the physical basis of mb ms and variable frequency magnitude methods for earthquake explosion discrimination we use recent results from deterministic numerical modeling of earthquakes and explosions to develop an improved physical basis for earthquake explosion discrimination we use six three dimensional finite difference simulations of earthquakes for the earthquake source models and four empirical and four numerical models for explosions in different materials four factors contribute to the success of the mb ms discriminant source spectra focal mechanism near source elastic properties and interference of p spectral differences contribute about 0 5 magnitude unit to the separation between earthquake and explosion populations for large events but this difference vanishes for events with mb 4 0 using a frequency band of 0 5 3 0 hz for small events the vfm discriminant is complementary to mb ms in several ways vfm is improved by p interference while mb ms is degraded vfm is more effective for hard rock explosions while mb ms will preferentially discriminate explosions in low velocity materials and vfm is insensitive to fault orientation vfm is more sensitive to noise and regional attenuation differences than mb ms simultaneous use of both methods should allow improved discrimination of small events

discriminating between large mine collapses and explosions using teleseismic p waves some of the most suspicious seismic disturbances under the comprehensive nuclear test ban treaty ctbt are likely to be those associated with mining as they are shallow and at least some have an explosion like m b m s signature previous research highlighted the potential of broadband teleseismic p waves as a way of identifying large mine tremors broadband teleseismic p from two suspected large mine collapses one in germany 1302 ut 13 march 1989 5 4 m b and another in wyoming 1526 ut 3 february 1995 5 3 m b show differences in character despite the similarity of the reported ground failure and mine types we apply a full moment tensor analysis to the teleseismic p waves and show that the data are inconsistent with either a shallow explosion or an earthquake double couple at depth but this method is unable to distinguish between a shallow dip slip source and a closing crack moment tensor however three component surface wave seismograms recorded at regional distances fit the shallow closing crack model but are inconsistent with a shallow earthquake source because strong love waves expected from a double couple source are not observed at a number of stations well distributed in azimuth here we restate the equivalence for shallow sources of the closing crack model and a gravitational collapse model we use the latter to model the broadband p waves from these mine tremors and show that while non unique the differences in the observed broadband p waves from the two tremors can be attributed to the area amount of collapse depth and rate of collapse the collapse model predicts negative first motion for all p waves in contrast to the positive polarity expected from explosions thus the broadband teleseismic p waves have the potential to discriminate between large collapses and explosions

analysis of local seismic waveforms from underground nuclear explosions forward modeling for effective source functions at pahute mesa in this study we use forward modeling of surface particle velocity data recorded within 15 km of underground nuclear explosions at pahute mesa in the nevada test site a plane layered velocity structure model is developed and effective source functions are obtained for six events with yields of 155 1300 kt kilotons recorded at ranges presumed to be well outside the zone of inelastic deformation we then use the effective source functions determined from well outside the elastic radius to compute synthetic seismograms for comparison with recordings within the spall zone prior to the onset of spall the comparison is good enabling us to estimate effective source functions for two additional events for which only recordings from the spall zone are available as surface zero is approached however the first half cycle of the observed velocity records includes an inflection which appears as a shoulder in acceleration records this suggests that in addition to the elastic arrival we are seeing secondary arrivals due to spall opening or inelastic shock wave propagation elastic wave propagation predicts the observed peak velocities well beyond a scaled slant range of about 175 m kt but overpredicts the first phase at closer ranges this limit of applicability of elastic wave propagation provides a useful estimate of the elastic radius for pahute mesa explosions yield scaling relations are determined using three events of known yield and these are then used to estimate yields for the eight pahute mesa explosions modeled in this study finally implications for the attenuation of teleseismic body waves are discussed

spectral discrimination between nts explosions and western united states earthquakes at regional distances spectral ratio disciminants are applied to 72 western united states earthquakes and 64 nts explosions recorded at four broadband seismic stations surrounding nts the ratio of the energy in the 1 to 2 and 6 to 8 hz bands for pn pg and lg is calculated and a simple distance correction applied to the data the spectral ratio appears to have potential as a disciminant at relatively small magnitudes 3 0 4 5 to 5 0 this may be due to uncertainties in the apparent source time function for explosions these complications may be due to changes in the dynamic response of the material in the near source region as a function of overburden pressure effects of secondary sources or to variations in regional phase excitation with depth

effects of source rdp models and near source propagation implication for seismic yield estimation ithas proven difficult to uniquely untangle the source and propagation effects on the observed seismic data from underground nuclear explosions even when large quantities of near source broadband data are available for analysis this leads to uncertainties in our ability to quantify the nuclear seismic source function and consequently the accuracy of seismic yield estimates for underground explosions extensive deterministic modeling analyses of the seismic data recorded from underground explosions at a variety of test sites have been conducted over the years and the results of these studies suggest that variations in the seismic source characteristics between test sites may be contributing to the observed differences in the magnitude yield relations applicable at those sites this contributes to our uncertainty in the determination of seismic yield estimates for explosions at previously uncalibrated test sites in this paper we review issues involving the relationship of nevada test site nts source scaling laws to those at other sites the joint verification experiment jve indicates that a magnitude m b bias 6m b exists between the semipalatinsk test site sts in the former soviet union fsu and the nevada test site nts in the united states generally thissmbis attributed to differential attenuation in the upper mantle beneath the two test sites this assumption results in rather large estimates of yield for largem b tunnel shots at novaya zemlya a re examination of the us testing experiments suggests that thissm b bias can partly be explained by anomalous nts pahute source characteristics this interpretation is based on the modeling of us events at a number of test sites using a modified haskell source description we investigated the influence of the source reduced displacement potential rdp parameters lkand bby fitting short and long period data simultaneously including the near field body and surface waves in general estimates of band kare based on the initial p wave pulse which various numerical analyses show to be least affected by variations in near source path effects the corner frequency parameter kis 20 lower at nts pahute than at other sites implying larger effective source radii the overshoot parameter bappears to be low at nts although variable relative to other sites and is probably due to variations in source conditions for a low b the near field data require a higher value of to match the long period m s and short periodmbobservations this flexibility in modeling proves useful in comparing released fsu yields against predictions based onm b andm s

