improvements to regional explosion identification using attenuation models of the lithosphere 1 regional p s amplitudes have been recognized as an effective discriminant between earthquakes and explosions while closely spaced events generally discriminate easily the application of this technique to broad regions has been hampered by large variations in the amplitude of phases due to the attenuation of the crust and upper mantle making use of a recent p wave and s wave attenuation model of the lithosphere we have found that correcting the events using our amplitude methodology significantly reduces the scattering in the earthquake population we demonstrate an application of this technique to station nil using broad area earthquakes and the 1998 indian nuclear explosion using the pn lg discriminant in the 1 2 hz passband we find that the explosion which is lost in the scatter of the earthquakes in the uncorrected discriminant clearly separates by correcting for attenuation structure we see a similar reduction in scatter and separation for the pn sn and pg lg discriminants

phenomenology and modeling of explosion generated shear energy for the source physics experiments abstract we present a mechanism for shear wave generation from buried explosions as part of the source physics experiment spe series the spe series includes sensitized heavy ammonium nitrate fuel oil sources of various sizes detonated in a borehole in the jointed climax stock granite the cylinder shaped shots were grouted in the borehole to couple the energy to the rock a high fidelity site model with explicit inclusion of the cylindrical explosive the grout filled borehole and site joint sets was included in a numerical simulation that mimics the near field velocity environment measured by an array of in ground accelerometers this approach was accommodated through a coupled euler lagrange code that allows simultaneous solving of a euler domain to model the high deformation source region and a lagrange domain that includes the complex geology with full contact specific laboratory measured geomechanical properties for the rock and the joint sets were included in the model the simulations compare favorably to the data and provide a possible physical mechanism for unexpected shear motion through the release of stored shear strain on the joints this research will advance our understanding of explosion generated shear wave energy from low yield nuclear tests

mass mortality following disturbance in holocene coral reefs from papua new guinea the frequency and intensity of disturbance on living coral reefs have been accelerating for the past few decades resulting in a changed seascape what is unclear but vital for management is whether this acceleration is natural or coincident only with recent human impact we surveyed nine uplifted early to mid holocene 11 000 3700 calendar cal yr b p fringing and barrier reefs along similar to 27 km at the huon peninsula papua new guinea we found evidence for several episodes of coral mass mortality but frequency was 16 km along the ancient coastline occurred ca 9100 9400 cal yr b p and is associated with a volcanic ash horizon recolonization of the reef surface and resumption of vertical reef accretion was rapid 100 yr but the post disturbance reef communities contrasted with their pre disturbance counterparts assessing the frequency nature and long term ecological consequences of mass mortality events in fossil coral reefs may provide important insights to guide management of modern reefs in this time of environmental degradation and change

factors controlling sediment preservation on a north jamaican fringing reef a process based approach to microfacies analysis abstract compositional characteristics of limestones are fundamental to the interpretation of depositional environments with an assumption that preserved grain assemblages preserve sufficient evidence of initial sediment input to enable delineation of environments it is acknowledged however that a range of early diagenetic processes including encrustation fragmentation abrasion microboring dissolution cementation and recrystallization may influence grain preservation potential and thus bias the composition of resultant grain assemblages this study examines the effects and relative importance of a range of early diagenetic processes across a fringing reef at discovery bay north jamaica physical processes abrasion and fragmentation are most important at shallow fore reef sites whilst back reef sites are dominated by biochemical processes including microboring recrystallization biofilm related calcification and dissolution grain susceptibility to each process is highly variable and influenced by mineralogy and skeletal structure coral fragments for example are most susceptible to the effects of microboring whereas halimeda plates are most susceptible to dissolution extensive alteration of grain assemblages is predicted within the back reef where dissolution of coral and halimeda occurs because of intense microboring and pore water undersaturation fore reef assemblages by contrast remain relatively unaltered results have implications both for improved ecological interpretation of carbonate sedimentary sequences and for understanding of how and why carbonate microfacies develop

global change and modern coral reefs new opportunities to understand shallow water carbonate depositional processes human activities are impacting coral reefs physically biologically and chemically nutrification sedimentation chemical pollution and overfishing are significant local threats that are occurring worldwide ozone depletion and global warming are triggering mass coral bleaching events corals under temperature stress lose the ability to synthesize protective sunscreens and become more sensitive to sunlight photo oxidative stress also reduces fitness rendering reef building organisms more susceptible to emerging diseases increasing concentration of atmospheric co2 has already reduced caco3 saturation in surface waters by more than 10 doubling of atmospheric co2 concentration over pre industrial concentration in the 21st century may reduce carbonate production in tropical shallow marine environments by as much as 80 as shallow water reefs decline worldwide opportunities abound for researchers to expand understanding of carbonate depositional systems coordinated studies of carbonate geochemistry with photozoan physiology and calcification particularly in cool subtropical transition zones between photozoan reef and heterotrophic carbonate ramp communities will contribute to understanding of carbonate sedimentation under environmental change both in the future and in the geologic record cyanobacteria are becoming increasingly prominent on declining reefs as these microbes can tolerate strong solar radiation higher temperatures and abundant nutrients the responses of reef dwelling cyanobacteria to environmental parameters associated with global change are prime topics for further research with both ecological and geological implications

simulation of topographic effects on seismic waves from shallow explosions near the north korean nuclear test site with emphasis on shear wave generation 1 we performed high resolution 8 hz three dimensional simulations of ground motions from shallow explosions in the presence of rough surface topography near the north korean nuclear test site to study elastic propagation effects with emphasis on theoretical aspects of shear wave generation interaction with rough topography causes significant p to rg scattering along the surface with amplification of high frequency 2 8 hz shear waves relative to the flat earth case shear waves of different polarizations are coupled by topographic scattering rg precursors composed of p to rg conversions traveling as surface waves have the spectral amplitudes comparable to the p wave while the rg phase has the low frequency 0 5 3 hz spectral shape of the rg from the flat case plus the high frequency 3 8 hz p wave spectra motions at near vertical takeoff angles corresponding to teleseismic propagation are increased or decreased indicating that waves are focused or defocused by topographic features above the source topographic roughness has a dramatic effect as short wavelength features 2 5 km are included higher frequencies are amplified by topography including frequencies corresponding to wavelengths shorter than the shortest topographic scale length overall topography enhances energy propagating along the surface near the source amplifies surface waves and tends to balance sv and sh polarized motions all of which impact shear wave observations used for nuclear explosion monitoring further simulation studies could elucidate how the wavefield emerging from a topographically rough area ultimately propagates to regional and or teleseismic distances

