topographically controlled fronts in the ocean and their biological influence headlands islands and reefs generate complex three dimensional secondary flows that result in physical and biological fronts mixing and diffusion processes near these reefs and headlands are quite different from these processes in the open sea and classical advection diffusion models that were developed for the open sea are not valid near shore topographically generated fronts affect the distribution of sediments and they aggregate waterborne eggs larvae and plankton this aggregation influences the distribution and density of benthic assemblages and of pelagic secondary and tertiary predators

seasonal variations of observed noise amplitudes at 2 18 hz in southern california we show that noise amplitudes at frequencies above 1 hz exhibit strong seasonal variations in a broad southern california region the results are based on 3 component seismic data recorded between 2002 and 2009 by 30 stations focusing on continuous 6 hr night time segments the seismograms are bandpass filtered in nine frequency bands between 2 and 18 hz squared amplitudes are median filtered to reduce the influence of earthquake signals and integrated to yield half hourly noise energy estimates the 6 hr minimum energy values are converted back to ground velocity and used as representative daily noise level amplitudes notwithstanding various trends drifts and other transient complexities a common feature of the resulting time series in both the horizontal and vertical components are annual amplitude changes at all examined frequencies and all stations the strength of amplitude variations shows no correlation with distance from the coast and some particularly clear seasonal changes are seen near topographic features in arid uninhabited areas comparison to meteorological data suggests that the main sources for the high frequency noise field are variations of temperature and wind at the surface in addition to acting directly on topographic irregularities and other surface features these sources and especially temperature changes may also generate high frequency noise by inducing multitudinous small scale failures in the shallow crust

spurious velocity changes caused by temporal variations in ambient noise frequency content ambient seismic noise cross correlations are now being used to detect temporal variations of seismic velocity which are typically on the order of 0 1 per cent at this small level temporal variations in the properties of noise sources can cause apparent velocity changes for example the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms here we show that if the stretching method is used to measure time shifts then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching with realistic seasonal variations of frequency content in the los angeles basin our numerical tests produce about 0 05 per cent apparent velocity change comparable to what meier et al observed in the los angeles basin we find that the apparent velocity change from waveform stretching depends on time windows and station pair distances and hence it is important to test a range of these parameters to diagnose the stretching bias better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring

coherence of seismic body waves from local events as measured by a small aperture array eight local earthquakes were recorded during the operation of a small aperture seismic array at pinyon flat california the site was chosen for its homogeneous granitic geology and its planar topography amplitude spectral ratios for the same signal measured at different stations had average values of less than 2 and maximum values of 7 magnitude squared coherences were estimated for all station pairs these estimates were highest for the p wave arrivals on the vertical component and lowest for the p wave recorded on the transverse component at 500 m station separation the p and s waves were incoherent above 15 hz and 10 hz respectively coherence for both the p and s waves decrease as frequency increases and as distance increases the coherence of signals from borehole sensors located at 300 and 150 m depth displays higher average coherence than equally spaced sites located on the surface the results here suggest that even for sites that appear to be very similar that is those which are located on a planar surface within a few meters of granite bedrock the measured seismic wavefield can be distorted substantially over scale lengths of 500 m coherence properties were calculated from synthetic seismograms which were computed for velocity models with exponential and self similar distribution perturbations standard deviations of 10 are not sufficient for the random velocity distributions to approximate the results from the small aperture array

detecting seasonal variations in seismic velocities within los angeles basin from correlations of ambient seismic noise summary we analyse 3 yr of continuous seismic records from broad band stations of the caltech regional seismic network ci in vicinity of the los angeles basin using correlations of ambient seismic noise relative velocity variations in the order of 0 1 per cent can be measured between all interstation pairs it is the first time that such an extensive study between 861 interstation pairs over such a large area has been carried out we perform these measurements using the stretching technique assuming that one of the two waveforms is merely a stretched version of the other obviously this assumption is always violated and the two waveforms are generally decorrelated due to temporal changes in the earth crust due to different sources or simply because the cross correlations are not fully converged we investigate the stability of these measurements by repeating each measurement over various time windows of equal length on average between all interstation pairs in the los angeles basin a seasonal signal in the relative velocity variation is observed with peaks and troughs during winter and summer time respectively generally the observed signal decreases with increasing interstation distance and relative traveltime perturbations can only be measured up to an interstation distance of 60 km furthermore the traveltime perturbations do not depend on azimuth of station pairs suggesting that they are not related to seasonal variations of the noise sources performing a simple regionalization by laterally averaging measurements over a subset of stations we found the sedimentary basin showing the most consistent signal and conclude that the observed seasonality might be induced either by changes in the ground water aquifer or thermo elastic strain variations that persist down to a depth of 15 22 km

nonlinearity in rock evidence from earth tides the earth is sinusoidally stressed by tidal forces if the stress strain relation for rock is nonlinear energy should appear in an earth tide record at frequencies which are multiples of those of the larger tidal lines an examination of the signals to be expected for different nonlinear deformation laws shows that for a nonlinear response without dissipation the largest anomalous signal should occur at twice the forcing frequency whereas for nonlinear laws involving dissipation cusped hysteresis loops the anomalous signal will be greatest at 3 times this frequency the size of the signal in the dissipative case depends on the amount by which dissipation affects the particular response being measured for measurements of strain tides this depends on whether dissipation is assumed to be present throughout the earth or localized around the point of measurement an analysis of 5 7 years of strain tide records from pinon flat california shows a small signal at twice the frequency of the largest m2 tide most of the observed signal can be explained by loading from nonlinear water tides in the gulf of california and the pacific ocean the residual nonlinear tide is 65 db less than the m2 tide the signal at 3 times the m2 frequency is compatible with a linear model or with nonlinear hysteresis loops provided that nonlinear dissipation occurs throughout the earth nonlinear dissipation in the rocks near the strainmeter would produce a larger signal than is seen