constraints on burial depth and yield of the 25 may 2009 north korean test from hydrodynamic simulations in a granite medium 1 yield depth of burial dob tradeoff curves tocs based on seismic magnitudes of the 25 may 2009 north korean test depend strongly on the choice of empirical cavity radius rc scaling model ambiguities over rc scaling particularly at large scaled dob sdob translate into unacceptably large systematic errors on yield estimates for this test hydrodynamic calculations involving realistic material response models offer a viable alternative to characterize rc scaling for a range of sdob where limited data from past nuclear tests exist results of such calculations are presented for a granite medium with a material response validated by modeling four phenomenological criteria for past nuclear tests in granite free field velocity energy partitioning into the seismic wavefield velocity attenuation and measured rc these results unambiguously favor the rc scaling model of denny and johnson dj91 and the toc based on that model lower bounds on yield and dob of the north korean test are constrained by predictions of an sdob threshold for free surface damage from 2 d simulations since no such reported damage was observed for this test constrained by the hydrodynamic simulations the dj91 model indicates the minimum yield and dob for the 25 may 2009 north korean test is 5 7 kilotons and 375 m

induced seismicity of the groningen gas field history and recent developments abstract induced seismicity of the groningen gas field is caused by the production of gas because of the large areal extent of the reservoir the long history of depletion and the available data sets which exist as a result of consequences and public unrest caused by induced seismicity the field presents a valuable case for studying the relationships among geologic flow dynamic geomechanical and seismological models gas production from the groningen field started in 1963 induced seismicity of the field first was recorded in 1991 ml 2 4 during the subsequent 10 years induced seismicity stayed at a rate of about five events ml 1 5 per year starting in 2003 the number of events and magnitudes started to increase in 2012 the largest event ml 3 6 occurred which caused the most damage to date as a consequence studies carried out in 2013 have fundamentally changed the way to look at the relationship between induced seismicity and gas depletion there appears to be a close link between

a method for computing infiltration and redistribution in a discretized moisture content domain 1 a new one dimensional infiltration and redistribution method is proposed as an alternative to the richards equation re for coupled surface and subsurface models the proposed method discretizes soil water content into hypothetical hydraulically interacting bins the entry and propagation of displacement fronts in each bin are simulated by means of explicit infiltration and drainage approximations based on capillary and gravitational driving forces wetting front advances within bins create water deficits that are satisfied by capillary driven interbin flow the method inherently provides numerical stability by precluding the need to directly estimate nonlinear gradients through numerical schemes comparisons of the performance of this method against re solutions for theoretical laboratory and field data in both well drained and high water table conditions are presented the new method produces infiltration flux estimates with errors less than 10 compared to a widely used re solution in tests on multiple soil textures with and without high water table conditions while providing unconditionally guaranteed conservation of mass

constraints on explosive sources with spall from near source waveforms spall the tensile failure of a material due to high stress loading has been observed in a number of contained and surface explosions the phenomenon results in a repartition of the initial spherical explosion energy source yielding a second energy source which is cylindrical and delayed in time recent spall models by day et al 1983 demanding conservation of momentum have shown the phenomenon to have little contribution to 20 sec surface waves these models are extended to include the effect of the process on near source seismograms the spall model is constrained by observations within the nonlinear regime of the source which bound the mass momentum and timing of the process comparison of these forward models with the inverse vertical point force source inferred from seismic recordings of a bermed surface explosion yields excellent agreement the spall model developed from the contained explosion cheat is used to create synthetic seismograms comparisons of these waveforms with those from a mueller murphy contained explosion indicate that the waveform contribution from spall is similar in size to the spherical explosion waveform the complete synthetic composed of the spall and explosion contribution compares favorably with observational data from the cheat experiment in both amplitude and energy distribution

moving multi front mmf a generalized green ampt approach for vertical unsaturated flows abstract a moving multi front mmf method is developed and tested for solving the richards equation governing unsaturated flow in vertical homogeneous porous columns the mmf model is a gridless method it can be viewed as a generalization of the green ampt piston flow approach which models flow as a single abrupt moving front separating saturated and dry regions during infiltration the mmf model further generalizes this concept using a parametrization of unsaturated water retention and conductivity pressure curves it reduces the richards pde to an ode system governing m moving front positions different tests are developed to validate this approach for 1d transient downwards upwards flows submitted to constant and time varying pressure boundary conditions they include i infiltration to deep water tables ii infiltration to shallow water tables iii capillary rise from fixed water tables iv gradual water table rise partially saturated column with evolving pressure condition at bottom the mmf results are compared favorably to finely discretized fixed grid solutions of richards pde analyses of error and accuracy show satisfactory results in terms of water content profiles and boundary fluxes e g infiltration rate