fine grained carbonates in nearly closed reef environments mataiva and takapoto atolls central pacific ocean abstract the nature origin and mode of accumulation of fine grained carbonate sediments have been investigated in the nearly enclosed lagoons of two french polynesian atolls mataiva and takapoto the fine sized fraction 20 m is substantially higher in amount 70 of the total fine sediments on average than the mud portion and may increase volumetrically 90 99 in some localities aragonite is the predominant mineral present 90 of the total calcium carbonate the fines appear to be mainly skeletally derived the silt fraction includes coral and molluscan detritus sponge chips juvenile benthic foraminiferans and other biogenic debris the mud is chiefly composed of aggregated nanograins ascidian spicules skeletal nanograins coral generated mainly and coccoliths a minor part of the mud is certainly of non skeletal origin some portion of freely deposited fines fill cavities or are attached upon sand grain surfaces they are associated with scattered inorganic precipitates and contribute to the formation of micrite envelopes and aggradation of host grains such a process is highly significant in the total carbonate budget of the reef the fine carbonate sediments result directly from the biological disintegration of nearby buildups mainly through the boring activity of sponges and lithophagid molluscs we suggest that the authigenic mud sized crystallites are controlled in their precipitation both by carbonate supersaturation and anoxic conditions seasonally affecting the interstitial sediment waters enclosed atoll lagoons are relatively self governing environments of deposition which are influenced by long term quiescent water situations rather than by rare catastrophic events

seismic decoupling with chemical and nuclear explosions in salt an extensive series of simulations was performed of underground explosions in salt using both chemical and nuclear explosives in both cases the radius of the initial emplacement cavity was varied from the fully tamped configuration to as large as 80 m kt sup 1 3 when not fully tamped the cavity was assumed initially to contain air at ambient temperature and pressure in the nuclear source case the simulations are shown to be in good agreement with the salmon sterling events conducted by the united states and with recently released russian data on a similar pair of explosions in an azgir salt dome simulation of the us cowboy series of chemical explosions in a louisiana salt mine are also shown to be in very good agreement with the experimental data however the constitutive model for the salt that best explains these data is different from that derived for salmon both salt models are amply supported by laboratory and field data the main result of these simulations is that cavity decoupling with chemical explosives is much less efficient than with nuclear explosives although maximum decoupling factors f sub max near 200 may be attainable with either of the two sources the cavity size required to achievemore this value appears to be 40 m kt sup 1 3 for cavity radii half as large f sub max is roughly 4 times lower with nuclear explosives and lower by another factor of 4 with chemical sources moreover if the initial cavity radius is a more modest 10 m kt sup 1 3 f sub max 3 even with a nuclear source 24 refs 8 figs less

multi scale fracture damage associated with underground chemical explosions abstract understanding rock damage induced by explosions is critical for a number of applications including the monitoring and verification of underground nuclear explosions mine safety issues and modeling fluid flow through fractured rock we use core observations televiewer logs and thin section observations to investigate fracture damage associated with two successive underground chemical explosions spe2 and spe3 in granitic rock at both the mesoscale and microscale we compare the frequency and orientations of core scale fractures and the frequency of microfractures between a pre experiment core and three post experiment cores natural fault zones and explosion induced fractures in the vicinity of the explosive source are readily apparent in recovered core and in thin sections damage from faults and explosions is not always apparent in fracture frequency plots from televiewer logs although orientation data from these logs suggests explosion induced fracturing may not align with the pre existing fracture sets core scale observations indicate the extent of explosion induced damage is 10 0 m after spe2 and 6 8 m after spe3 despite both a similar size and location for both explosions at the microscale damage is observed to a range distance of 10 2 0 9 m after spe2 and 16 6 0 9 and 11 2 0 6 in two different cores collected after spe3 additional explosion induced damage interpreted to be the result of spalling is readily apparent near the surface but only in the microfracture data this depth extent and intensity of damage in the near surface region also increased after an additional explosion this study highlights the importance of evaluating structural damage at multiple scales for a more complete characterization of the damage and particularly shows the importance of microscale observations for identifying spallation induced damage

platforms of the nicaraguan rise examples of the sensitivity of carbonate sedimentation to excess trophic resources the nicaraguan rise is an active tectonic structure in the western caribbean carbonate accumulation on its platforms has not kept pace with relative holocene sea level rise despite a tropical location remote from terrigenous sedimentation trophic resources apparently exceed levels favoring coral reef development because sponge algal communities dominate the drowning western platforms in contrast to mixed coral algal benthos on pedro bank and well developed coral reefs along the north coast of jamaica concentrations of biotic pigments in sea surface waters show a corresponding west east gradient oceanic waters flowing over the western banks carry nearly twice as much biotic pigment as oceanic waters north of jamaica sources enriching the western caribbean are terrestrial runoff upwelling off northern south america and topographic upwelling over the nicaraguan rise that relatively modest levels of trophic resources can suppress coral reef development holds important implications for understanding carbonate platform drownings in the geologic record

effects of rock damage on seismic waves generated by explosions in studying the physical processes involved in the generation of seismic waves by explosions it is important to understand what happens in the region of high stresses immediately surrounding the explosion this paper examines one of the processes that takes place in this region the growth of pre existing cracks which is described quantitatively as an increase in rock damage an equivalent elastic method is used to approximate the stress field surrounding the explosion and a micro mechanical model of damage is used to calculate the increase in damage simulations for a 1 kt explosion reveal that the region of increased damage can be quite large up to ten times the cavity radius the damage is initiated on a damage front that propagates outward behind the explosive stress wave with a velocity intermediate between that of p and s waves calculations suggest that the amount of increased damage is controlled primarily by the initial damage and the extent of the region of increased damage is controlled primarily by the initial crack radius the motions that occur on individual cracks when damage increases are converted to seismic moment tensors which are then used to calculate secondary elastic waves which radiate into the far field it is found that while the contribution from an individual crack is small the combined effect of many cracks in a large region of increased damage can generate secondary waves that are comparable in amplitude to the primary waves generated by the explosion provided that there is asymmetry in the damage pattern this process is quite effective in generating s waves thus providing a quantitative explanation of how s waves can be generated by an explosion two types of asymmetry are investigated a shear pre stress and a preferred orientation of cracks and it is found that both produce similar effects