stable and unstable damage evolution in rocks with implications to fracturing of granite summary we address the relation between the rock rigidity and crack density by comparing predictions of a viscoelastic damage rheology model to laboratory data that include direct microscopic mapping of cracks the damage rheology provides a generalization of hookean elasticity to a non linear continuum mechanics framework incorporating degradation and recovery of the effective elastic properties transition from stable to unstable fracturing and gradual accumulation of irreversible deformation this approach is based on the assumption that the density of microcracks is uniform over a length scale much larger than the length of a typical crack yet much smaller than the size of the entire deforming domain for a system with a sufficiently large number of cracks one can define a representative volume in which the crack density is uniform and introduce an intensive damage variable for this volume we tested our viscoelastic damage rheology against sets of laboratory experiments done on mount scott granite based on fitting the entire stress strain records the damage variable is constrained and found to be a linear function of the crack density an advantage of these sets experiments is that they were preformed with different loading paths and explicitly demonstrated the existence of stable and unstable fracturing regimes we demonstrate that the viscoelastic damage rheology provides an adequate quantitative description of the brittle rock deformation and simulates both the stable and unstable damage evolution under various loading conditions comparison between the presented data analysis of experiments with mount scott granite and previous results with westerly granite and berea sandstone indicates that granular or porous rocks have lower seismic coupling this implies that the portion of elastic strain released during a seismic cycle as brittle deformation depends on the lithology of the region hence upper crustal regions with thick sedimentary cover or fault zones with high degree of damage are expected to undergo a more significant inelastic deformation in the interseismic period compared to intact crystalline rocks

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

near surface scattering effects observed with a high frequency phased array at pinyon flats california analysis of data collected by a high frequency array experiment con ducted at pinyon flat in southern california provides strong evidence that the high frequency wave field from local earthquakes at this hard rock site are strongly dis totted by near surface scattering the seismic array we deployed consisted of 60 2 hz natural frequency three component sensors deployed in a three dimensional array two of the sensors were located in boreholes at 150 and 275 m depth the other 58 sensors were deployed in an areal array above these boreholes thirty six of these were deployed in a 6 by 6 element grid array with a nominal spacing of 7 m centered over the borehole sensors the remaining 22 seismometers were laid out in two 11 element linear arrays radiating outward from the grid coherence calculations reveal a rapid loss of coherence at frequencies over 15 hz at all but the shortest length scales of this array three dimensional visualization techniques were used to closely examine the spatial stability of particle motions of p and s waves this reveals systematic variations of particle motion across the array in which the particle motion tracks tilt drastically away from the backazimuth expected for an isotropic medium these variations however are frequency dependent below around 8 hz the particle motions become virtually identical for all stations at progressively higher frequen cies the wave field particle motion becomes increasingly chaotic frequency wave number analysis of these data provide quantitative measures of the same phenomena we find that direct wave f k spectra are bathed in a background of signal generated noise that varies from 10 to 30 db down from the direct arrival signal this signal generated noise appears to be nearly white in wavenumber indicating the wavelength of this noise on the scale of tens of meters and less refraction measurements we made on two lines crisscrossing the array reveal that the weathered layer velocities are highly variable and define a very strong wave guide measured surface p wave velocities varied from 400 to 1300 rn sec and velocities at depth of approximately 15 m varied from 1600 to 2700 m sec previous measurements in the boreholes showed that the intact granite below about 65 m depth has a velocity of approximately 5400 m sec these results demonstrate the extreme velocity contrast and degree of velocity heterogeneity of the near surface at this site we conclude that all the ob servations we made can be explained by strong scattering of incident body wave signals into a complex mishmash of body wave and surface wave modes in this heterogeneous near surface wave guide

tidal modulation of seismic noise and volcanic tremor 1 we present seismic data from fogo volcano cape verde republic that document a tidal control on the amplitude of seismic noise and volcanic tremor the effect is detectable in the raw data by simple eye inspection we identified the main periodicity in the noise modulation which coincides with the tidal component m2 the signal duration of 40 days together with a sampling rate of 1440 samples per day seismic r m s time series allowed the resolution of m2 from the neighbor solar frequencies that are often related to environmental effects spectral analysis shows that the modulation affects selectively the frequency range 2 0 hz 3 0 hz which we interpret as volcanic tremor white noise from 1 5 hz to 7 hz is also modulated comparison with meteorological data reinforces the conclusion that the effect is not due to environmental parameters

in situ observations of velocity changes in response to tidal deformation from analysis of the high frequency ambient wavefield we report systematic seismic velocity variations in response to tidal deformation measurements are made on correlation functions of the ambient seismic wavefield at 2 8 hz recorded by a dense array at the site of the pinon flat observatory southern california the key observation is the dependence of the response on the component of wave motion and coda lapse time measurements on the vertical correlation component indicate reduced wave speeds during periods of volumetric compression whereas data from horizontal components show the opposite behavior compatible with previous observations these effects are amplified by the directional sensitivities of the different surface wave types constituting the early coda of vertical and horizontal correlation components to the anisotropic behavior of the compliant layer the decrease of the velocity volumetric strain sensitivity s with indicates that this response is constrained to shallow depths the observed velocity dependence on strain implies nonlinear behavior but conclusions regarding elasticity are more ambiguous the anisotropic response is possibly associated with inelastic dilatancy of the unconsolidated low velocity material above the granitic basement however equal polarity of vertical component velocity changes and deformation in the vertical direction indicate that a nonlinear poisson effect is similarly compatible with the observed response pattern peak relative velocity changes at small are 0 03 which translates into an absolute velocity strain sensitivity of s 5 10 3 and a stress sensitivity of 0 5 mpa 1 the potentially evolving velocity strain sensitivity of crustal and fault zone materials can be studied with the method introduced here