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

probing the core mantle boundary beneath europe and western eurasia a detailed study using pcp summary we use pcp the core reflected p phase recordings of deep earthquakes and nuclear explosions from the grafenberg germany and norsar norway arrays to investigate the core mantle boundary region beneath europe and western eurasia we find evidence for a previously unknown ultra low velocity zone 600 km south east of moscow located at the edge of a middle size low shear velocity region imaged in seismic tomography that is located beneath the volga river region the observed amplitude variations of pcp can be modelled by velocity reductions of p and s waves of 5 and 15 respectively with a density increase of 15 travel time delays of pre and postcursors are indicating a thickness of about 13 km for this ultra low velocity region ulvz however our modelling also reveals highly ambiguous amplitude variations of pcp and a reflection off the top of the anomaly for various ulvzs and topography models accordingly large velocity contrasts of up to 10 in vp and 20 in vs cannot be excluded in general the whole volga river region shows a complex pattern of pcp amplitudes caused most likely by cmb undulations further pcp probes beneath paris kiev and northern italy indicate likely normal cmb conditions whereas the samples below finland and the hungary slovakia border yield strongly amplified pcp signals suggesting strong cmb topography effects we evaluate the amplitude behaviour of pcp as a function of distance and several ulvz models using the 1d reflectivity and the 2d gauss beam method the influence of the velocity and density perturbations is analysed as well as the anomaly thickness the dominant period of the source wavelet and interface topographies strong variation of the pcp amplitude are obtained as a function of distance and of the impedance contrast we also consider two types of topographies undulations atop the cmb in the presence of flat ulvzs and vice versa where a broad range of cmb topography dimensions lead to large pcp amplitude variations only large ulvz undulations generate significant amplitude scattering consequently this indicates that topography effects of anomalies may mask the true medium parameters as well as the ulvz thickness moreover there might be a possibility of misinterpreting the precursor as pcp in particular for thin ulvzs

mitigating induced seismicity around depleted gas fields based on geomechanical modeling mitigation of induced seismicity associated with large scale energy production from subsurface resources requires models beyond the current state of the art in countries with long histories of conventional gas production such as the netherlands issues are mainly associated with depletion induced seismicity caused by fault reactivation due to differential compaction of reservoir compartments that are juxtaposed at faults geomechanical modeling approaches can be extended and integrated to better assess the occurrence of depletion induced seismicity and provide a basis to modify operations with the aim of mitigating seismicity static models of fault stability and reactivation can be used to analyze the location and likelihood of fault reactivation during injection or depletion operations dynamic models of fault rupture and seismic wave propagation can be used to analyze the characteristics of induced seismicity from seismic source to expressions motions at surface or potential sensor locations ensemble based optimization workflows can be used to maximize production under constraints imposed by thresholds for induced seismicity the combination of these modeling approaches can be used to determine fault sections that are most prone to induce seismicity analyze the fault rupture process and associated characteristics of induced seismicity and optimize well production strategies for minimizing induced seismicity integrated geomechanical modeling of depletion induced seismicity and production optimization workflows can lead to gas production strategies that maximize total gas production while minimizing seismic risk 2018 by the society of exploration geophysicists

near source effects on regional seismograms an analysis of the nts explosions pera and queso a comparative analysis of two closely spaced nevada test site explosions pera and queso is made to study the effects of near source phenomena on regional wave excitation although the two explosions were of similar size burial depth and only separated by 4 km the 1 to 2 and 6 to 8 hz regional wave spectral ratio for queso is anomalously low a factor of 10 smaller than that of pera examination of the regional and close in spectra for each event shows a remarkable similarity and suggests that queso has less low frequency and more high frequency energy than pera these observations may be caused by a 564 m3 funnel shaped region filled with unconsolidated sand and a possible void directly above the queso detonation point close in observations suggest that this region may have partially decoupled the up going energy from queso resulting in a reduction of the low frequency energy the high frequency enhancement for queso may be due to the rapid loss of energy to nonlinear effects such as greater pore collapse and fracturing in the anomalous region this resulted in the radiation of more impulsive shorter duration waveforms producing a higher corner frequency and less rapid high frequency spectral decay for queso for pera the loss of energy to a two wave system occurred more slowly and over a larger volume resulting in a broader source pulse typical of explosions in porous materials comparison of shock radius versus time data suggests that the shock wave was strongly affected in the anomalous zone a few meters above the queso device one dimensional finite difference calculations with and without a partial decoupling region within 8 m of the device are consistent with the observations although spallation was reduced for queso simulations using a finite spall model indicate that the spall spectral peak should be centered at about 3 to 7 hz and probably did not significantly contribute to the reduced spectral ratio the remarkable similarity of the pera queso spectral ratios taken at distances of 90 m and 400 km suggests that the spectral characteristics of explosions are established in close proximity to the source although depth dependent effects of attenuation acting at small strains may enhance the differences in spectral ratios between nts explosions and western u s earthquakes these effects are probably secondary to the high pressure high strain rate dynamic material response to the radiated explosion shock wave these observations point out the importance of up going energy on the generation of regional phases from explosions because of reduced overburden pressures above the detonation point large nonlinear deformations predominate in this region and appear to affect all of the signals except perhaps the very initial part of the pn waveform

understanding induced seismicity fluid injection induced seismicity has become increasingly widespread in oil and gas producing areas of the united states 1 3 and western canada it has shelved deep geothermal energy projects in switzerland and the united states 4 and its effects are especially acute in oklahoma where seismic hazard is now approaching the tectonic levels of parts of california unclear in the highly charged debate over expansion of shale gas recovery has been the role of hydraulic fracturing fracking in causing increased levels of induced seismicity opponents to shale gas development have vilified fracking as directly responsible for this increase in seismicity however this purported causal link is not substantiated the predominant view is that triggering in the midwestern united states is principally a result of massive reinjection of energy coproduced wastewaters on page 1406 of this issue bao and eaton 5 identify at least one example of seismicity developed from hydraulic fracturing for shale gas in the alberta basin