controls on grain size patterns in periplatform carbonates marginal setting versus glacio eustacy the importance of grain size as a fundamental property controlling other physically derived properties is well known recent grain size studies on periplatform sediments of the caribbean and western north atlantic have shown that grain size variability is coupled with changes in carbonate platform productivity and export in response to pleistocene holocene glacio eustacy these findings showed that periplatform sediments are dominated by fine grained material during sea level highstands and coarser material during sea level lowstands this paper addresses the question of grain size patterns in periplatform settings and their relationship to glacio eustacy furthermore it considers whether these patterns are applicable to different types of margin settings accretionary erosional here existing data pleistocene holocene from the accretionary western leeward margin of great bahama bank odp leg 166 and new data from the erosional eastern windward margin odp leg 101 are used the results show that the grain size patterns of both margins are controlled by late neogene sea level fluctuations the accretionary leeward margin sediments indicate the same grain size pattern as previously described in the literature however the erosional windward margin shows a reverse pattern with coarser sediments in interglacials and finer deposits in glacials this proposes that the leeward margin grain size pattern is controlled by the productivity export mode of the platform this is indicated by the platform top derived fine muds transported off bank to form a thick sediment wedge on the low angled slope during interglacials in contrast on the windward margin the sediment flux pattern is controlled by the impact of mass transport processes this is indicated by the increased occurrence of turbidites during interglacials that might be more frequent at this time because the steep angled erosional slope is less apt for the deposition of excess fine material this material is eroded and or bypasses the slopes and is redeposited in the periplatform basin setting

can the fisk conjecture be explained by rock damage around explosions we investigate the possibility that rock damage ashby and sammis 1990 johnson and sammis 2001 can explain recent observations of fisk 2006 2007 that p and s wave corner frequencies from explosions differ by a factor approximately related to the ratio of near source compressional and shear velocities the fisk conjecture the observation of differing p and s wave corner frequencies from explosions forms the basis for the success of the high frequency p s discriminant using first order considerations we find that the damage mechanics model can indeed explain the fisk conjecture although this is certainly not a unique explanation the key to our argument is that although the radius of rock damage is less than that of the so called elastic radius the slow velocity of the outward propagating damage front can reduce shear wave corner frequencies this explanation differs slightly from that of fisk 2006 2007 who states that s waves from explosions occur at a similar length scale comparable to the elastic radius as for p waves because of the significant reduction in v s caused by rock damage we suggest that the shear waves generated within the damage region can have a radius significantly less than the elastic radius for a p wave additionally because rock damage is controlled by the difference of the maximum and minimum principal stress first order considerations suggest that lithospheric overburden does not shut off rock damage until scaled depths of burial of up to graphic 1 thus effects due to rock damage may be an important source of shear waves for nearly all tamped nuclear explosions for which we have experience 1 embed inline graphic 1 gif

production and cycling of calcium carbonate in a shelf edge reef system st croix u s virgin islands applications to the nature of reef systems in the fossil record abstract geologic reefs are the end products of not only constructive processes that produce calcium carbonate but also of destructive processes e g bioerosion and wave action that reduce solid substrate to sediment and of physical processes that rework the reef fabric and transport sediment a study was conducted at cane bay on the island of st croix u s virgin islands to quantify the suite of processes that have influenced holocene reef development data on carbonate production reef accretion bioerosion and sediment transport were used to construct a detailed carbonate budget and to apply the findings of this study to the character of reefs observed in the fossil record total carbonate production on the reef ranged from 0 to 5 78 kg m2 per year with a reef wide average of 1 21 kg m2 per year 1 13 by corals 0 02 by coralline algae 0 06 by primarily molluscs forams and echinoderms based on 7 cores only 0 91 kg m2 per year of this have been retained within the reef interior the remaining 0 24 kg m2 per year of sediment along with the 0 06 kg m2 per year contributed directly by molluscs etc are deposited within reef channels and are probably flushed from the reef by major storms of the material recovered in the cores 58 was either loose sediment and rubble or open void space much of the recognizable coral material was demonstrably reworked and out of place accretion rates across the shelf generally increased with water depth as a result of active slumping along the steepening reef face over the past 2 000 3 000 years the importance of detrital material in the reef fabric and the major role played by secondary processes that constantly rework the substrate have resulted in a reef whose interior is more of a garbage pile than an in place assemblage of corals cemented together into a rigid framework the physical similarities between the detrital fabric of the reef at cane bay and those found in many ancient deposits imply that the general processes operating along the cane bay shelf have persisted during much of the evolution of ancient reefs it is proposed that our modern models overemphasize the importance of in place framework as a criterion for an ecologic reef

sediments from fringing reefs of reunion island indian ocean abstract on reunion island fringing reefs comprise the following physiographical zones from the open sea landwards outer sandy spread spur and groove zone reef flat backreef zone sixty two samples collected from the various zones have been analyzed by using correspondence factor analysis to determine variations in sediment composition and grain size five sediment facies and three foraminiferal subfacies can be recognized on the basis of component composition and three sediment types can be defined using the grain size data alcyonaria terrigenous fine sand facies and calcarina subfacies occur in the outer sandy spread whereas foraminiferal coarse sand facies characterizes the spur and groove system the outer margin of the reef flat exhibits coral coralline algal and coral molluscan coarse sand facies and the inner part of the reef flat exhibits a coral terrigenous mediumsand facies the whole reef flat also presents a miniacina subfacies the backreef area displays a coral coralline algal medium sand facies and a marginopora textularia subfacies factor axes seem to reflect physiographical or hydrodynamical gradients

heterozoan carbonates from the equatorial rocky reefs of the galapagos archipelago strongly influenced by seasonal and interannual i e el nino southern oscillation upwelling the equatorial setting of the galapagos archipelago is divided into well defined temperature nutrient and calcium carbonate saturation aragonite regions to understand the relationship between oceanographic properties and sediment grain associations grain size carbonate content and components from sea floor surface samples were analysed representing the main geographical regions of the galapagos archipelago the shallow water rocky reefs of the galapagos archipelago are characterized by mixed carbonate siliciclastic slightly gravelly sands despite minor differences in carbonate content major differences exist in the distribution and composition of key carbonate producing biota halimeda is absent and benthic foraminifera occur in extremely low abundance the western side of the galapagos archipelago is strongly influenced by nutrient rich low aragonite subtropical water which generates a heterozoan carbonate biofacies in a tropical realm resembling cold water counterparts i e serpulid echinoderm gastropod barnacle and bryozoan rich facies the central east region is composed of a transitional heterozoan biofacies biofacies observed in the northern region have an increased occurrence of tropical corals albeit with a minor overall contribution to the carbonate components although the temperature gradient would allow for a broader distribution of photozoan biofacies the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories mimicking cool water deeper or higher latitude environments the recent sedimentary record of the galapagos archipelago presents a range of tropical heterozoan carbonate communities responding to more than simply latitude or temperature but a much more complex mixture of physical evolutionary and geological processes

