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

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

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

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

progressive oxidation of anoxic and ferruginous deep water during deposition of the terminal ediacaran laobao formation in south china abstract the laobao formation a black chert sequence was deposited in deep water in the terminal ediacaran nanhua basin the chert samples have finely laminated fabric and have no distinct recrystallization or metasomatic relict texture there is an extremely limited detrital component and no obvious hydrothermal influence therefore the chert appears to be an authigenic deep water precipitate the trace elements in the chert were mainly derived from seawater and thus could be a relatively unique proxy for late precambrian seawater conditions redox sensitive trace elements and relevant ratios were used to reconstruct the depositional environment of the chert sequence combined with iron species results of the laobao formation enrichments in redox sensitive trace elements u v mo depleted mn very low th u ratios 7 9 and v v ni 0 6 ratios suggest an overall anoxic and ferruginous conditions over the deposition of the chert the pyrite sulfur isotope compositions are between 15 4 and 11 0 and show a decreasing trend toward the top of the section possibly implying sulfate concentration gradually increased in the terminal ediacaran nanhua basin which is consistent with implication of their pyrite framboid diameter characteristics our data confirm that deep water in the nanhua basin was still anoxic and ferruginous and it was progressively oxidized during the terminal ediacaran period which could create necessary conditions for the emergence and rapid evolution of multicellular metazoans

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

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

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

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

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

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

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

background baseline normalization and contamination of heavy metals in the liao river watershed sediments of china abstract the quantitative assessment of heavy metal contamination in the sediments is a challenge due to the lacking of geochemical background or baseline levels and sediment heterogeneity in this study a procedure is suggested to elucidate the average background levels and geochemical baseline levels gbls of cr cu ni pb and zn in the liao river water sediments and to develop their geochemical baseline functions gbfs the average background levels of cr cu ni pb and zn were 32 6 11 1 13 1 16 3 and 37 8 mg kg respectively while their gbls the upper limit of background level were 60 21 27 23 and 96 mg kg the linear correlation of heavy metals cr cu ni pb and zn with particle size proxy elements normalizers sc fe and al was statistically significant at p

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

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

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