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

seismic velocity change patterns along the san jacinto fault zone following the 2010 m7 2 el mayor cucapah and m5 4 collins valley earthquakes

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

ultrasonic velocities acoustic emission characteristics and crack damage of basalt and granite acoustic emissions ae compressional p shear s wave velocities and volumetric strain of etna basalt and aue granite were measured simultaneously during triaxial compression tests deformation induced ae activity and velocity changes were monitored using twelve p wave sensors and eight orthogonally polarized s wave piezoelectric sensors volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface p wave velocity in basalt is about 3 km s at atmospheric pressure but increases by 50 when the hydrostatic pressure is increased to 120 mpa in granite samples initial p wave velocity is 5 km s and increases with pressure by 20 the pressure induced changes of elastic wave speed indicate dominantly compliant low aspect ratio pores in both materials in addition etna basalt also contains high aspect ratio voids in triaxial loading stress induced anisotropy of p wave velocities was significantly higher for basalt than for granite with vertical velocity components being faster than horizontal velocities however with increasing axial load horizontal velocities show a small increase for basalt but a significant decrease for granite using first motion polarity we determined ae source types generated during triaxial loading of the samples with increasing differential stress ae activity in granite and basalt increased with a significant contribution of tensile events close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly a concomitant increase of double couple events indicating shear suggests shear cracks linking previously formed tensile cracks

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

pulse of the seafloor tidal triggering of microearthquakes at 9 50 n east pacific rise 1 unequivocal evidence of tidal triggering is observed for microearthquakes 0 4 to 2 0 ml recorded between october 2003 to april 2004 near 9 50 n on the east pacific rise epr although semidiurnal tidal stress changes are small 99 9 nonrandom temporal distribution with events occurring preferentially near times of peak extension due to the proximity of this site to an ocean tidal node where changes in sea surface height are minimal periodic stress changes are dominated by the solid earth tide in contrast previous studies on the juan de fuca ridge have shown microearthquake triggering to be a response to seafloor unloading during times of low ocean tide the modulation of 9 50 n microearthquakes by small amplitude periodic stresses is consistent with earthquake nucleation within a high stressing rate environment that is maintained near a critical state of failure by on axis magmatic and hydrothermal processes

seismic evidence of nonlinear crustal deformation during a large slow slip event in mexico repeated cross correlations of ambient seismic noise indicate a long term seismic velocity change associated with the 2006 m7 5 slow slip event sse in the guerrero region mexico because the sse does not radiate seismic waves the measured velocity change cannot be associated with the response of superficial soil layers to strong shaking as observed for regular earthquakes the perturbation observed maximized at periods between 7 s and 17 s which correspond to surface waves with sensitivity to the upper and middle crust the amplitude of the relative velocity change 10 3 was much larger than the volumetric deformation 10 6 at the depths probed 5 20 km moreover the time dependence of the velocity perturbation indicated that it was related to the strain rate rather than the strain itself this suggests that during strong slow slip events the deformation of the overlying crust shows significant nonlinear elastic behavior

time lapse monitoring of rock properties with coda wave interferometry 1 the coda of seismic waves consists of that part of the signal after the directly arriving phases in a finite medium or in one that is strongly heterogeneous the coda is dominated by waves which have repeatedly sampled the medium small changes in a medium which may have no detectable influence on the first arrivals are amplified by this repeated sampling and may thus be detectable in the coda we refer to this use of multiple sampling coda waveforms as coda wave interferometry we have exploited ultrasonic coda waves to monitor time varying rock properties in a laboratory environment we have studied the dependence of velocity on uniaxial stress in berea sandstone the temperature dependence of velocity in granite and in aluminum and the change in velocity due to an increase of water saturation in sandstone there are many other possible applications of coda wave interferometry in geophysics including dam and volcano monitoring time lapse reservoir characterization earthquake relocation and stress monitoring in mining and rock physics