seismic imaging of santorini subsurface constraints on caldera collapse and present day magma recharge abstract volcanic calderas are surface depressions formed by roof collapse following evacuation of magma from an underlying reservoir the mechanisms of caldera formation are debated and predict differences in the evolution of the caldera floor and distinct styles of magma recharge here we use a dense active source seismic tomography study to reveal the sub surface physical properties of the santorini caldera in order to understand caldera formation we find a 3 km wide cylindrical low velocity anomaly in the upper 3 km beneath the north central portion of the caldera that lies directly above the pressure source of the 2011 2012 inflation we interpret this anomaly as a low density volume caused by excess porosities of between 4 and 28 with pore spaces filled with hot seawater vents that were formed during the first three phases of the 3 6 ka late bronze age lba eruption are located close to the edge of the imaged structure the correlation between older volcanic vents and the low velocity anomaly suggests that this feature may be long lived we infer that collapse of a limited area of the caldera floor resulted in a high porosity low density cylindrical volume which formed by either chaotic collapse along reverse faults wholesale subsidence and infilling with tuffs and ignimbrites phreatomagmatic fracturing or a combination of these processes phase 4 eruptive vents are located along the margins of the topographic caldera and the velocity structure indicates that coherent down drop of the wider topographic caldera followed the more limited collapse in the northern caldera this progressive collapse sequence is consistent with models for multi stage formation of nested calderas along conjugate reverse and normal faults the upper crustal density differences inferred from the seismic velocity model predict differences in subsurface gravitational loading that correlate with the location of 2011 2012 edifice inflation this result supports the hypothesis that sub surface density anomalies may influence present day magma recharge events we postulate that past collapses and the resulting topographical and density variations at santorini influence magma focusing between eruptive cycles a feedback process that may be important in other volcanoes

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

asperity model of an earthquake dynamic problem a previous study that presented the static solution for an asperity model of an earthquake is extended to solve the dynamic problem that develops when failure occurs on the boundary of an asperity patch and then spreads over the surrounding displacement shadow region the boundary integral equation method is coupled with basic constitutive equations for failure and friction to solve the dynamic problem with different parameters used for the strong asperity patch and weak shadow region no friction displacement weakening friction and velocity strengthening friction are all investigated depending on the type and amount of friction that is present the dynamic solutions for slip on the fault exhibit a range of different features including overshoot of the static solution and oscillation rupture front velocities that may be greater than or less than the s velocity and change with position and either total or partial release of the static moment common characteristics of the solutions are that failure on the asperity patch is almost independent of failure on the shadow region and that the displacement deficit on the shadow region is released by propagating slip pulses the stress concentrations of the asperity model are sufficient to produce nonlinear elastic effects in a region extending outward from the fault to distances comparable with the dimensions of the shadow region beginning with the solutions for slip on the fault waveforms are simulated for an earthquake of magnitude m w 1 44 and compared with data recorded at a distance of 8 65 km simulations that contain both source and propagation effects are capable of explaining most of the basic features of the observational data including general agreement with the shape of the waveforms in the time domain the levels and slopes of the spectra at low frequencies less than 10 hz and at high frequencies greater than 100 hz and some of the interference effects present in both the time and frequency domains

liquefaction limit during earthquakes and underground explosions implications on ground motion attenuation liquefaction of saturated soils and sediments documented during earthquakes shows an empirical relation log r max 2 05 0 10 0 45 m where r max is the liquefaction limit in meters i e the maximum distance from liquefaction site to the hypocenter and m is the earthquake magnitude combining this with an empirical relation between m and the seismic energy of an earthquake we obtain a relation between the liquefaction limit and the seismic energy e a r max the prefactor corresponds to a threshold energy for liquefaction ranging from 0 004 to 0 1 j m3 the exponent ranging from 3 2 to 3 3 implies that the energy density of ground motion attenuates with distance according to 1 r 3 2 3 3 where r is the distance from the hypocenter the value of the threshold energy suggests a preliquefaction degradation of the shear modulus of soils by more than 3 orders of magnitude liquefaction documented during underground explosions is characterized by a threshold energy several orders of magnitude greater than that for liquefaction during earthquakes but shows a similar functional relation between e and r max as that for liquefaction during earthquakes and implies a similar attenuation relation between ground motion energy density and distance

trace element mobility during spheroidal weathering of basalts and andesites in hawaii and guatemala abstract trace element mobility has been studied in spheroidally weathered corestone shell complexes developed on late tertiary and quaternary volcanic rocks the parent materials are basalts and andesites related to 1 a subduction zone tecuamburro and moyuta volcanoes guatemala and 2 a hot spot hawaiian islands of oahu maui and hawai i the initial major element compositions are largely preserved in the corestones each corestone sample shows major element abundances characteristic of the different magmatic processes through which the lavas were generated however the changes in trace element compositions due to weathering show similar patterns in the corestone shell complexes independent of the tectonic setting and age element mobility within the different corestone shell complex was determined using an isovolumetric reference frame in this method bulk density is chosen as an independent measure of the extent of weathering based on volumetric concentrations the notion of element immobility cannot be applied to all the corestone shell complexes elements commonly assumed to be immobile e g zr ti and al vary in volumetric concentration for some corestone shell complex despite petrographic evidence of only minor weathering two corestones oahu and tecuamburro have become enriched in ree 3 relative to other lava flows from the same volcanoes and display negative ce anomalies the exfoliated shells from these complexes tend to have lower concentrations of ree 3 and have positive ce anomalies the fractionation of ce from the other rare earth elements ree is inferred to be a manifestation of changes in the valence state of ce from trivalent to tetravalent under oxidizing conditions in settings where the development of corestone shell complex is advanced an acidic solution can mobilize trivalent ree leach them out of more extensively weathered materials and transport them to less acidic portions of the regolith undergoing incipient weathering the precipitation of the ree 3 in the rinds and centers of the corestones are likely due to increases of the ph of the weathering solution systematic weathering induced ree behavior enrichment of most ree with lesser ce enrichment resulting in a negative ce anomaly can be discerned even in corestone samples that exhibit major element abundances and petrographic features otherwise similar to unweathered basalts and andesites

