underestimate the influence of local and regional velocity anomalies since even after the removal of the station average residual large azimuthal and distance dependent traveltime and amplitude anomalies remain between stations less than 100 km apart these anomalies due to shallow inhomogeneities might then erroneously be mapped into features at greater depth

array measurements of deep tremor signals in the cascadia subduction zone 1 preliminary analysis of deep tremor recorded during july 2004 in the cascadia subduction zone shows that small aperture arrays can resolve the slowness and back azimuth of seismic waves with a useful resolution data were collected by three dense arrays of short period seismometers specifically deployed in the puget sound area under an us italy canada cooperative effort slowness analyses at the three arrays indicate that the 2 4 hz tremor wave field is composed of waves propagating with apparent velocities higher than 4 km s combining this with polarisation analysis show these waves to be transverse sh waves however p waves though smaller in amplitude can be detected by different slowness values obtained for the radial and transverse components the intersection of wave vectors determined by the back azimuth and slowness values measured at the three arrays provides a preliminary estimate of source location for a sample of the recorded deep tremor

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

array analysis using circular wave front geometry an application to locate the nearby seismo volcanic source summary the zero lag cross correlation technique used for array analysis in the hypothesis of plane waves has been modified to allow the wave front to be circular synthetic tests have been performed to check the capability of the method which returns the input test data when the source array distances are not greater than two or three times the array aperture for this distance range the method furnishes an estimate of the apparent velocity and the epicentral coordinates of the source for more distant sources the method becomes equivalent to that based on the planar wave approximation which gives an estimate of the backazimuth to the source and the apparent velocity the method has been applied to seismic data recorded at the active volcano located at deception island antarctica 35 volcanic long period events occurring in a small swarm were selected results show that the epicentres are close to the array between 0 4 and 2 km and aligned in a sw direction in agreement with one of the main directions of the fracture system of deception volcano

studies of the seismic coda using an earthquake cluster as a deeply buried seismograph array loosely speaking the principle of green s function reciprocity means that the source and receiver positions in a seismic experiment can be exchanged without affecting the observed seismograms consequently the seismograms observed at a single observation location o and caused by a cluster of microearthquakes at locations ei are identical to the time series that would be measured by an array of stress meters emplaced at positions ei recording waves generated by a source acting at o by applying array analysis techniques like slant stacking and frequency wave number analysis to these seismograms we can determine the directions and velocities of the component waves as they travel in the earthquake focal region rather than at the surface we have developed a computationally rapid plane wave decomposition which we have applied to single station recordings of aftershocks of the 1984 morgan hill california earthquake the analysis is applied to data from three seismic stations having considerably different site geologies one is a relatively hard rock station situated on franciscan metamorphics one is within the calaveras fault zone and one is on semiconsolidated sand and gravels we define the early coda to be the part of the coda initiating immediately after the direct s wave and ending at twice the s wave lapse time the character of the s wave and early coda varies from being impulsive at the first station to highly reverberative at the last we examine waves in sequential time windows starting at the s wave and continuing through the early part of the coda at all seismic stations the early coda is dominated by a persistent signal that must be caused by multiple scattering probably within 2 km of each seismic station despite clear station to station differences in the character of the early coda coda q values measured in the late coda greater than twice the s lapse time agree well among stations implying that the mechanisms causing the varying behavior of the early coda do not control the coda decay rate at the stations we have considered coda q values measured on horizontal components of motion agree within a factor of 2 with those measured on vertical components we have not been able to determine the composition of the late coda because of a low signal to noise ratio our analysis technique however is quite appropriate for such a task