near surface velocities and attenuation at two boreholes near anza california from logging data to investigate near surface site effects in granite rock we drilled 300 m deep boreholes at two sites which are collocated with stations from the digital array at anza california the first borehole was sited at station knw keenwild fire station which is located along a ridge line about 8 7 km east of the san jacinto fault zone station pfo pinon flat observatory chosen for the second site is another 6 km further to the east of station knw and is located on a gently sloping hillside we logged each borehole for p and s wave velocities as well as for crack density and orientation p waves were generated by striking a plate with a hammer at the surface a tool consisting of weighted anvils driven by compressed air against end plates along a 3 5 m beam was used to generate shear waves signals were recorded downhole with a three component sensor package at 2 5 m intervals from the surface to 50 m depth and at 5 m intervals from 50 m depth to the bottom of the hole velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth travel times were computed for the first breaks at shallow depths however below about 100 m depth times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable the knw site yielded a shear velocity of 1 9 km sec by only 30 m in depth and reached close to 2 6 km sec at the bottom of the hole p wave velocities at knw were also high at 5 4 km sec starting at 120 m depth the pfo site had similar but slightly higher shear wave velocities the bottom hole shear wave velocity reached 3 0 km sec and the p wave velocity was 5 4 km sec shear wave attenuation was computed using both the pulse rise time and spectral ratio methods at station knw attenuation was significant only in an interval between 17 5 and approximately 40 m in depth over the top 50 m attenuation corresponding to a q of about 8 was obtained a total t of 0 004 sec was measured for this interval pulse rise times also increased rapidly in this zone the spectral ratio data for station pfo yields two peaks in attenuation above 50 m similar to the attenuation found for station knw the peak in attenuation corresponds to a q of about 11 averaged over the top 50 m spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 hz significant motion perpendicular to the polarizations of the first shear wave arrival was recorded within a few meters of the surface apparently the rock structure is sufficiently complicated that body waves are being converted sh to sv at oblique incidence very close to the surface the presence of these elliptical particle motions within a mere few m of the pure shear wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not by itself a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth s crust crack densities and orientations were determined from televiewer records these records showed cracks with a preferred direction at station knw and of a greater density than at station pfo at station pfo crack densities were smaller and more diffuse in orientation

tomographic investigation of the wear along the san jacinto fault southern california the seismic properties of the wear along the san jacinto fault are investigated using local seismic records for clustered fault zone earthquakes spatial reciprocity allows us to use the seismicity along fault plane to mimic the situation where receiver arrays are placed at depth on the fault plane a seismic record at the event location is constructed by stacking the original station records waveform cross correlations is then used to calculate the traveltimes of shear waves traveling between the pair of events we analyze 157 small earthquakes occurring between 1998 and 2004 on the san jacinto and elsinore fault zones low shear velocities in the san jacinto fault zone related to wear and gouge are persistently observed up to the depth of brittle ductile transition zone 16 km on the other hand low velocities in the elsinore fault zone are only visible in the northwestern portion at shallow depth the wear structures in the san jacinto fault zone display lower shear velocities by 6 8 than those of the wall rock 2005 elsevier b v all rights reserved

seismic wave velocity changes and stress build up in the crust of the kanto tokai region we show there are large temporal p wave velocity changes in the crust of the kanto tokai region in japan from repeated observations of explosions we find that the variation is the response of the crustal rocks to two components of stress change the tidal stress and the secular stress accumulation the inferred annual rate of fractional velocity change year caused by the stress accumulation in the upper crust is of the order of 10 3 year the results indicate that the build up of stress in the crust can be monitored by precise observations of seismic wave velocities

anatomy of the high frequency ambient seismic wave field at the tcdp borehole 1 the taiwan chelungpu fault drilling project tcdp installed a vertical seismic array between 950 and 1270 m depth in an active thrust fault environment in this paper we analyze continuous noise records of the tcdp array between 1 and 16 hz we apply multiple array processing and noise correlation techniques to study the noise source process properties of the propagation medium and the ambient seismic wave field diurnal amplitude and slowness patterns suggest that noise is generated by cultural activity the vicinity of the recording site to the excitation region indicated by a narrow azimuthal distribution of propagation directions leads to a predominant ballistic propagation regime this is evident from the compatibility of the data with an incident plane wave model polarized direct arrivals of noise correlation functions and the asymmetric arrival shape evidence for contributions from scattering comes from equilibrated earthquake coda energy ratios the frequency dependent randomization of propagation directions and the existence of correlation coda waves we conclude that the ballistic and scattered propagation regime coexist where the first regime dominates the records but the second is weaker yet not negligible consequently the wave field is not equipartitioned correlation signal to noise ratios indicate a frequency dependent noise intensity iterations of the correlation procedure enhance the signature of the scattered regime discrepancies between phase velocities estimated from correlation functions and in situ measurements are associated with the array geometry and its relative orientation to the predominant energy flux the stability of correlation functions suggests their applicability in future monitoring efforts

feasibility of borehole ambient noise interferometry for permanent reservoir monitoring the analysis of seismic ambient noise acquired during temporary or permanent microseismic monitoring campaigns e g improved enhanced oil recovery monitoring surveillance of induced seismicity is potentially well suited for time lapse studies based on seismic interferometry no additional data acquisition required ambient noise processing can be automatized to a high degree and seismic interferometry is very sensitive to small medium changes thus there is an opportunity for detection and monitoring of velocity variations in a reservoir at negligible additional cost and effort data and results are presented from an ambient noise interferometry study applied to two wells in a producing oil field in romania borehole microseismic monitoring on three component geophones was performed for four weeks concurrent with a water flooding phase for improved oil recovery from a reservoir in ca 1 km depth both low frequency 2 hz 50 hz p and s waves propagating through the vertical borehole arrays were reconstructed from ambient noise by the virtual source method the obtained interferograms clearly indicate an origin of the ambient seismic energy from above the arrays thus suggesting surface activities as sources it is shown that ambient noise from time periods as short as 30 seconds is sufficient to obtain robust interferograms sonic log data confirm that the vertical and horizontal components comprise first arrivals of p wave and s waves respectively the consistency and high quality of the interferograms throughout the entire observation period further indicate that the high frequency part up to 100 hz represents the scattered wave field the temporal variation of apparent velocities based on first arrival times partly correlates with the water injection rate and occurrence of microseismic events it is concluded that borehole ambient noise interferometry in production settings is a potentially useful method for permanent reservoir monitoring due to its high sensitivity and robustness