characterization of spall from observed strong ground motions on pahute mesa abstract ground motion velocity and acceleration data recorded within the spall region on over 30 pahute mesa explosions have been analyzed for characterization of the spall source these data provide observations of peak spall velocities and the spatial extent of spall from which estimates of the volume and mass of spalled material were obtained along with the yield scaling spall velocities at ground zero are higher and the apparent attenuation of velocities is lower for explosions below the water table compared to shots above the water table in tuff or rhyolite as a result the lateral and depth extents of spall are larger for shots below the water table and the estimated spall mass is three times larger than the estimate for explosions above the water table the lateral and depth extents were found to scale as the quarter root of the yield w as opposed to the familiar cube root scaling and assuming a cylindrically symmetric volume the mass scales as w 0 77 05 at 150 kt the estimated mass for a shot below the water table is 15 times greater than the first estimates made by viecelli while this estimate suggests a much larger spall source than originally believed not all of the mass is necessarily involved in generating seismic waves recorded in the far field and the coupling efficiency of spall remains an outstanding unresolved problem

source characteristics of two underground nuclear explosions summary broadband seismic waveform data recorded in the distance range of 1 11 km from two underground explosions detonated at pahute mesa of the nevada test site have been used to estimate the source time functions for the second order moment tensors of these events data were available from eight three component stations for the explosion harzer and from 11 stations for the explosion chancellor stable moment tensor estimates with a good signal to noise ratio were obtained in the frequency range of 0 2 5 0 hz the moment tensors are dominated by the diagonal elements but a significant asymmetry is present with vertical force couples being larger having additional low frequency energy in the 0 3 0 4 hz range and having a different time dependence in the 0 5 2 5s range than the horizontal force couples considerable evidence points to the possibility that this asymmetry is related to spall processes taking place in the depth interval between the explosion and the free surface when the isotropic parts of the moment tensors are interpreted as reduced displacement potentials the results are in reasonable agreement with theoretical and empirical models except that the characteristic times are about three times those predicted by published scaling relationships this difference is most likely due to the effects of spall but the fact that the explosions were detonated in unsaturated materials may also be a contributing factor

green and ampt infiltration into soils of variable pore size with depth most expressions for infiltration rely upon the assumption of vertical uniformity in soil texture and hydraulic properties we present an extension of the results of beven 1982 1984 for infiltration and lateral flow in soils with decreasing permeability with depth unlike beven we base the derivations upon joint changes in soil properties based on an overall change in characteristic pore size via miller scaling a set of very simple expressions for the time rate of infiltration are obtained using a green and ampt approach for soils with permeability that decreases with depth following linear power law and exponential relationships

the pwaves from the amchitka island explosions summary there is evidence that the equivalent seismic sources of the amchitka island explosions longshot milrow and cannikin depart significantly from the simple model of a point compressional source in a layered elastic medium consequently modelling the observed seismograms using standard source models may not be the most efficient method of determining source properties here an alternative to modelling is used to obtain information on the seismic sources due to the explosions broad band bb estimates of the p signals are obtained from the short period sp seismograms corrected for attenuation and interpreted in terms of p pp and radiation from secondary sources the main conclusions are i bb estimates of the radiated displacement from the explosions can be obtained with only a small reduction in the signal to noise ratio seen on sp seismograms ii observations of differences in pulse amplitudes and spectra are not necessarily due to differences in anelastic attenuation iii p and pp at a given station may differ in shape so that notches in the signal spectrum may not be related to source depth iv there is evidence of arrivals that others have identified as due to slapdown but which could be interpreted as an overshoot to pp v direct interpretation of the estimated ground displacement is a better procedure for determining the seismic source properties of explosions than modelling sp seismograms using idealised models as a starting point

frequency domain scaling of single fired mining explosions with different confinements and explosive weights detonated in porphyry granite abstract a series of single fired simultaneously detonated explosions were conducted in an arizona copper mine the explosions spanned yields from 773 to 6182 kg and were all detonated in an approximately 100 by 100 m area the individual explosions were also detonated under three different emplacement conditions including at the free face of the mine under normal burden distance from the free face resulting in failure and movement of the free face at twice normal burden with free surface failure and cratering and at twice normal depth which fully contained the explosions the purpose of this analysis was to investigate the relationship between explosive weight and confinement on the amplitude and frequency content of seismic waves empirical scaling relations for the different shots in this test series were developed using common receivers in order to quantify the effects of explosive weight and confinement spectral ratios between observations at the same stations for the different explosions were used to remove common instrument and propagation path effects from the data set empirical scaling functions estimated from data at ranges from a few hundred meters to several tens of kilometers produce similar results the mueller murphy source model has been used to assess the effects of explosion depth and material in which the explosions are detonated material properties were measured for the porphyry granite at the mine and were used in forward models for the yield scaling of the fully contained explosions the forward models replicate the empirical scaling functions at low frequency