a 15 year catalog of more than 1 million low frequency earthquakes tracking tremor and slip along the deep san andreas fault low frequency earthquakes lfes are small rapidly recurring slip events that occur on the deep extensions of some major faults their collective activation is often observed as a semicontinuous signal known as tectonic or nonvolcanic tremor this manuscript presents a catalog of more than 1 million lfes detected along the central san andreas fault from 2001 to 2016 these events have been detected via a multichannel matched filter search cross correlating waveform templates representing 88 different lfe families with continuous seismic data together these source locations span nearly 150 km along the central san andreas fault ranging in depth from 16 to 30 km this accumulating catalog has been the source for numerous studies examining the behavior of these lfe sources and the inferred slip behavior of the deep fault the relatively high temporal and spatial resolutions of the catalog have provided new insights into properties such as tremor migration recurrence and triggering by static and dynamic stress perturbations collectively these characteristics are inferred to reflect a very weak fault likely under near lithostatic fluid pressure yet the physical processes controlling the stuttering rupture observed as tremor and lfe signals remain poorly understood this paper aims to document the lfe catalog assembly process and associated caveats while also updating earlier observations and inferred physical constraints the catalog itself accompanies this manuscript as part of the electronic supplement with the goal of providing a useful resource for continued future investigations

detection method for pairs of p and s waves of deep low frequency earthquakes using a 3 d array in the tokai area of the nankai subduction and its application to hypocenter determination

nickel copper occurrences in the belleterre angliers belt of the pontiac subprovince and the use of cu pd ratios in interpreting platinum group element distributions within the belleterre angliers greenstone belt of the pontiac subprovince there are a number of ni cu sulfide occurrences associated with synvolcanic gabbros the stratigraphy and geochemistry of the belt suggest that it is a rifted island arc and that the gabbros which contain the ni cu sulfides were derived from the mantle plume that rifted the island arc the conditions under which the sulfides formed may be modeled either by recalculating the sulfide compositions to 100 percent sulfide or by using the cu pd ratios both approaches suggest that most of the sulfide occurrences formed from an enriched morb magma with r factors of 200 to 1 000 one of the occurrences la force is depleted in platinum group elements pge relative to cu and this depletion may be the result of the removal of sulfides from the magma prior to emplacement at this stratigraphic level the advantage of using the cu pd ratio rather than recalculating to 100 percent sulfide is that it is not necessary to have s analyses to model the conditions of formation of the sulfides further the cu pd ratio may be used as a prospecting tool rocks with ratios greater than mantle values formed from magmas depleted in pd possibly due to removal of sulfide from the magma this implies the potential for a pge bearing sulfide deposit at stratigraphically lower levels such an approach has been applied to pge targets in the eastern abitibi subprovince samples from four ni cu occurrences with cu pd ratios close to mantle ratios have the potential to produce pge as a by product samples from seven ni cu sulfide occurrences and the layered intrusions lac dore bell river and cummings complex have cu pd ratios much greater than mantle ratios indicating that these intrusions and sulfides are not good targets for pge at this stratigraphic level although there may be pge rich sulfides present at depth

fast location of seismicity a migration type approach with application to hydraulic fracturing data we propose a new approach for the location of seismic sources using a technique inspired by gaussian beam migration of three component data this approach requires only the preliminary picking of time intervals around a detected event and is much less sensitive to the picking precision than standard location procedures furthermore this approach is characterized by a high degree of automation the polarization information of three component data is estimated and used to perform initial value ray tracing by weighting the energy of the signal using gaussian beams around these rays the stacking is restricted to physically relevant regions only event locations correspond to regions of maximum energy in the resulting image we have successfully applied the method to synthetic data examples with 20 30 white noise and to real data of a hydraulic fracturing experiment where events with comparatively small magnitudes 0 were recorded

continental transforms a view from the alpine fault abstract continental transform faults are dominantly highly localized strike slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement from work on the alpine fault we pose the questions what is the deep structure of a continental transform and how does the displacement become localized we review research on the alpine fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault parallel motion and a flat ductile decollement in the lower crust the fault localizes around two thirds of the plate motion within a 100 km wide zone of distributed deformation a review of other active continental fault systems suggests that variation between them may reflect their tectonic origins the nature of the crust in which they develop the presence of a significant oblique component of motion and the displacement rate all however have evidence for the development of a single principal fault zone that carries 50 of the total displacement and extends as a localized zone of shear into the upper mantle we review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle

upper mantle seismic discontinuities and the thermal structure of subduction zones the precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western united states the boundary near 410km depth is locally elevated that near 660 km depressed the depths of these boundaries which mark phase transitions provide an in situ thermometer in subduction zones the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth in addition a reflector near 210 km depth may mark the bottom of the aesthenosphere