memory relaxation and microfracturing in dilatant rock when palisades diabase and westerly granite are made dilatant by cyclic differential stress not exceeding 85 of fracture strength they behave as nonelastic energy absorbing media however in some ways their properties show reversibility more typical of elastic media the quasi elastic behavior is characterized by the property memory memory in dilatant rock is manifested by the closure of material property hysteresis loops when the sample is returned to certain previous differential stress states simple examples of memory have been observed before in westerly granite the present work confirms the existence of memory for strain and compressional wave velocity in westerly granite and palisades diabase at confining pressures between 250 and 1500 bars memory of maxima or minima of the stress difference can be developed with multiple points remembered simultaneously a theory of memory based on reversible tensile griffith cracks was developed which predicts a variety of phenomena many of which have been observed a property that is not predicted is the healing which occurs when unloading is stopped and the load is held constant a time dependent increase in velocity and decrease in sample volume is observed consistent with the healing of cracks relaxation ceases after approximately 2 min after relaxation a further decrease in load produces an initial elastic response followed by a return to the previous nonelastic behavior perfect memory is lost when microfracturing occurs as a result of either exceeding the previous absolute maximum stress or extensive cycling acoustic emissions are observed for conditions where memory is not perfect and are not observed when memory is perfect using travel time data a new low value was found for the dependence of dilatancy onset on pressure

seismic velocity variations at tcdp are controlled by mjo driven precipitation pattern and high fluid discharge properties using seismic noise based monitoring techniques we find that seismic velocity variations dv v observed with the borehole array of the taiwan chelungpu fault drilling project tcdp are controlled by strong precipitation events associated with the madden julian oscillation mjo a dynamic intraseasonal atmospheric pattern in the tropical atmosphere high frequency noise 1 hz excited by steady anthropogenic activity in the vicinity of the tcdp allows daily resolution of dv v time series relatively large fluid discharge properties control the equilibration of the ground water table and hence seismic velocities on time scales smaller than the average precipitation recurrence interval this leads to the observed synchronous 50 80 day periodicity in dv v and rainfall records in addition to the dominant annual component further evidence for the governing role of hydraulic properties is inferred from the similarity of observed dv v timing amplitude and recovery properties with dv v synthetics generated by a combined model of ground water table changes and diffusive propagation of seismic energy the lapse time dependent increase of dv v amplitudes is controlled by the sensitivity of the diffuse wave field sampled at 1100 m depth to shallower water level fluctuations the significant vertical offset between stations and water level explains the direct dependence which is opposite to the trend previously inferred from measurements at the surface

long term observation of in situ seismic velocity and attenuation 1 we conducted 1 year continuous measurements of in situ compressional wave velocity and attenuation across a distance of 12 m in a vault at the coast of miura bay japan using a piezoelectric transducer as the ultrasonic wave source we detected for the first time periodic variations in both velocity and attenuation with amplitudes of 0 3 and of 4 respectively corresponding to the diurnal and semidiurnal lunar and solar tides these variations correlate well with the in situ areal strain change due to tidal ocean loading estimated from the strain records about 100 m away from the observational site relative minimum velocity and relative maximum attenuation occur at every time of relative maximum areal strain expansion suggesting that opening closure of pores or cracks of in situ rocks is responsible for these periodic variations the velocity variation shows a remarkable 14 day periodicity corresponding to the spring and neap tides arising from a nonlinear response of the velocity change to tidal strain change such that the velocity change depends on how slowly the tidal dilatation departs from its peak value

induced dynamic nonlinear ground response at garner valley california we present results from a prototype experiment in which we actively induce observe and quantify in situ nonlinear sediment response in the near surface this experiment was part of a suite of experiments conducted during august 2004 in garner valley california using a large mobile shaker truck from the network for earthquake engineering simulation nees facility we deployed a dense accel erometer array within meters of the mobile shaker truck to replicate a controlled laboratory style soil dynamics experiment in order to observe wave amplitude dependent sediment properties ground motion exceeding 1g acceleration was pro duced near the shaker truck thewave field was dominated by rayleigh surface waves and ground motions were strong enough to produce observable nonlinear changes in wave velocity we found that as the force load of the shaker increased the rayleigh wave phase velocity decreased by as much as 30 at the highest frequencies used up to 30 hz phase velocity dispersion curves were inverted for s wave velocity as a function of depth using a simple isotropic elastic model to estimate the depth depen dence of changes to the velocity structure the greatest change in velocity occurred nearest the surface within the upper 4 m these estimated s wave velocity values were used with estimates of surface strain to compare with laboratory based shear modulus reduction measurements from the same site our results suggest that it may be possible to characterize nonlinear soil properties in situ using a noninvasive field technique

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

seismic tomography of the southern california plate boundary region from noise based rayleigh and love waves we use cross correlations of ambient seismic noise between pairs of 158 broadband and short period sensors to investigate velocity structure over the top 5 10 km of the crust in the southern california plate boundary region around the san jacinto fault zone sjfz from the 9 component correlation tensors associated with all station pairs we derive dispersion curves of rayleigh and love wave group velocities the dispersion results are inverted first for rayleigh and love waves group velocity maps on a 1 5 1 5 km2 grid that includes portions of the sjfz the san andreas fault saf and the elsinore fault we then invert these maps to 3d shear wave velocities in the top 7 km of the crust the distributions of the rayleigh and love group velocities exhibit 2 azimuthal anisotropy with fast directions parallel to the main faults and rotations in complex areas the reconstructed 3d shear velocity model reveals complex shallow structures correlated with the main geological units and strong velocity contrasts across various fault sections along with low velocity damage zones and basins the sjfz is marked by a clear velocity contrast with higher v s values on the ne block for the section se of the san jacinto basin and a reversed contrast across the section between the san jacinto basin and the saf velocity contrasts are also observed along the southern parts on the saf and the elsinore fault with a faster southwest block in both cases the region around the salton trough is associated with a significant low velocity zone strong velocity reductions following flower shape with depth are observed extensively around both the sjfz and the saf and are especially prominent in areas of geometrical complexity in particular the area between the sjfz and the saf is associated with an extensive low velocity zone correlated with diffuse seismicity at depth and a similar pattern including correlation with deep diffuse seismicity is observed on a smaller scale in the trifurcation area of the sjfz these results augment local earthquake tomography images that have low resolution in the top few km of the crust and provide important constraints for studies concerned with behavior of earthquake ruptures generation of rock damage and seismic shaking hazard in the region