source time functions of nuclear explosions and earthquakes in central asia determined using empirical green s functions relative source time functions rstf have been estimated for four underground nuclear explosions and seven earthquakes in central asia using broadband p waveforms of nearby smaller events as empirical green s functions egf rstfs of the four explosions m sub b 5 3 to 6 5 are each dominated by a simple pulse with a source duration of 0 4 to 0 8 s rstfs for two of the explosions show a significant secondary pulse with a pulse width similar to that of the first pulse the authors conclude that the secondary phases are most likely associated with the spall slapdown phenomenon seismic moment releases by the spall phases are less than one third of those by the first explosion pulses elastic radii of the explosions are estimated to be about 0 25 to 0 5 km and stress drops of the explosion range from 13 to 52 mpa in contrast rstfs of earthquakes studied m sub b 5 5 to 6 6 typically comprise multiple source pulses with a total source duration from a few to several tens of seconds indication that the complex source process involves a fault dimension of several tens of kilometers stress drops of the earthquakes are much smaller than those of the nuclearmore explosions ranging from 0 5 to 3 5 mpa the authors study demonstrates the power of the egf method for retrieving rstfs and reveals that differences in rstfs and source parameters can be used to distinguish large nuclear explosions from moderate to large earthquakes m sub b 5 5 80 refs 11 figs 6 tabs less

tectonic release from the soviet joint verification experiment the regional broadband seismic recordings of the soviet joint verification experiment underground nuclear explosion show evidence of tectonic release in the form of love waves at long periods and high frequency s sub m s phases on the transverse components the authors present the results of some simple forward modeling of this data in order to quantify both the moment and mechanism of the tectonic release using 10 20 second love wave amplitude and phase data they estimate the tectonic release moments to be 3 5 times 10 sup 15 n m for a north striking right lateral strike slip fault and 7 0 times 10 sup 15 n m for a northwest striking reverse fault using the results of these end member tectonic models the rayleigh waves can be satisfied with explosion moments of 1 7 times 10 sup 16 n m f 0 31 and 2 4 times 10 sup 16 n m f 0 44 respectively to resolve the ambiguity in tectonic mechanism the authors used the reflectivity method to generate synthetics and compare the relative amplitudes of the sh and sv parts of the s sub m s phase while the results favor the strike slip mechanism of tectonic release application of source inversion techniques to this data and other regional data will be needed to evaluate more realistic tectonic releasemore models involving for example oblique fault slip and dip less

the effects of spall on regional seismograms the effects of spall on regional signals are investigated using synthetic seismograms to frequencies of 20 hz depending on the scaling relationships used it is found that spall may have an important effect on regional body waves and especially surface waves the frequency range in which the spall effect dominates is dependent upon the characteristic times of the spallation process but generally occurs in the frequency range of about 0 2 to 2 hz because of the peaked nature of the radiated spall spectra effects at frequencies outside the 0 2 to 2 hz frequency range will be dominated by the explosion source the frequency range and strength of the spall effect depend in a complicated manner upon the yield depth of burial near source structure and material strength uncertainties in the spall scaling relationships need to be better understood before the effects of spall on regional discrimination and yield estimation can be properly quantified copyright american geophysical union 1989

ml m0 as a regional seismic discriminant the m b m s ratio determined by teleseismic observations has proven to be an effective discriminant for explosive sources tend to be significantly richer in short period energy than are earthquakes unfortunately this method is limited by the detection threshold of teleseismic surface waves however recent advances in instrumentation allowing low amplitude surface wave measurements coupled with new analytical techniques make it feasible to use regional waveform data to determine the long period source excitation level of low magnitude events we propose using the ratio of m l local magnitude to m 0 scalar seismic moment as an analogous regional discriminant we applied this criterion to a data set of 299 earthquakes and 178 explosions and found that this ratio seems to be diagnostic of source type for a given m 0 the m l of an explosion is more than 0 5 magnitude units larger than that of an earthquake this separation of populations with respect to source type can be attributed to the fact that m l is a short period 1 hz energy measurement whereas seismic moment is determined from long period body wave phases period 4 s and surface waves 10 to 40 sec using regional stations with sources 200 to 600 km away the effective threshold for magnitude measurements for this discriminant is found to be m l 3 1 for earthquakes and m l 3 6 for explosions this method does require the determination of regional crustal models and path calibrations from master events or by other means

surface waves from underground explosions with spall analysis of elastic and nonlinear source models anomalous surface wave observations from underground explosions have been widely attributed to the phenomenon of spall i e the detachment and subsequent slapdown of near surface layers in response to explosion induced tensile stresses we argue on the basis of a simple equivalent force model that while spall can enhance explosion surface waves at very short periods it cannot contribute significantly to the teleseismic surface waves radiated by underground explosions at periods exceeding about 10 sec previous theoretical results to the contrary are in error having been based on source models which do not conserve momentum a nonlinear two dimensional axisymmetric finite difference simulation of a buried explosion in granite further supports the conclusion that spall cannot contribute to long period surface waves the simulation exhibits extensive spall nonetheless predicted fundamental mode rayleigh wave spectra are nearly identical to those obtained from a spherically symmetric simulation which does not include spall at periods exceeding about 10 sec at shorter periods the two dimensional simulation predicts some rayleigh wave enhancement compared to the one dimensional simulation the maximum enhancement about a factor of 2 occurs at a period of approximately 2 5 sec synthetic long period rayleigh wave seismograms at 3000 km range show no perceptible phase or amplitude anomalies due to spall these results are in excellent agreement with the predictions of our equivalent force model