array analysis of the seismic wavefield of long period events and volcanic tremor at arenal volcano costa rica we use wavefield decomposition methods time domain crosscorrelation and frequency domain music to analyze seismic data recorded by a dense small aperture array located 2 km west of arenal volcano costa rica and operated during 2 5 days the recorded wavefield is dominated by harmonic tremor and includes also spasmodic tremor and long period lp events we find that the initial stages of lp events are characterized by three different wave arrivals these arrivals propagate with similar back azimuths pointing to the volcano summit 80 n and increasing apparent slownesses of 0 4 1 1 and 1 7 s km spasmodic tremors can not be regarded as coherent signals on the contrary harmonic tremors are highly coherent characterized by the stability of the apparent slowness vector estimates apparent slownesses lay in the range 1 2 s km back azimuths point in the general direction of the volcano but with a large variability 40 120 n nevertheless there are long term variations and evidences of multiple simultaneous components in the harmonic tremor wavefield these observations suggest that lp events and tremor are generated in a shallow source area near the volcano summit although they do not share exactly the same source region or source processes the tremor source is located in the shallowest part of the plumbing system beneath the lava crust this dynamic region is subject to complex fluctuations of the physical conditions degassing events at different locations of this region might generate variable seismic radiation patterns the effects of topography and heterogeneous shallow structure of the volcano may amplify these variations and produce the wide directional span observed for volcanic tremor on the other hand the lp source seems to be more repeatable lp events are likely triggered by fragmentation of the fluid flow in a slightly deeper portion of the volcanic conduits

nonvolcanic tremors deep beneath the san andreas fault we have discovered nonvolcanic tremor activity i e long duration seismic signals with no clear p or s waves within a transform plate boundary zone along the san andreas fault near cholame california the inferred epicentral region of the 1857 fort tejon earthquake moment magnitude 7 8 the tremors occur between 20 to 40 kilometers depth below the seismogenic zone the upper 15 kilometers of earth s crust where earthquakes occur and their activity rates may correlate with variations in local earthquake activity

san andreas fault zone head waves near parkfield california microearthquake seismograms from the borehole seismic network on the san andreas fault near parkfield california provide three lines of evidence that first p arrivals are head waves refracted along the cross fault material contrast first the travel time difference between these arrivals and secondary phases identified as direct p waves scales linearly with the source receiver distance second these arrivals have the emergent wave character associated in theory and practice with refracted head waves instead of the sharp first breaks associated with direct p arrivals third the first motion polarities of the emergent arrivals are reversed from those of the direct p waves as predicted by the theory of fault zone head waves for slip on the san andreas fault the presence of fault zone head waves in local seismic network data may help account for scatter in earthquake locations and source mechanisms the fault zone head waves indicate that the velocity contrast across the san andreas fault near parkfield is approximately 4 percent further studies of these waves may provide a way of assessing changes in the physical state of the fault system

mid mantle scatterers near the mariana slab detected with a double array method we use a cluster of deep earthquakes the fore and aftershocks of the 23 aug 1995 mw 7 1 18 8n 145 3e h 595 km event in the mariana subduction zone as source array to locate where waves scatter near the deep slab in order to obtain the high precision location needed in this context we first relocate the events with a modified master event technique using the double beam method on the relocated events and data from the warramunga array in australia we identified two non standard s to p conversions arriving about 20 5 and 24 s after the p wave the corresponding scatterers are approximately located at a depth of 790 km 720 km and a distance of 0 9 to the southeast 2 3 to the southwest of the main shock the scatterers positions correspond to the location of lithosphere subducted below the 660 km discontinuity

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

inversion of gps data for spatially variable slip rate on the san andreas fault near parkfield ca we analyze gps data collected from 1991 1998 at 35 sites near the parkeld segment of the san andreas fault inverting the resultant site velocities for the distri bution of interseismic slip rate on the san andreas reveals an area of low slip rate on thefault extendingfrom between middle mountain and carr hill to southeast of gold hill this slip rate patternis similar to thatfoundbyharris and segall 1987 using trilateration data collected between 1966 and 1984 we infer a deep slip rate 33 mm yr and depth of the transition between seismogenic and non seismogenic slip 14km thatagree betterwithindependentgeologic ev idence than those found in the 1987 study in contrast to harris and segall 1987 wendnoevidenceoffault normal contraction