local wave propagation near the san jacinto fault zone southern california observations from a three component seismic array we present results from a study conducted to characterize the p and s wave trains and codas for local earthquakes observed near the san jacinto fault zone southern california the data were recorded by a small aperture three component seismic array and analyzed using a statistical array processing algorithm that provides estimates of the propagation direction apparent wavenumber and polarization characteristics for plane wave arrivals observed at the array the p codas for these local earthquake data are similar in that each is composed of predominantly p waves traveling in a direction subparallel to the path of the direct p arrivals these p coda exhibit a character consistent with propagation in a waveguide as opposed to propagation in a medium with randomly distributed isotropic scattering sources the s codas differ from the p codas in two dramatic ways 1 the s codas are composed of predominantly s waves and 2 the s coda waves arrive from more random spatially uniform directions the dramatic differences between the p and s codas provide compelling evidence that p and s coda are the product of distinctly different scattering mechanisms and therefore that the p and s codas provide information about different source characteristics and or structural features a third important observation concerning the s coda is that the direction of arrival spectra for the s codas differ from event to event considerably more so than do those of the p codas this observation is at odds with the conventional wisdom and suggests that the character of the s coda reflects a potentially complex interaction among several factors including but not limited to the source depth the source distance and the source radiation pattern

seismic velocity changes caused by the earth tide ambient noise correlation analyses of small array data we examine seismic velocity changes due to the earth tide by conducting cross correlation function ccf analyses of ambient seismic noise recorded at a small array composed of seven seismometers in northeastern japan we calculate ccfs for the dilatational and contractional episodes that are predicted from theoretical tidal volumetric strains ccfs of the two episodes are highly correlated but tiny differences are found in their phases the phase differences are explained by seismic velocity changes of 0 19 0 06 at 1 2 hz which are interpreted to be caused by opening closure of cracks or pores in the shallow subsurface due to the tidal strain strain sensitivities of the seismic velocity changes are estimated to be 6 9 104 strain 1 which are almost consistent with those reported in previous studies using artificial sources

seismic velocity structures in the southern california plate boundary environment from double difference tomography summary we present tomographic images of crustal structures in the southern california plate boundary area with a focus on the san jacinto fault zone sjfz based on double difference inversions of earthquake arrival times absolute arrival times of 247 472 p and 105 448 s wave phase picks for 5493 earthquakes recorded at 139 stations in southern california are used starting with a layered 1 d model and continuing in later iterations with various updated initial models we invert the data for vp and vs in a 270 km long 105 km wide and 35 km deep volume around the sjfz using a spatially variable grid with higher density around the sjfz the examined volume stretches from cajon pass to the northernmost imperial fault zone and includes portions of the southern san andreas fault saf the elsinore fault and the brawley seismic zone in the salton trough because differential traveltimes used in the double difference inversions are most sensitive to near source structures we obtain high resolution around the earthquake sources after 30 iterations we improve the average traveltime misfit by a factor of 16 though ray coverage is limited at shallow depths we obtain detailed images of seismic velocities from 3 to 20 km throughout much of the study area our final velocity results show zones of low velocity and anomalous vp vs ratios associated with various fault strands and sedimentary basins along with clear velocity contrasts across the sjfz and the southern saf the velocity reductions in fault zone regions are generally highest in geometrically complex areas up to 30 50 per cent in the top few kilometres are higher for vs than for vp and follow a flower type pattern with depth in the central section of the sjfz from the san jacinto valley to the trifurcation area the northeast side of the fault has generally higher seismic velocities than the southwest block the obtained contrasts of vp are more persistent and higher up to 20 per cent than the contrasts of vs up to 15 per cent although the differences may stem at least partially from the higher resolution of vp images in the sjfz sections to the northwest and southeast there are patches with reversed velocities contrasts especially in the shallow crust near the san jacinto valley and other basins along the banning fault there is no clear velocity contrast for the southern saf the northeast side has generally lower seismic velocities in the seismogenic zone with patches of contrast reversals in the shallow crust in the brawley seismic zone the northeast side has somewhat lower velocities in the 20 km section near the southern saf and higher velocities farther to the southwest the imaged features have important implications for various aspects of earthquake and crustal dynamics in the region