false alarms and mine seismicity an example from the gentry mountain mining region utah as part of a large discrimination study in the western united states taylor et al 1989 one earthquake was consistently classified as an explosion the magnitude m 3 5 disturbance occurred on 14 may 1981 and was conspicuous in its lack of love waves relative lack of high frequency energy low lg pg ratio and high moment tensor additionally a moment tensor solution by patton and zandt 1991 indicated that the event had a large implosional component the event occurred in the gentry mountain coal mining region in the eastern wasatch plateau utah previous microearthquake studies in the region have demonstrated the existence of numerous small implosional events associated with the mining activities the event is more comparable in appearance at the broadband station at kanab utah knb to the atrisco collapse at the nevada test site nts than to another double couple event near the mining region using a simple source representation we modeled the event as a tabular excavation collapse that occurred as a result of normal mining activities this study raises the importance of having a good catalog of seismic data and information about mining activities from potential proliferant nations this information will be critical in resolving potential false alarms that may be generated from natural mine seismicity

empirical and numerical modeling of t phase propagation from ocean to land t phase propagation from ocean onto land is investigated by comparing data from hydrophones in the water column with data from the same events recorded on island and coastal seismometers several events located on hawaii and the emerging seamount loihi generated very large amplitude t phases that were recorded at both the preliminary ims hydrophone station at point sur and land based stations along the northern california coast we use data from seismic stations operated by u c berkeley along the coast of california and from the pg e coastal california seismic network to estimate the t phase transfer functions the transfer function and predicted signal from the loihi events are modeled with a composite technique using normal mode based numerical propagation codes to calculate the hydroacoustic pressure field and an elastic finite difference code to calculate the seismic propagation to land based stations the modal code is used to calculate the acoustic pressure and particle velocity fields in the ocean off the california coast which is used as input to the finite difference code tres to model propagation onto land we find both empirically and in the calculations that t phases observed near the conversion point consist primarily of surface waves although the t phases propagate as p waves after the surface waves attenuate surface wave conversion occurs farther offshore and over a longer region than body wave conversion which has the effect that surface waves may arrive at coastal stations before body waves we also look at the nature of t phases after conversion from ocean to land by examining far inland t phases we find that t phases propagate primarily as p waves once they are well inland from the coast and can be observed in some cases hundreds of kilometers inland t phase conversion attenuates higher frequencies however we find that high frequency energy from underwater explosion sources can still be observed at t phase stations

anatomy of regional phases and source characterization of the soviet joint verification experiment underground nuclear explosion broadband data from the nrdc deployment of stations in kazakhstan at karkaralinsk kkl and bayanual bay are subjected to detailed waveform modeling to understand the nature of regional wave propagation and to determine the nature of the explosion time function and sources of low and high frequency tectonic release minor modification of a crustal model inferred from dss studies in the region is very effective in explaining the arrival times amplitudes and waveshapes of the pn and pmp arrivals at both stations the sh wave data are remarkable however for showing a large high frequency arrival after the expected and observed arrival of sms from the explosion source these secondary s arrivals imply a secondary source 1 to a few kilometers to the south of the shot point shear waves from this source dominate the seismic data at high frequency but are minor at low frequency where shear waves and surface waves from the inferred relaxation of the explosion cavity dominate the wave field the secondary s wave source is inferred to represent explosion driven faulting with no net moment significant overshoot in the rdp is required to match the p wave data it is found that von seggern blandford and haskell source functions are incapable of producing the observed overshoot however the mueller murphy source model is very effective in matching the clear overshoot effects seen in the p waves spall effects are also considered but appear to be minor and serve to require even more overshoot in the rdp the excitation and dispersion of rayleigh waves in the period band of 1 to 10 sec is seen to be a sensitive but nonunique function of both vs and vp in the upper crustal layer high poisson ratios in this layer are needed to explain the rayleigh waveform

variability in explosion body wave magnitudes an analysis of the rulison gasbuggy anomaly an analysis of the rulison gasbuggy mb anomaly is presented which encompasses comparative studies of near regional regional and teleseismic data recorded from these two explosions as well as theoretical simulation analyses of selected near regional and teleseismic data sets previously proposed explanations for this mb anomaly such as differences in explosive source coupling and variations in upper mantle attenuation beneath the two test sites are critically examined and shown to be inconsistent with various aspects of the observed data however both long period and short period evidence is presented which indicates that significant tectonic release accompanied the rulison explosion it is demonstrated that the short period near regional sh observations from rulison can be theoretically explained by an explosion induced tectonic release equivalent to a 250 to 300 bar stress drop at the elastic radius of the explosion the inferred prestress field is homogeneous to first order and oriented as a pure shear on planes dipping at about 45 with normal or dip slip displacements occurring as a consequence of stress relaxation such a tectonic release mechanism would be expected to decrease the associated explosion mb value by more than 0 3 units and therefore can provide a quantitative explanation of the observed rulison gasbuggy mb anomaly we conclude that tectonic release can significantly affect the short period teleseismic p waves from explosions at least in cases where the tectonic stress is large and favorably oriented

decomposition of seismic moment tensors for underground nuclear explosions generally the decomposition of a seismic moment tensor is not unique however to favorably view the characteristics of a certain seismic source one must decompose a seismic moment tensor into parts according to assumptions about the properties of the seismic source different from natural earthquakes in which the shear dislocation component plays a predominant role in the source process and the seismic moment tensor can be separated into an isotropic component a double couple and a compensated linear vector dipole clvd underground nuclear explosions have three major components in their source process i e the explosion the tensional spalling and the tectonic strain release associated with the explosion in such a situation the conventional moment tensor decomposition for earthquakes is not convenient to estimate the yield of the explosion and to characterize the tectonic strain release in this paper an alternative decomposition scheme is proposed to deal with the moment tensor of underground nuclear explosions which might benefit the approach to study the tectonic strain release induced by underground nuclear detonations