nonvolcanic tremor evolution and the san simeon and parkfield california earthquakes nonvolcanic tremors occur adjacent to locked faults and may be closely related to the generation of earthquakes monitoring of the san andreas fault in the parkfield california region revealed that after two strong earthquakes tremor activity increased in a nearly dormant tremor zone increased and became periodic in a previously active zone and has remained elevated and periodic for over 4 years static shear and coulomb stress increases of 6 to 14 kilopascals from these two earthquakes are coincident with sudden increases in tremor rates the persistent changes in tremor suggest that stress is now accumulating more rapidly beneath this part of the san andreas fault which ruptured in the moment magnitude 7 8 ft tejon earthquake of 1857

slowness corrections one way to improve idc products the first step to identify and locate a seismic event is the association of observed onsets with common seismic sources this is especially important in the context of monitoring the comprehensive nuclear test ban treaty ctbt at the international data center idc being developed in vienna austria well defined slowness measurements are very useful for associating seismic phases to presumed seismic events shortly after installation of the first seismic arrays systematic discrepancies between measured and theoretically predicted slowness values were observed and therefore slowness measurements of seismic stations should be calibrated the observed slownesses measured with small aperture arrays some of which will be included in the international monitoring system ims now being implemented for verifying compliance with the ctbt show large scatter and deviations from theoretically expected values however in this study a method is presented by which mean slowness corrections can be derived which show relatively stable patterns specific to each array the correction of measured slowness values of these arrays clearly improved the single array location capabilities applying slowness corrections with seismic phases observed by arces fines geres and nores and associated to seismic events in the bulletins of the prototype international data center pidc in arlington va also clearly demonstrates the advantages of these corrections for arrays with large slowness deviations that are due to the influence of a dipping layer the corrections were modeled with a sine function depending on the measured azimuth in addition the measured values can be weighted with the corresponding uncertainties known from the process of deriving the mean corrections

evidence for normal and inhomogeneous lowermost mantle and core mantle boundary structure under the arctic and northern canada summary seismic p waves from a total of about 200 nuclear explosions in the usa the former ussr and china observed at 10 arrays and four networks in europe canada and the usa are used to analyse the structure at the base of the mantle and the core mantle boundary cmb the simple waveforms and well controlled source parameters of nuclear explosions allow one to use the events as source arrays in addition to the usual receiver array configuration a new array technique double beamforming kruger et al 1993 integrating both concepts is applied which increases the slowness resolution considerably a total of 56 source receiver combinations i e reflection points in the lower mantle or on the cmb could be analysed in five regions anomalous arrivals pdp with slowness and arrival times between those of p and pcp are observed one of these five areas svalbard region shows short period pcp p amplitude ratios which are about three times higher than those predicted by standard earth models in the severnaya zemlya region where pdp and pcp precursors were observed previously kruger et al 1993 pcp shows azimuth deviations of up to 10 for some other regions deviations of the pcp waveform from the direct p waveform are also observed these anomalous phases and the pcp waveform distortions cannot be explained with standard 1 d earth models they are probably produced by inhomogeneities in the lowermost mantle the observed variations in the waveforms are strong indications of a laterally heterogeneous structure in two depth ranges the first is the cmb and its immediate vicinity of a few tens of kilometres the second region is the depth range between about 200 and 300 km above the cmb maps of the north pole region giving the distributions of inhomogeneities in the lower mantle and on the cmb are presented these maps show evidence of strong heterogeneity of the d boundary layer and possibly also of the cmb in the same area

tracking the rupture of the mw 9 3 sumatra earthquake over 1 150 km at teleseismic distance on 26 december 2004 a moment magnitude mw 9 3 earthquake occurred along northern sumatra the nicobar and andaman islands resulting in a devastating tsunami in the indian ocean region the rapid and accurate estimation of the rupture length and direction of such tsunami generating earthquakes is crucial for constraining both tsunami wave height models as well as the seismic moment of the events compressional seismic waves generated at the hypocentre of the sumatra earthquake arrived after about 12 min at the broadband seismic stations of the german regional seismic network grsn located approximately 9 000 km from the event here we present a modification of a standard array seismological approach and show that it is possible to track the propagating rupture front of the sumatra earthquake over a total rupture length of 1 150 km we estimate the average rupture speed to be 2 3 2 7 km s 1 and the total duration of rupture to be at least 430 s and probably between 480 and 500 s

