morphology and dynamics of explosive vents through cohesive rock formations shallow explosive volcanic processes such as kimberlite volcanism and phreatomagmatic and phreatic activity produce volcanic vents exhibiting a wide variety of morphologies including vertical pipes and v shaped vents in this study we report on experimental and numerical models designed to capture a range of vent morphologies in an eruptive system using dimensional analysis we identified key governing dimensionless parameters in particular the gravitational stress to fluid pressure ratio 2 p gh and the fluid pressure to host rock strength ratio 3 p c we used combined experimental and numerical models to test the effects of these parameters the experiments were used to test the effect of 2 on vent morphology and dynamics a phase diagram demonstrates a separation between two distinct morphologies with vertical structures occurring at high values of 2 and diagonal ones at low values of 2 the numerical simulations were used to test the effect of 3 on vent morphology and dynamics in the numerical models we see three distinct morphologies vertical pipes are produced at high values of 3 diagonal pipes at low values of 3 and horizontal sills at intermediate values of 3 our results show that vertical pipes form by plasticity dominated yielding in high energy systems high 2 and 3 whereas diagonal and horizontal vents dominantly form by fracturing in lower energy systems low 2 and 3 although our models are two dimensional they suggest that circular pipes result from plastic yielding of the host rock in a high energy regime whereas v shaped volcanic vents result from fracturing of the host rock in lower energy systems

source effects on regional seismic discriminant measurements source effects on high frequency regional seismic discriminant measurements involving p s type ratios pn lg pg lg are isolated for earthquakes in southern california and southern nevada the scatter in earthquake population discriminant measurements for fixed propagation paths is statistically analyzed to assess the spatial and frequency dependent contributions from source radiation pattern and source depth variations along with variable near source scattering this is useful because procedures for reducing the variance caused by propagation effects must be constrained by knowledge of the intrinsic scatter resulting from independent source effects for which corrections are not available without a priori knowledge of the source type and depth broadband waveforms for earthquakes near the nevada test site nts and in southern california recorded at stations of the livermore nts network lnn the caltech terrascope network and the berkeley digital seismic network bdsn are used to obtain pg lg and pn lg measurements and to assess source depth and mechanism contributions to measurement variance pn lg and pg lg spectral amplitude ratios for several frequency bands between 0 5 and 10 hz from vertical velocity waveforms are computed for a total of 18 tightly located clusters of earthquakes for each cluster we examine the correlations between observed pn lg and pg lg ratios and estimated source depths or predictions based on previously determined source mechanisms focal mechanism predictions do not match the observations well likely due to strong near source scattering and directivity effects that overwhelm the point source radiation pattern however the data do show significant scatter even for sources only a few kilometers apart source depth produces some coherent trends which can be emphasized by averaging results from multiple stations these trends vary from region to region presumably due to specific local crustal layering but most of the variance is not deterministically predictable and appears to arise from strong variations in near source scattering variance estimates for logarithmic amplitude ratios normalized by mean amplitude ratios vary from 0 01 to 0 05 for different phase pairs frequency dependent variations of the mean variance minimum and maximum amplitude ratio parameters show strong distance dependence out to about 300 km and then appear to become independent of event station distance these variance parameters appear to be suitable for use in spatial interpolations of observed p s type ratios for a specific unidentified event path as needed for nuclear test monitoring

calculations of asteroid impacts into deep and shallow water contrary to received opinion ocean impacts of small 500 m asteroids do not produce tsunamis that lead to world wide devastation in fact the most dangerous features of ocean impacts just as for land impacts are the atmospheric effects we present illustrative hydrodynamic calculations of impacts into both deep and shallow seas and draw conclusions from a parameter study in which the size of the impactor and the depth of the sea are varied independently for vertical impacts at 20 km s craters in the seafloor are produced when the water depth is less than about 5 7 times the asteroid diameter both the depth and the diameter of the transient crater scale with the asteroid diameter so the volume of water excavated scales with the asteroid volume about a third of the crater volume is vaporised because the kinetic energy per unit mass of the asteroid is much larger than the latent heat of vaporisation of water the vaporised water carries away a considerable fraction of the impact energy in an explosively expanding blast wave which is responsible for devastating local effects and may affect worldwide climate of the remaining energy a substantial portion is used in the crown splash and the rebound jet that forms as the transient crater collapses the collapse and rebound cycle leads to a propagating wave with a wavelength considerably shorter than classical tsunamis being only about twice the diameter of the transient crater propagation of this wave is hindered somewhat because its amplitude is so large that it breaks in deep water and is strongly affected by the blast wave s perturbation of the atmosphere even if propagation were perfect however the volume of water delivered per metre of shoreline is less than was delivered by the boxing day 2004 tsunami for any impactor smaller than 500 m diameter in an ocean of 5 km depth or less near field effects are dangerous for impactors of diameter 200 m or greater hurricane force winds can extend tens of kilometers from the impact point and fallout from the initial splash can be extremely violent there is some indication that near field effects are more severe if the impact occurs in shallow water