quantification and characterization of regional seismic signals from cast blasting in mines a linear elastic model summary cast blasts in coal mines designed to move large volumes of overburden are a source of large 1 5 kt frequent explosions in parts of the world with near surface coal resources mining events of this source type are triggering the prototype international monitoring system for the comprehensive test ban treaty being tested under the group of scientific experts technical test 3 gsett 3 we wish to develop techniques to distinguish between the seismic signals produced by these explosions and equivalent size single or point sources to that end we have developed a linear elastic model to simulate regional distance seismograms from mining cast blasts cast blasting involves a shot array with delayed detonations casting rock horizontally into a pit we model the effects of the millisecond delay firing pattern the depth of the pit and the cast of material into the pit we attempt to separate the effects due to the explosion the vertical movement of mass and the horizontal movement of mass in order to produce a physical understanding of the resulting waveforms which can be used to assess potential discriminants for these types of explosions these physical models of source processes are constrained by near surface measurements of cast blasts in ne wyoming that are triggering gsett 3 two observational results at regional distances that are replicated by these models are the excitation of 8 12s surface waves by the cast blasts and the insensitivity of peak amplitude to total explosive size for normal blasting practices the insensitivity of peak amplitudes from the cast blast to total source size is a consequence of the delay firing practice under normal procedures this practice was initiated to reduce ground motions in the near source region around the mine and it appears that it is also successful in controlling peak amplitudes at regional distances the mass transfer into the pit has both a vertical and a horizontal force component each of which contribute to the final seismogram the latter being azimuthally dependent assuming maximum coupling the contribution to the seismogram due to the vertical force component is approximately equal to the explosion contribution for pit depths of about 10 m but dominates for pit depths of 20 m or greater the contribution due to the horizontal force component is mainly in the enhanced rayleigh waves comparison of high frequency seismic radiation from the single shot and cast blast shows little qualitative difference in the regional waveforms

regional seismic discriminants using wave train energy ratios we have examined broadband regional waveforms of recent since 1988 nevada test site nts underground explosions and earthquakes throughout the southwestern united states and baja mexico recorded by terrascope and other iris stations in order to characterize seismic sources for the purposes of event identification as expected earthquakes tended to be richer in long period surface wave and short period shear wave energy relative to explosions of comparable p wave strength also explosions in general were found to be richer in 1 to 6 sec surface wave rg energy and other late arriving coda energy than were earthquakes most earthquakes show relatively little long period t 6 sec rg and surface wave coda energy which we attribute to their deeper source depths whereas known shallow earthquakes do exhibit these phases we have developed several seismic discriminants based on our observations the most promising discriminant is the ratio of short period f 1 0 hz vertical component pnl wave train energy esppz to long period 0 05 to 0 167 hz three component surface wave energy e lp 3 for this ratio explosions tend to have a higher value than do earthquakes this discriminant works on the same premise as the teleseismic mb ms ratio for which earthquakes are richer in long period surface wave energy relative to explosions with the same body wave magnitude the long period passband was chosen to limit the effect of longer period noise and to remove the effect of the coda surface waves another potential discriminant examined is the ratio of short period f 1 0 hz vertical component p wave to s wave energy esppz espsz we find that this criterion only yields marginal separation of the source populations but becomes more effective at higher frequency bands f 4 0 hz or when looking at single station observations it does however help to quantify significant short period waveform differences between the three test subsites with pahute mesa shots generating relatively little s wave energy compared to those of yucca flat for which the s wave or lg is often the largest phase while rainier s shots are intermediate in character with distinct but less prominent s waves this s wave generation is thought to be caused by near source scattering to converted phases and appears to be highly dependent on the near source geology these two discriminants are useful in that they are simple and fast to calculate using regional stations for sources 200 to 1300 km away the magnitude threshold for the esppz e lp 3 discriminant is roughly ml 4 0 the limiting factor being the signal level of the airy phase while that for the esppz espsz discriminant is roughly ml 3 0 for the same distance ranges

green ampt infiltration model for sloping surfaces 1 this work quantifies and explains the direct physical effects of slope angle on infiltration and runoff generation by extending the green ampt equation onto sloping surfaces a new extended solution using identical precipitation hydrographs was compared to the original formulation and then used to calculate the infiltration and runoff generation for different slope angles but for identical horizontal projection lengths homogeneous and isotropic soil is assumed and two different boundary conditions for vertical rainfall are studied ponded infiltration and infiltration under steady rainfall infiltration under unsteady rainfall was found to be similar to cases with steady rainfall both theoretical and numerical results show that infiltration increases with increasing slope angle for cases with ponded infiltration the slope effect was generally not significant for mild to moderate slopes but the slope effect became more important for low intensity and short duration rainfall events especially as it delayed the time for ponding it was also found that the cumulative vertical infiltration depth ihp at ponding or the initial loss increases with increasing slope angle the model was compared to richards equation on horizontal and sloping surfaces and found to perform well the model s applicability for nonuniform slopes was discussed and it was found that the model is generally applicable for isotropic and mildly anisotropic soils except for some small scale topographic elements finally the occurrence of nonvertical rainfall could increase runoff with increasing slope angle when rainfall deflects a large angle to upslope