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

imaging the dead sea transform with scattered seismic waves summary with controlled seismic sources and specifically designed receiver arrays we image a subvertical boundary between two lithological blocks at the arava fault af in the middle east the af is the main strike slip fault of the dead sea transform dst in the segment between the dead sea and the red sea our imaging migration method is based on array beamforming and coherence analysis of p to p scattered seismic phases we use a 1 d background velocity model and the direct p arrival as a reference phase careful resolution testing is necessary because the target volume is irregularly sampled by rays a spread function describing energy dispersion at localized point scatterers and synthetic calculations for large planar structures provides estimates of the resolution of the images we resolve a 7 km long steeply dipping reflector offset roughly 1 km from the surface trace of the af the reflector can be imaged from about 1 km down to 4 km depth previous and ongoing studies in this region have shown a strong contrast across the fault low seismic velocities and electrical resistivities to the west and high velocities and resistivities to the east of it we therefore suggest that the imaged reflector marks the contrast between young sedimentary fill in the west and precambrian rocks in the east if correct the boundary between the two blocks is offset about 1 km east of the current surface trace of the af

testing small aperture array analysis on well located earthquakes and application to the location of deep tremor we have here analyzed local and regional earthquakes using array tech niques with the double aim of quantifying the errors associated with the estimation of propagation parameters of seismic signals and testing the suitability of a probabilistic location method for the analysis of nonimpulsive signals we have applied the zero lag cross correlation method to earthquakes recorded by three dense arrays in puget sound and vancouver island to estimate the slowness and back azimuth of direct p waves and s waves the results are compared with the slowness and back azimuth computed from the source location obtained by the analysis of data recorded by the pacific northwest seismic network pnsn this comparison has allowed a quanti fication of the errors associated with the estimation of slowness and back azimuth obtained through the analysis of array data the statistical analysis gives bp 10 and bs 8 as standard deviations for the back azimuth and sp 0 021 sec km and ss 0 033 sec km for the slowness results of the p and s phases respec tively these values are consistent with the theoretical relationship between slowness and back azimuth and their uncertainties we have tested a probabilistic source location method on the local earthquakes based on the use of the slowness estimated for two or three arrays without taking into account travel time information then we applied the probabilistic method to the deep nonvolcanic tremor recorded by the arrays during july 2004 the results of the tremor location using the probabilistic method are in good agreement with those obtained by other techniques thewide depth range of between 10 and 70 km and the source migration with time are evident in our results the method is useful for locating the source of signals characterized by the absence of pickable seismic phases

detecting deep tectonic tremor in taiwan with a dense array abstract we perform a systematic detection of deep tectonic tremor beneath the southern central range in taiwan using a dense small aperture seismic array deployed in february 2011 the array has been recording tectonic tremor nearly continuously for 134 days including tremor triggered by the 2011 m w 9 0 tohoku oki earthquake we use broadband frequency wavenumber beamforming and moving window grid search methods to compute array parameters for all continuous data and identify tremor as coherent nonimpulsive seismic signals with deep incidence angles the obtained array parameters closely match with those of relocated local earthquakes and triggered tremor bursts located by the waveform envelope correlation and clustering wecc method indicating the robustness of our array technique during the 134 day study period we detect tremor for 44 days with a total duration of 1481 min three to six times as long as the detection of tremor by the wecc method we find a relative quiescence in ambient tremor activity for about 20 days following the 2011 tohoku oki earthquake suggesting that dynamic stresses from the distant mainshock triggered most tremor close to failure resulting in a temporary lack of tremor activity in some cases we observe rapid tremor migration with a speed at the order of 40 50 km hr that is similar to the speed of fast tremor migration along dip on narrow streaks in japan and cascadia our results suggest that dense array techniques are capable of capturing detailed spatiotemporal evolutions of tremor behaviors in southern taiwan online material tables of station coordinates and tremor event parameters and figures of the moving window grid search test with local earthquakes tremor triggered by the 2011 tohoku oki earthquake and additional examples of detected ambient tremors