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

mapping pressurized volcanic fluids from induced crustal seismic velocity drops volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth here we show that the extent of the regions affected by pressurized fluids can be imaged through the measurement of their response to transient stress perturbations we used records of seismic noise from the japanese hi net seismic network to measure the crustal seismic velocity changes below volcanic regions caused by the 2011 moment magnitude m w 9 0 tohoku oki earthquake we interpret coseismic crustal seismic velocity reductions as related to the mechanical weakening of the pressurized crust by the dynamic stress associated with the seismic waves we suggest therefore that mapping seismic velocity susceptibility to dynamic stress perturbations can be used for the imaging and characterization of volcanic systems

assessment of resolution and accuracy of the moving window cross spectral technique for monitoring crustal temporal variations using ambient seismic noise summary temporal variations in the elastic behaviour of the earth s crust can be monitored through the analysis of the earth s seismic response and its evolution with time this kind of analysis is particularly interesting when combined with the reconstruction of seismic green s functions from the cross correlation of ambient seismic noise which circumvents the limitations imposed by a dependence on the occurrence of seismic events in fact because seismic noise is recorded continuously and does not depend on earthquake sources these cross correlation functions can be considered analogously to records from continuously repeating doublet sources placed at each station and can be used to extract observations of variations in seismic velocities these variations however are typically very small of the order of 0 1 per cent such accuracy can be only achieved through the analysis of the full reconstructed waveforms including later scattered arrivals we focus on the method known as moving window cross spectral analysis that has the advantage of operating in the frequency domain where the bandwidth of coherent signal in the correlation function can be clearly defined we investigate the sensitivity of this method by applying it to microseismic noise cross correlations which have been perturbed by small synthetic velocity variations and which have been randomly contaminated we propose threshold signal to noise ratios above which these perturbations can be reliably observed such values are a proxy for cross correlation convergence and so can be used as a guideline when determining the length of microseismic noise records that are required before they can be used for monitoring with the moving window cross spectral technique

surface wave tomography from microseisms in southern california received 5 april 2005 revised 23 may 2005 accepted 9 june 2005 published 26 july 2005 1 since it has already been demonstrated that point topoint seismic propagation green functions can be extracted from seismic noise it should be possible to image earth structure using the ambient noise field seismic noise data from 148 broadband seismic stations in southern california were used to extract the surface wave arrival times between all station pairs in the network the seismic data were then used in a simple but densely sampled tomographic procedure to estimate the surface wave velocity structure within the frequency range of 0 1 0 2 hz for a region in southern california the result compares favorably with previous estimates obtained using more conventional and elaborate inversion procedures this demonstrates that coherent noise field between station pairs can be used for seismic imaging purposes citation sabra k g p gerstoft p roux w a kuperman and m c fehler 2005 surface wave tomography from microseisms in southern california geophys res lett 32 l14311 doi 10 1029 2005gl023155

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

depth sensitivity of seismic coda waves to velocity perturbations in an elastic heterogeneous medium summary numerous monitoring applications make use of seismic coda waves to evaluate velocity changes in the earth this raises the question of the spatial sensitivity of coda wave based measurements here we investigate the depth sensitivity of coda waves to local velocity perturbations using 2 d numerical wavefield simulations we calculate the impulse response at the surface before and after a slight perturbation of the velocity within a thin layer at depth is introduced we perform a parametric analysis of the observed apparent relative velocity changes e obs versus the depth of the thin perturbed layer through the analysis of the decay of e obs we can discriminate two different regimes one for a shallow perturbation and the other for a deep perturbation we interpret the first regime as the footprint of the 1 d depth sensitivity of the fundamental surface wave mode to interpret the second regime we need to model the sensitivity of the multiply scattered body waves in the bulk we show that the depth sensitivity of coda waves can be modelled as a combination of bulk wave sensitivity and surface wave sensitivity the transition between these two regimes is governed by mode conversions due to scattering we indicate the importance of surface waves for the sensitivity of coda waves at shallow depths and at early times in the coda at later times bulk waves clearly dominate the depth sensitivity and offer the possibility of monitoring changes at depths below the sensitivity of the surface waves based on the transition between the two regimes we can discriminate a change that occurs at the surface from a change that occurs at depth this is illustrated for shallow depth perturbations through an example from lunar data

lunar subsurface investigated from correlation of seismic noise by correlating seismic noise recorded by four sensors placed on the moon during the apollo 17 mission we have retrieved a well defined dispersed rayleigh wave pulse inversion of its group velocity provides new constraints on the lunar subsurface structure the estimated signal to noise ratio snr of the retrieved rayleigh wavetrain is strongly dependent on solar illumination effectively making solar heating a source of seismic noise on the moon this result suggests that in future planetary missions it is feasible to extract information on the internal structure of extraterrestrial objects by correlating seismic noise even when natural quakes are absent

coseismic and postseismic elastic wave velocity variations caused by the 2008 iwate miyagi nairiku earthquake japan 1 we analyze coseismic and postseismic velocity variations caused by the june 13 2008 iwate miyagi nairiku earthquake mw 6 9 using passive image interferometry pii seismic noise is correlated in order to reconstruct the green s function between two sensors shear wave velocity changes are determined by relating the coda parts of the daily green s functions to a long term reference green s function our study extends from january 2008 to august 2010 and includes the correlations for 190 station pairs in three different frequency ranges from 0 125 to 1 0 hz we show that combining the 9 different component cross correlation functions stabilizes the velocity change estimation and increases analysis resolution the observed velocity change curves can be fitted by model time series consisting of a coseismic velocity drop followed by logarithmic postseismic recovery and seasonal velocity variations the coseismic velocity drops are stronger at higher frequencies and are concentrated in the southern part of the fault zone a tomography algorithm was developed to reproject the observed velocity variations of the different sensor pairs onto the single sensors the depth distribution of coseismic changes was modeled for the three stations with the largest velocity drops at two stations the coseismic velocity changes are located in the upper several hundred meters the third station shows indications for deeper changes in the order of kilometers postseismic recovery takes significantly longer than the analyzed two year period seasonal velocity variations with periods of one year are observed at all analyzed frequencies for most station pairs