inverting ground motion from a seismometer array to obtain the vertical component of rotation a test using data from explosions to study factors that affect reliability of the derived vertical rotational ground motions about vertical axis from translational array waveforms we have conducted a field test using explosion the dataset was collected on march 4 2008 from an active source experiment of the taiwan geodynamics research project taiger 2008 in which 750 kg of explosives were set off about 500 m away from a specially designed seismic array in free field consisting of 8 tri axial rotational sensors 13 tri axial accelerometers and 12 six channel 24 bit dataloggers with gps receivers our results show that the waveform fits were greatly improved when the explosion induced crustal strains were less than 2 10 5 for our station configuration as a result our modeling for the large amplitude part of the mainshock was not entirely successful however we have successfully recovered the first order features of the later part of the vertical rotational ground motions using translational velocity waveforms in the 0 5 20 hz bandwidth using the spudich and fletcher s procedure 2009 moreover we used a modified jaeger s 1969 formula and derived similar rotational synthetics we found that the best rotational rate waveform fits were derived using a station configuration of a dense small aperture translational array combined with a few largeoffset stations a small aperture array is needed to fulfill the uniform rotation assumption however inverting data from an array of small spatial dimension requires waveforms of high signal to noise ratio and high sampling rates surprisingly large offset translation stations provided additional constraints in time and space helping to fit the low frequency waveforms using the inverted result we forward predicted the vertical translational waveforms not used in the inversion and got excellent fits this suggests that the inverted results are of good quality for predicting the complete translational ground motions even though only horizontal components were used in the inversion array derived or directly measured rotational ground motions can be used to predict translational ground motions in the near by region lessons learned from this study could be helpful for future studies using translational ground motions to derive dynamic ground strains tilts and torsions

slow chemical weathering in a semiarid climate changes in the mineralogy and geochemistry of subaerial lava flows in the deschutes river basin central oregon abstract the progression of mineral alteration and chemical changes of thirteen pairs of fresh and weathered surficial lava samples from the deschutes river basin of central oregon were studied to understand incipient weathering in a semiarid climate samples range from basalt to dacite in composition and quaternary to late miocene in age only the tertiary samples showed significant chemical weathering based on element mobility and mineral alteration the slight climatic variations between tertiary outcrop locations map 38 74 cm yr and mat of 7 2 7 6 c did not correlate with degree of weathering the susceptibility sequence of phases was determined to be glass olivine plagioclase orthopyroxene clinopyroxene fe ti oxides the older weathered samples have experienced significant leaching of mobile cations e g ca mg sr resulting in a lower calculated weathering index the tertiary weathered samples are enriched in ree particularly lree which is attributed to a lree phosphate found in association with allophane clay mineralization in plagioclase these samples also have a negative ce anomaly likely due to its tetravalent state in oxidizing conditions and subsequent lack of mobility in weathering solutions although there is a clear petrographic and chemical distinction between fresh and weathered lavas 2 ma the distinction between fresh and weathered samples is not evident in the quaternary lavas significant element mobility between sample pairs is closely correlated to the breakdown of plagioclase and orthopyroxene and the subsequent secondary mineralization of clays and or lree rich phosphates with the exception of plagioclase all the mineral phases in the deschutes lavas have persistence times or stability of at least one and possibly several orders of magnitude greater than the same phases in soil chronosequences or weathering rinds in more temperate and humid climates as a result elemental release rates and silicate fluxes are much lower under semiarid conditions and their role in the global carbon cycle should be examined more closely

the micromechanics of westerley granite at large compressive loads the micromechanical damage mechanics formulated by ashby and sammis pure appl geophys 133 3 489 521 1990 has been shown to give an adequate description of the triaxial failure surface for a wide variety of rocks at low confining pressure however it does not produce the large negative curvature in the failure surface observed in westerly granite at high confining pressure we show that this discrepancy between theory and data is not caused by the two most basic simplifying assumptions in the damage model 1 that all the initial flaws are the same size or 2 that they all have the same orientation relative to the largest compressive stress we also show that the stress strain curve calculated from the strain energy density significantly underestimates the nonlinear strain near failure in westerly granite both the observed curvature in the failure surface and the nonlinear strain at failure observed in westerly granite can be quantitatively fit using a simple bi mineral model in which the feldspar grains have a lower flow stress than do the quartz grains the conclusion is that nonlinearity in the failure surface and stress strain curves observed in triaxial experiments on westerly granite at low loading rates is probably due to low temperature dislocation flow and not simplifying assumptions in the damage mechanics the important implication is that discrepancies between experiment and theory should decrease with increased loading rates and therefore the micromechanical damage mechanics as formulated can be expected to give an adequate description of high strain rate phenomena like earthquake rupture underground explosions and meteorite impact

shear waves from isotropically dominated sources comparison of the 2013 rudna poland and 2007 crandall canyon utah mine collapses comparison of observed and synthetic radiation patterns suggests that love waves generated by the 2007 crandall canyon mine collapse m w 4 1 are the result of shear waves generated by a relatively large compensated linear vector dipole component at the source whereas the love waves associated with a 2013 rudna mine collapse m w 4 2 are minimal except where amplified by a deep sedimentary basin we examine the source of the 19 march 2013 rudna mine poland collapse with a full moment tensor inversion method using the complete waveforms of regional distance seismic data the computed source is primarily composed of a dominant and statistically significant implosive component the rudna source is more similar to previous mine collapses than to double couple tectonic earthquakes although source mechanisms are similar there are clear differences in love wave amplitudes online material tables of velocity models and figures of moment tensors and waveform fits

weathering on land and transport of chromium to the ocean in a subtropical region misiones nw argentina a chromium stable isotope perspective abstract we have investigated the pathway of chromium from its mobilization on land and along its riverine transport in a subtropical region of south america misiones province argentina in an attempt to link cr stable isotope compositions recently measured in seawater with signals prevailing in rivers and ultimately with cr isotope effects observed during oxidative surface weathering in subtropical red soils cr concentrations and stable cr isotopic compositions expressed as 53cr values in two typical and representative surface profiles of weathered basalt show significant depletion of cr in the soils of up to 50 together with pronounced negatively fractionated 53cr values which are indicative of oxidative mobilization of heavy cr vi into the run off the behavior of cr in the studied weathering profiles is not correlated with that of other redox sensitive elements such as ce and u this is essentially due to the affinity of ree and u but not cr with secondary phosphates which form during weathering processes smaller tributaries in nw argentina to the parana river second largest river in south america carry dissolved cr in the order of 0 7 1 4 ppb 13 27 nm with 53cr values of 0 2 to 0 4 balancing the negatively fractionated weathering products the isotope composition and concentration of dissolved cr in the ca 1200 km long parana river from misiones to its estuary and discharge area into the south atlantic ocean remains relatively constant with an average cr concentration around 2 4 ppb 46 nm and an average 53cr value of 0 32 the cr concentration in the estuary itself drops by ca 50 but with only minor change in its cr isotope composition results from the parana estuary are identical with recently analyzed surface seawater from the argentine basin with cr contents of 0 3 ppb 6 nm and 53cr values 0 4 bonnand et al 2013 and indicate that there is only a minimal cr isotopic variability during riverine transport even during long transport distances as shown in our example of the parana river simple cr input flux calculations reveal that the parana river accounts for 5 of the total yearly cr flux to the world s oceans today and that its isotopic signature seems to be at least locally imparted to the surface seawater of the argentine basin whether or not this cr isotope signature is generally exhibited by the world s oceans needs further investigations particularly the characterization of seawater around the globe