apparent vertical moho offsets under continental strike slip faults from lithology contrasts in the seismogenic crust we demonstrate that observed contrasts of upper crustal structures across large continental strike slip faults are sufficient to produce artificial vertical moho offsets of several kilometers in studies using laterally homogenous models this can have significant impact on efforts to understand how the observed surface displacement is accommodated in the deep crust an existing hypothesis that continental strike slip faults extend as discrete narrow features through the entire crust rests partly on inferred vertical moho offsets across the faults based on teleseismic converted wave receiver function studies however such studies typically do not account for the juxtaposition of different structures across the faults which can lead to significant e g 10 contrasts of seismic velocities in the upper crust observed profiles of velocity contrasts across faults can bias images of the deep structure to the extent where a large 5 km moho offset can be purely apparent rather than real constraining the existence and size of true vertical moho offsets below continental strike slip faults thus require calculations that account for the across fault lithology contrasts accurate results on the geometry of moho across faults can have important implications for lithospheric deformation crustal tomography strain localization and partitioning in the crust continental rheology and geodynamics

evidence for postseismic deformation of the lower crust following the 2004 mw6 0 parkfield earthquake previous studies have shown that postseismic relaxation following the 2004 mw6 0 parkfield ca earthquake is dominated by afterslip however we show that some fraction of the afterslip inferred from kinematic inversion to have occurred immediately below the seismically ruptured area may in fact be a substitute for viscous postseismic deformation of the lower crust using continuous gps and synthetic aperture radar interferometry we estimate the relative contribution of shallow afterslip at depth less than 20km and deeper seated deformation required to account for observed postseismic surface displacements exploiting the possible separation in space and time of the time series of displacements predicted from viscoelastic relaxation we devise a linear inversion scheme that allows inverting jointly for the contribution of afterslip and viscoelastic flow as a function of time we find that a wide range of models involving variable amounts of viscoelastic deformation can fit the observations equally well provided that they allow some fraction of deep seated deformation at depth larger than 20 km these models require that the moment released by postseismic relaxation over 5 years following the earthquake reached nearly as much as 200 of the coseismic moment all the models show a remarkable complementarity of coseismic and shallow afterslip distributions some significant deformation at lower crustal depth 20 26 km is required to fit the geodetic data the condition that postseismic deformation cannot exceed complete relaxation places a constraint on the amount of deep seated deformation the analysis requires an effective viscosity of at least 10 18 pa s of the lower crust assuming a semi infinite homogeneous viscous domain this deep seated deformation is consistent with the depth range of tremors which also show a transient postseismic response and could explain as much as 50 of the total postseismic geodetic moment the remaining fraction being due to afterslip at depth shallower than 20 km lower crustal postseismic deformation could reflect a combination of localized ductile deformation and aseismic frictional sliding

distribution and fractionation of rare earth elements and yttrium in suspended and bottom sediments of the kali estuary western india concentrations of rare earth elements ree and yttrium y and major metals al fe and mn were measured in suspended particulate matter spm and bottom sediments of the kali estuary western india for their distribution and fractionation the contents of spm and metals in it were more uniform along the longitudinal transect during the monsoon during the post and pre monsoons low spm in the upper middle estuary coincided with high fe and mn and total ree ree but in the lower estuary spm and its ree content increased seaward while fe and mn decreased the y ho ratios decreased seaward during the monsoon but increased during the post monsoon sm nd ratios were more uniform along the transect during monsoon but decreased marginally seaward in other seasons the post archean average australian shale paas normalized ree patterns exhibited middle ree and heavy ree enrichment with positive ce text ce text ce eu text eu text eu and y anomalies the text ce text ce increased but text eu text eu decreased marginally seaward the fine grained sediments showed higher ree and lower y ho ratios than in coarse grained sediments the paas normalized ree patterns of sediment were similar to that of spm the results revealed two processes colloidal flocculation and coagulation of metals in the low salinity zone and an estuarine turbidity maximum in the high salinity zone rare earths and yttrium rey in spm and sediments primarily reflected the source rock composition than that of chemical weathering apart from physico chemical processes the mineralogy and grain size of sediments controlled the distribution and fractionation of rey in the estuary

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