variations of crustal elastic properties during the 2009 l aquila earthquake inferred from cross correlations of ambient seismic noise 1 we retrieve seismic velocity variations within the earth s crust in the region of l aquila central italy by analyzing cross correlations of more than two years of continuous seismic records the studied period includes the april 6 2009 mw 6 1 l aquila earthquake we observe a decrease of seismic velocities as a result of the earthquake s main shock after performing the analysis in different frequency bands between 0 1 and 1 hz we conclude that the velocity variations are strongest at relatively high frequencies 0 5 1h z suggesting that they are mostly related to the damage in the shallow soft layers resulting from the co seismic shaking citation zaccarelli l n m shapiro l faenza g soldati and a michelini 2011 variations of crustal elastic properties during the 2009 l aquila earthquakeinferred from cross correlations of ambient seismic noise geophys res lett 38 l24304 doi 10 1029 2011gl049750

comprehensive observation and modeling of earthquake and temperature related seismic velocity changes in northern chile with passive image interferometry we report on earthquake and temperature related velocity changes in high frequency autocorrelations of ambient noise data from seismic stations of the integrated plate boundary observatory chile project in northern chile daily autocorrelation functions are analyzed over a period of 5 years with passive image interferometry a short term velocity drop recovering after several days to weeks is observed for the mw 7 7 tocopilla earthquake at most stations at the two stations pb05 and patcx we observe a long term velocity decrease recovering over the course of around 2 years while station pb05 is located in the rupture area of the tocopilla earthquake this is not the case for station patcx station patcx is situated in an area influenced by salt sediment in the vicinity of salar grande and presents a superior sensitivity to ground acceleration and periodic surface induced changes due to this high sensitivity we observe a velocity response of several regional earthquakes at patcx and we can show for the first time a linear relationship between the amplitude of velocity drops and peak ground acceleration for data from a single station this relationship does not hold true when comparing different stations due to the different sensitivity of the station environments furthermore we observe periodic annual velocity changes at patcx analyzing data at a temporal resolution below 1 day we are able to identify changes with a period of 24 h too the characteristics of the seismic velocity with annual and daily periods indicate an atmospheric origin of the velocity changes that we confirm with a model based on thermally induced stress this comprehensive model explains the lag time dependence of the temperature related seismic velocity changes involving the distribution of temperature fluctuations the relationship between temperature stress and velocity change plus autocorrelation sensitivity kernels

the role of diffusion during carbonate diagenesis abstract the dissolution reprecipitation process which characterizes the early mineralogical stabilization of carbonate sediments takes place in a somewhat open chemical system studies of the trace element chemistries and isotopic compositions of carbonate grains before and after stabilization have documented the exchange of ions between the diagenetic site and the aquifer solution if the pores at reaction zone and in the immediate neighborhood of the diagenetic site are of insufficient diameter to allow effective solution flow the exchange of ions between the diagenetic site and the aquifer solution the large volume of water which flows through the macropores of the carbonate sediment takes place by aqueous diffusion this paper examines diffusion applied specifically to the conditions of carbonate diagenesis the diffusion equation modified to these circumstances serves as a guide to understanding the diffusion process at a given temperature three variables determine the efficacy of diffusion the diffusion coefficient the pore path and geometry and the concentration gradient the diffusion coefficient may be considered a measure of the inherent velocity at which a given ion travels under standard conditions the double positive cations common in carbonates ca2 sr2 ba2 zn2 mg2 etc and the carbonate anion all have similar diffusion coefficients thus this term of the equation exerts little influence during normal carbo ate diagenesis the pore path and geometry refer to the distance from aquifer to reaction zone and the diameter shape and directness of the pore passage this term is difficult to quantify in diagenetic systems but is constant for different ions at a single diagenetic site the longer and the more complex the path the less effective diffusion is there is a general facies dependence to this term grainstones have short paths from reaction zone to aquifer due to their permeability whereas mudstones and wackestones are characterized by long and torturous paths through the mud grains to the aquifer solution exchange of ions in the fast situation is more effective than in the second the concentration gradient the difference between the concentration of an ion in th reaction zone and in the proximal aquifer solution is the most variable parameter in diffusion the sign of the gradient which may be positive or negative indicates the direction of diffusion transport of the ions toward the region of lower concentration one cation may diffuse from the reaction zone while simultaneously a second cation diffuses toward the reaction zone this two way traffic has been documented in diagenetic calcite corals sr2 diffuses away from and mg2 diffuses toward the diagenetic site additionally one cation may diffuse effectively whereas a second diffuses ineffectively the latter species being characterized by a weaker concentration gradient thus a given diagenetic site may be chemically open for one cation and simultaneously somewhat closed for another application of diffusion principles to the aragonite calcite transformation during early diagenesis indicates the compositions of solutions and diagenetic calcites undergo temporal changes early on with few active diagenetic sites sr2 diffuses effectively from the reaction zone to the aquifer since there is a steep concentration gradient diagenetic calcites are relatively low in sr2 because of its effective removal from the diagenetic site as the number of active diagenetic sites increases so much sr2 may be delivered to the aquifer that sr2 builds up in the aquifer solution and the concentration gradient shallows diffusion from individual sites becomes less effective sr2 concentrates in the reaction zone and diagene ic calcites enriched in sr2 are produced as more and more aragonite is consumed a final phase is reached in which less total sr2 is delivered to the aquifer and the system returns to the conditions characteristic of the early phase