corner frequency scaling of regional seismic phases for underground nuclear explosions at the nevada test site model fits are used to estimate source spectral corner frequencies of regional seismic phases pn pg and lg from underground nuclear explosions unes at the nevada test site nts based on recordings by lawrence livermore national laboratory llnl nts network stations the spectra are corrected for instrument response distance and station effects and then network averaged explicit information regarding geophysical working point properties depth of burial and some announced yields for nts explosions springer et al 2002 is utilized for the spectral modeling scaling of pn pg and lg corner frequencies with source yield is examined for sets of explosions at yucca flat pahute mesa and rainier mesa with similar material properties medium type density velocities and gas porosity the unes are limited to those in media with gas porosity of 10 or less so that a source spectral model with a rolloff of f 2 is applicable model comparisons are also examined for regional p lg discriminants a key result is that lg corner frequencies for ntsunes exhibit similar scaling with source size as for p waves but shifted lower analogous to observations by fisk 2006 for the lop nor semipalatinsk and novaya zemlya test sites this appears to corroborate an important effect that is that major contributions to s wave generation by explosions occur near the source with a similar length scale comparable to the elastic radius as for p waves from explosions although the explicit physical mechanism is not yet understood the implications are important regarding where and perhaps how s waves are predominantly generated by explosions a related key result is that the increasing separation of p lg at higher frequencies between nts explosions and earthquakes has a consistent model based explanation as at other nuclear test sites in terms of the difference between explosion p and s corner frequencies

missing molluscs field testing taphonomic loss in the mesozoic through early large scale aragonite dissolution as a field test for cherns and wright9s previously published hypothesis based on paleozoic faunas that the paucity of certain molluscan groups in the fossil record may be largely a taphonomic not ecologic effect a typical mesozoic molluscan dominated fauna is compared with its early silicified lagerstatten equivalent from a similar depositional setting a lower jurassic offshore carbonate ramp facies in south wales comprises alternating thin limestones and organic rich shales the former are largely diagenetic and carry marine isotopic signatures their typical fauna is mainly well preserved calcitic and bimineralic calcite aragonite epifaunal and semiinfaunal bivalves evidence of aragonitic shells is normally restricted to molds common in inner ramp settings in high energy skeletal grainstones but mostly poorly preserved and restricted to deep burrowing bivalves in offshore deposits however locally early silicification in offshore facies has preserved much more diverse faunas with abundant formerly aragonitic molluscs including many more infaunal burrowers it appears that major aragonite dissolution normally distorted both apparent diversity 65 decrease in bivalve diversity and the trophic structure of the offshore facies providing aragonite that probably sourced the diagenetic carbonates we suggest that aragonitic shells were selectively dissolved in the upper sediment column in lower energy settings where high organic contents favored microbial decay and acidity such early dissolution was absent from the higher energy facies that originally had low organic contents taphonomic loss through early skeletal aragonite dissolution was an equally important process in mesozoic offshore shelf environments and although still leaving depleted molluscan dominated faunas resulted in a massive distortion of diversity

geochemical anatomy of a spheroidally weathered diabase major trace element concentrations and nd sr isotope ratios were measured in micro drilled samples of a 237 ga old hand specimen sized spheroidally weathered diabase from southern india a sample of the un weathered diabase dike was also analyzed x ray micro ct imaging of the weathered sample shows three dominant mineral phases which are plagioclase pyroxene and a fe bearing phase possibly hematite and or ilmenite this imaging documents the pervasive nature of two generations of ribbon like cross cutting fractures the older fracture is sealed while the more recent fracture is open without any in filling the values of the chemical index of alteration cia of the samples show a wide range but are less than 50 despite being a relatively less weathered rock we observe that concentrations of major minor and trace elements vary significantly with the percentage relative standard deviation rsd for the elements ranging from 10 2 41 8 the cia of the samples do not show any trend with the position of the sample in the hand specimen barring ca and li whose concentrations decrease from the core to the rim of the sample there is no significant spatial trend in the concentrations of the elements concentrations of na al and sr increase with increasing cia values while concentrations of mg fe and sc decrease with increasing cia the strong positive correlations of na and al as well as na and sr indicates preferential weathering of plagioclase in the diabase na ca increases while mg al mg na mg ca fe al and sc sr decrease with increasing cia values and the un weathered rock plots in the middle of these trends such variations are explained in terms of differential weathering of plagioclase in samples with lower cia than the un weathered rock w1 type and pyroxene in samples with higher cia than the un weathered rock w2 type which have varying resistance to weathering at the hand specimen scale the variability in the weathering indices like cia are controlled by differential weathering of minerals and might not accurately reflect the intensity of weathering chondrite normalized la sm and gd lu co vary with cia values indicating mobility of the rees during spheroidal weathering even at the hand specimen scale the eu anomaly also increases with increasing cia values which is explained by differential weathering of pyroxene and plagioclase we observe large percentage deviations of the nb normalized concentrations of elements from the un weathered rock in specific samples but no spatial trend is observed overall the variations in element concentrations can be explained by varying fluid mobility of the elements selective weathering of the minerals in the diabase and ambient environmental conditions considerable nd and sr isotopic variability is observed at the hand specimen scale and is explained in terms of weathering related fractionation of parent daughter ratios this elemental fractionation must have happened long time ago to allow for radiogenic decay of the long lived isotopes of rb 87 and sm 147 the spread rsd in the initial sr and nd isotope compositions of the weathered samples reach a minimum value around 12 13 ga which we interpret as the timing of the peak weathering event which led to fractionation of the parent daughter ratios for nd isotopes the average epsilon nd 1 2 ga of the weathered samples coincides with the epsilon nd 1 2 ga of the unweathered rock the timing of the weathering event coincides with the timing of the breakup of the columbia supercontinent and follows wide spread alkaline volcanism in the indian subcontinent this is the first such attempt to determine the timing of a weathering event in rocks using long lived radioactive isotopes c 2016 elsevier b v all rights reserved