modeling local infiltration for a two layered soil under complex rainfall patterns abstract a general model for local infiltration redistribution reinfiltration in a two layered soil profile is proposed as an extension and generalization of a formulation we developed earlier for infiltration and redistribution in crusted soils it is of analytical conceptual type and involves a runge kutta verner numerical solution of a system of two ordinary differential equations given the basic hydraulic properties of soils there are practically no parameters to estimate by calibration the wetting profile during infiltration is represented by a single similarity curve while in the reinfiltration stage which occurs for rewetting after a period of redistribution the profile of soil water content in each horizontal layer may be composed of two similarity profiles which evolve in time the model is tested by comparison with numerical solution of richards equation carried out for a variety of synthetic experiments upon the combination of three soil types of contrasting hydraulic characteristics it simulates particularly well the entire cycle infiltration redistribution reinfiltration in all cases where either layer may be less permeable the water content at the surface and the interface as well as the infiltration rates are very accurately estimated the usefulness of compound profiles of water content in the reinfiltration stage is also shown by comparison with the simple approach which relies on a single similarity curve

single force representation of earthquakes due to landslides or the collapse of caverns summary earthquakes due to landslides and the collapse of caverns are caused by the release of gravitational potential energy rather than elastic strain energy landslide or cavern collapse is assumed to start with dislocation motion along the lubricated interface of the slide block or fallen block that intersects the earth s free surface it can be shown that if each component of the dislocation vector is positionindependent and varies only as a function of time the resultant static displacement is spatially uniform both inside and outside the block and therefore no change occurs in static strain energy in particular if the medium is unbounded the static displacement is zero outside the block the force system equivalent to this dislocation model is a distribution of single forces equal but opposite to the dislocation acceleration multiplied by the density at each point of the volume constituting the slide block the physics behind the equivalence is discussed single force appears to be a common mechanism for indigeneous earthquakes that do not change the static strain field

source characterization using simplified waveforms tests on earthquakes and nuclear explosions in xinjiang china abstract complete waveforms with periods longer than 30 sec recorded at teleseismic and regional distances are used to characterize the source of several earthquakes and underground nuclear explosions in the lop nor area xinjiang china propagation effects of earth9s heterogeneities on data for several auxiliary events with well constrained source mechanisms in the vicinity of the primary event are calibrated by frequency domain division of each pair of observed and synthetic waveforms with the synthetics being computed for a reference earth model the frequency dependent deconvolution filters obtained for the auxiliary events are interpolated to construct a predicted deconvolution filter which is convolved with observed waveforms for the primary event to remove the empirically determined propagation effects and to obtain simplified waveforms that are intrinsically well predicted by the reference earth model these waveforms are then inverted for the source mechanism and centroid time location and depth of the primary event the inversion yields a centroid depth of 13 km for the 7 september 1994 earthquake m b 5 1 significantly shallower than the 33 km depth reported previously from routine determinations the centroid depth of the 5 october 1993 nuclear explosion plus tectonic release is estimated at approximately 4 km while the depth of the 21 may 1992 explosion plus tectonic release is less well resolved and may be deeper than 5 km reflecting limited resolution of the passband used here with extension to shorter period energy the method holds promise for reliable source inversion for small events in a calibrated region

the excitation of lg waves by explosions a finite difference investigation several mechanisms have been proposed to explain the excitation of the regional lg phase by explosions we examine some of these mechanisms with finite difference simulations an energy flux technique is used to analyze the synthetic signals the method is adapted from conventional array analysis techniques and gives a clear characterization of wave field intensity wave slow ness and propagation direction the vector energy flux in the model is studied instead of the scalar distribution of energy in the space time domain the cal culations show that for an explosive source in a high p wave velocity crust p wave energy cannot be effectively trapped in the crust and the nongeomet rical phase s may be the primary contributor to thelg phase for an explosive source buried in a low velocity upper crust i e where the p wave velocity is lower than the upper mantle s wave velocity part of the ps wave can be trapped in the crustal wave guide to form the lg phase the relative lg excitation de pends on the ratio between the p wave velocity in the source region and the s wave velocity in the uppermost mantle scattering effects can transfer p wave or surface wave energy into lg but the efficiency strongly depends on both the wave frequency and the characteristic size of the scatterers any source process that directly excites s waves is more efficient for generating lg than the afore mentioned mechanisms spall directly generates s wave energy and conse quently is an efficient source for lg for actual explosions all of these factors may simultaneously contribute to lg excitation determining their relative im portance and interactions requires additional observations

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

nonlinear model of tectonic release from underground explosions reversal of teleseismic rayleigh wave polarity has been observed for some underground explosions in eastern kazakh furthermore the reversed polarity rayleigh waves are observed to be time delayed by several seconds we analyze two dimensional nonlinear numerical simulations of underground explosions to examine the hypothesis that these phase reversals and apparent time delays result from the action of tectonic prestress on the explosion created nonlinear volume the shatter zone model of tectonic release we conclude that tectonic shear stress exceeding about 10 mpa 100 bars is sufficient to reverse the rayleigh wave polarity and cause an apparent time delay of several seconds even in the absence of triggered strain release on faults shear stresses of this magnitude are plausible at several hundred meters depth in that they do not exceed strength bounds for a fractured rock mass as estimated from byerlee s law the nonlinear model predictions imply that if tectonic release is modeled elastically as the relaxation of the deviatoric part of the prestress into a spherical cavity the appropriate cavity radius is approximately 80 per cent of the explosion elastic radius the apparent time delays result from interference between the explosion and tectonic source functions and can be quantitatively related to the presence of overshoot in the isotropic part of the explosion moment rate tensor it is therefore conceivable that careful observations of rayleigh wave phase for the anomalous events relative to nearby unreversed events could help constrain the amount of overshoot in the explosion source function even though the overshoot occurs on a time scale of a few tenths of a second and has a negligible effect on rayleigh wave spectral amplitudes