sedimentation cycles and their diagenesis on the slope of a miocene carbonate ramp bahamas odp leg 166 numerous small scale depositional cycles are present in the miocene sediments of seismic sequence m along the margin of great bahama bank odp leg 166 these cycles consist of decimetre to metre scale alternations between light grey and dark grey black wackestones packstones the light grey layers are well cemented and nearly uncompacted they contain planktonic and benthic foraminifera and bioclasts bioturbation in these layers is moderate the dark grey wackestones packstones are uncemented strongly compacted and normally strongly bioturbated the main components are planktonic foraminifera and fine grained bioclasts the dark layers are rich in aragonite and organic carbon and contain around 80 carbonate the light layers show low aragonite and organic carbon contents combined with carbonate values of up to 97 5 light 13c and slightly negative 18o values were observed in the dark uncemented layers while the cemented intervals show heavy 13c values and slightly more positive 18o values the carbon isotope signal between the dark and the light layers shows variations of up to 1 45 both 13c and 18o co vary with carbonate content the formation microscanner images reflect the changes in carbonate mineralogy the natural gamma ray tool shows that variations in siliciclastic content of the examined succession displays a different frequency than the cyclic alternations in carbonate mineralogy the internal stacking pattern of the cycles is closely tied to sea level the dark layers are deposited during rising sea level while the light layers reflect sediment production and export during highstand and falling sea level these cycles thus represent a rather continuous sediment shedding pattern that is clearly related to the ramp morphology and differs from the highstand shedding pattern typical for rimmed flat topped platforms most measured parameters suggest that primary sediment composition played an important role in the cementation process the primary differences in composition were enhanced during shallow burial diagenesis the initially high content of metastable carbonate phases in the periplatform sediments triggered rapid cementation of the primary aragonite rich layers leading to the formation of the light beds dissolution of metastable high mg calcite and aragonite was followed by in situ precipitation of more stable dolomite and calcite diagenesis was enhanced by the coarse grain size of the primary aragonite rich layers in contrast the more pelagic dark calcite rich layers were only slightly affected by diagenesis and could preserve their aragonite content the uncemented layers subsequently were subject to strong mechanical compaction whereas the cemented beds stayed nearly uncompacted

seismic source theory in stratified anisotropic media we extend seismic source theory to general anisotropic media for the numerical evaluation of spectral amplitudes of point sources in multilayered anisotropic crustal models first we obtain an explicit representation of the spectral elastodynamic green s tensor in general homogeneous anisotropic media as a sum of three integrals over the corresponding three slowness surfaces the multidimensional stationary phase principle is then applied to derive an asymptotic approximation at the far field in the case of azimuthally isotropic media we offer an alternative representation of the green s tensor and its ensuing displacements fields in the form of an exact hankel transform over the horizontal wave number variable the total field is specified here in terms of two potentials an sh potential and a mixed quasi transverse quasi longitudinal potential both of which assume the role of two scalar green s functions the availability of the green s tensor in analytical form enables one to obtain readily numerical solutions for a wide selection of media and sources it is shown that the radiation field of an explosion has the following new features 1 quasi transverse waves are created with four and eight lobe patterns 2 quasi longitudinal waves are generated for the collatitudinal displacement with four lobe patterns 3 the energy ratio sv p may reach the value of 20 for more than 50 of the azimuths in crustal structures such as tuff and shales and 4 radiation patterns for vertical shear waves are created which are indistinguishable from corresponding waves produced by earthquake faults our formalism allows us to establish a haskell type matrix algorithm for a multilayered azimuthally isotropic half space which enables us to calculate body waves and surface waves in real earth crustal models

on near source earthquake triggering 1 when one earthquake triggers others nearby what connects them two processes are observed static stress change from fault offset and dynamic stress changes from passing seismic waves in the near source region r 50 km for m 5 sources both processes may be operating and since both mechanisms are expected to raise earthquake rates it is difficult to isolate them we thus compare explosions with earthquakes because only earthquakes cause significant static stress changes we find that large explosions at the nevada test site do not trigger earthquakes at rates comparable to similar magnitude earthquakes surface waves are associated with regional and long range dynamic triggering but we note that surface waves with low enough frequency to penetrate to depths where most aftershocks of the 1992 m 5 7 little skull mountain main shock occurred 12 km would not have developed significant amplitude within a 50 km radius we therefore focus on the best candidate phases to cause local dynamic triggering direct waves that pass through observed near source aftershock clusters we examine these phases which arrived at the nearest 200 270 km broadband station before the surface wave train and could thus be isolated for study direct comparison of spectral amplitudes of presurface wave arrivals shows that m 5 explosions and earthquakes deliver the same peak dynamic stresses into the near source crust we conclude that a static stress change model can readily explain observed aftershock patterns whereas it is difficult to attribute near source triggering to a dynamic process because of the dearth of aftershocks near large explosions

marine carbonate factories a global model of carbonate platform distribution platform carbonates are a major component of the earth system but their spatial distribution through geological times is difficult to reconstruct due to the incompleteness of geological records sampling heterogeneity and their intrinsic complexity beyond this complexity carbonates are not randomly distributed in the world oceans neither in the modern nor in the past and thus global trends exist in the present review we focus on the understanding of the spatial distribution of carbonate production at a global scale we use a deterministic approach which focuses on discriminating components stratigraphic architectures and environmental features to relate shallow water carbonate production to oceanographic parameters the work is based on extensive literature reviews on carbonate platforms ecological niche modelling coupled with deep time general circulation models is used to calibrate a predictive tool of carbonate factory distribution a carbonate factory function is set up that is based on sea surface oceanographic parameters temperature salinity and primary productivity the model was tested using remote sensing and in situ oceanographic data of modern times while outputs of paleoceanographic models are utilized for lower aptian cretaceous modelling the approach allows determining four neritic carbonate factories that are called the marine biochemical photozoan photo c and heterozoan factories the model finely simulates the global distribution of lower aptian and modern carbonate platforms carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation this conceptual scheme appears to be able to provide a simple universal model of paleoclimatic zones of shallow water marine carbonates

propagation velocity of shockwaves and pressure waves in soil and rock a variable pressure wave propagation velocity is developed and analyzed in ground materials which may be characterized by an exponential density pressure relationship the peak overpressure dependence is minor in the low pressure range and the propagation velocity of the pressure wave is essentially a constant in fact it is the seismic p wave propagation velocity pressure dependence becomes increasingly more significant at peak overpressures exceeding 1 kbar 108 pa at very high pressure levels encountered only in shockwaves at and above 10 kbar 109 pa the initial mechanical characteristics of the ground materials become less significant and the propagation velocity depends primarily upon the peak overpressure

sediment characteristics in reef areas influenced by eutrophication related alterations of benthic communities and bioerosion processes abstract this study investigated sediment deposits and suspended particulate matter in three reef areas of reunion island characterized by varying benthic communities and bioerosion processes as a result of different eutrophication levels the sediments were sampled using two different methods hand collecting directly on the reef bottom and sampling by traps this approach allowed a comparison between the composition of reefal bottom sediments and suspended particles in locations where algal communities prevailed over corals as a result of nutrification a shift from coral to coralline algae dominated sediments could be observed in addition a decrease in sediment production and a prevalence of very fine sand to mud sized grains over medium to fine sands existed in the nutrient enriched areas this grain size difference probably is caused by a decrease in grazing activity in the enriched areas high proportions of coralline algal debris and sponge spicules were specifically found in the sediments within areas receiving high nutrient input these two diagnostic components were abundant in both the suspended particulate matter and in the fine fractions

two dimensional array measurements of near source ground accelerations abstract two dimensional array measurements of near source accelerations have been conducted 6 km from the 5 6 m l explosion colwick at pahute mesa nevada test site the three component nine station array measured 400 m across with interstation spacing of 100 m wavenumber spectra and beam forming stacking were used to measure apparent velocities and directions of propagation of acceleration waveforms the robustness of individual station accelerograms was measured with frequency domain coherency estimates and cross correlation functions the dependence of interstation coherency upon station spacing and frequency band was also examined wave propagation in pahute mesa can be characterized by p sv and sh wave motion in a horizontally homogeneous medium for frequencies below 5 hz strong incoherent scattered signals are present above 5 hz on all components the fraction of scattered energy can be estimated and treated as signal generated noise a strong sh pulse was observed to propagate across the array measured phase velocity arrival time and direction of propagation require cogeneration of sh with p sv energy by the explosion colwick weaker and more diffuse transverse acceleration signals arrive coincident with the p wave and during the time prior to s these arrivals are interpreted as forward scattered energy from the p wave the small array permitted a refinement of the horizontally averaged s wave velocity model for pahute mesa the mesa is characterized by a low velocity layer 600 m thick above the water table with a steep velocity gradient immediately below the coherency measurements indicate the upper 1 km or more of pahute mesa is heterogeneous at scale lengths less than 1 km

tracing the source of sediment and phosphorus into the great barrier reef lagoon neodymium and strontium isotopic systematics show that terrestrial phosphorus p entering the inner great barrier reef gbr is dominated by the transport and dispersal of fine grained basaltic soils soils derived from alkali basalts have high total p 3000 4000 mg kg and distinctive 143 nd 144 nd isotopic signatures ondv 3 to 5 while the more common palaeozoic granitic metamorphic soils have much lower total p 300 600 mg kg and 143 nd isotopic signatures ondv38 the nearshore environment 6 5 km from the coast is dominated by coarse grained graniticderived fluvial detritus while s 20 km from the coast carbonate rich sediments with increasing contributions from basaltic components become more important in the offshore sites adjacent to coral reefs it is shown that basaltderived sediments can account for s 90 of the terrestrial p although making up less than half of the total terrigenous detritus equilibrium phosphorus concentration measurements on the marine sediments indicate that p enters the gbr lagoon via a two stage process firstly during episodic flood events p is transported into the gbr lagoon on p retentive fine grained suspended sediments with only minor desorption of p occurring in the low salinity flood plumes desorption of p mainly occurs over longer timescales predominantly in regions of sediment anoxia with release of po 33 4 directly into marine pore waters probably via reduction of ferric phosphates and subsequent release into the water column by re suspension this process causes p depletion of the re deposited sediments 2003 elsevier science b v all rights reserved

a source model for induced earthquakes at the geysers geothermal reservoir the results of a previous study on source mechanisms of small earthquakes at the geysers geothermal reservoir in northern california are used to investigate an extended crack model for seismic events the seismic events are characterized by their first degree moment tensors and interpreted in terms of a model that is a combination of a shear crack and wing cracks solutions to both forward and inverse problems are obtained that can be used with either dynamic or static moment tensors the model contains failure criteria explains isotropic parts that are commonly observed in induced earthquakes and produces estimates of crack dimensions and maximum amount of slip effects of fluid pressure are easily incorporated into the model as an effective stress the model is applied to static moment tensors of 20 earthquakes that occurred during a controlled injection project in the northwest geysers for earthquakes in the moment magnitude range of 0 9 2 8 the model predicts shear crack radii in the range of 10 150 m wing crack lengths in the range of 2 25 m and maximum slips in the range of 0 3 1 1 cm only limited results are obtained for the time dependence of the earthquake process but the model is consistent with corner frequencies of the isotropic part of the moment tensor being greater than the deviatoric part and waveforms of direct p waves that become more emergent for larger events

lg coda methods applied to nevada test site events spectral peaking and yield estimation abstract we have applied the regional s wave coda calibration technique of mayeda et al 2003 to earthquake data in and around the nevada test site nts using four regional broadband stations from the lawrence livermore national laboratory llnl seismic network we applied the same path and site corrections to tamped nuclear explosion data and averaged the source spectra over the four stations narrowband coda amplitudes from the spectra were then regressed against inferred yield based on the regional m b pn magnitude of denny et al 1987 along with the yield formulation of vergino and mensing 1990 we find the following 1 the coda derived spectra show a peak that is dependent upon emplacement depth not event size 2 source size estimates are stable for the coda and show a dependence upon the near source strength and gas porosity 3 for explosions with the same m b pn or inferred yield those in weaker material have lower coda amplitudes at 1 3 hz

two sources of nonisotropic radiation from underground explosions in granite significant tangential ground motion observed during underground explosions makes it difficult to distinguish them from natural earthquakes such motion can be generated by the source geometry and emplacement conditions by the heterogeneous nature of the rock mass mechanical properties may vary in space due to the presence of cracks joints faults and various geologic layers and also by the nonuniform in situ stress state the last mechanism is increasingly important with depth when the difference in main principal stresses becomes significant this paper is focused on the role of material strength of the rock mass in generation of non radial motion during explosions in pre stressed media numerical modeling of underground chemical explosions in granite at various depths have been conducted to compare two possible mechanisms of shear wave generation the first caused by rock mass anisotropy is important at shallow depth the second is related to elastic plastic relaxation around the cavity created by the explosion tangential motions for these two mechanisms have different signatures