modified frequency wavenumber algorithm for regional seismograms using filon s quadrature modelling of lg waves in eastern north america summary the main focus of this study is to develop an efficient frequency wavenumber code to synthesize high frequency say 10 hz regional seismograms up to a distance of more than 1000 km in a medium consisting of a large number of crustal layers and investigate effects of regional waveguides on lg waves in this newly developed code the frequency wavenumber response is evaluated by using the filon s quadrature at high frequency and the polynomial approximation of bessei s functions implementing trapezoidal integration at low frequency this has reduced the computation time by several folds compared to the time needed for the trapezoidal integration using this algorithm both broad band seismograms at harvard and short period ectn eastern canadian telemetered network seismograms from 1988 november 25 saguenay earthquake were successfully modelled a moment magnitude of 5 9 was used initially an average waveguide was calibrated to successfully excite the regional pnl and snl waves at hrv its near surface structure constrained by matching the recorded frequency content the crust mantle transition zone was constrained by modelling the strength of the broad band snl waves consisting of sn ssmsnsmssms and ssmssms phases relative to the initial pnl waves the model was modified to consist of thin layers with an alternating high and low velocity distribution to match the high frequency ectn lg waves observed from 300 to 600 km away in addition the effect of a near surface irregular receiver structure on the duration of lg waves was also investigated by convolving its response with the regional lg seismograms initial study suggests this method as viable for modelling the entire lg waves including the coda numerical studies suggest that the shapes and peak amplitudes on lg seismograms depend more strongly on the source depth anelasticity and crustal waveguide than do the pnl seismograms

regional seismic recordings of the soviet nuclear explosion of the joint verification experiment during august and september 1988 the united states and the soviet union conducted a joint verification experiment in which each country was permitted to observe a nuclear explosion at the other country s test site using hydrodynamic means we have seismically recorded the soviet explosion at four stations at regional distances 750km and here report those observations the peak to peak particle motion in the p wave varied from 7 54 10 1 cm sec at 160 km to 1 02 10 2 cm sec at 740 km the average mb lg was 5 97 corresponding to a yield of 118 kt based on the nts mb lg yield relation of patton 1988 the average pn corner frequency of the soviet explosion was 4 hz with evidence of a second corner at about 0 7 hz both of these corners could be affected by spall near regional seismograms of the soviet jve explosion show a large arrival within the lg phase on the transverse component at all four sites this may correspond to tectonic release accompanying the explosion or to the effects of anisotropy on seismic wave propagation

comparison of seismic and hydrodynamic yield determinations for the soviet joint verification experiment of 1988 abstract seismic magnitudes determined from surface and body waves for the soviet underground nuclear explosion of september 14 1988 are used to calculate the yield of that event from previously derived calibration curves the yield obtained by combining the two seismic estimates is 113 kilotons which is very close to those obtained by hydrodynamic measurements made on site this comparison substantiates previous conclusions about the sizes of past soviet weapons tests and compliance with the threshold test ban treaty the factor of uncertainty in the combined seismic yield is 1 28 at the 68 and 1 62 at the 95 confidence levels demonstrating that accuracies considerably better than a factor of 2 can be obtained by combining seismic determinations of yield

determination of tectonic release from surface waves generated by nuclear explosions in eastern kazakhstan abstract equalized amplitudes of rayleigh waves from seven shagan river events have been compared with the radiation patterns of theoretical models in order to determine their source mechanisms the results indicate that tectonic release implies both strike slip and dip slip motion along faults striking in the northwest southeast direction consistent with the regional tectonics six events fit thrust slip models with strike azimuths fairly constricted around 144 this value agrees well with the strike azimuth of major fault systems in the source region one event fits a strike slip model striking at 123 estimated relative source strengths f factors are ranging from 0 4 to 4 0 but the estimates are sensitive to minor adjustments of the modeled fault motion

radio interferometric detection of a traveling ionospheric disturbance excited by the explosion of mount st helens a large amplitude traveling ionospheric disturbance tid was detected over owens valley california on may 18 1980 by a highly sensitive very long baseline interferometry vlbi radio astronomy experiment this tid is interpreted as the response of the ionosphere to a gravity wave excited in the neutral atmosphere by the explosion of mount st helens that took place at 1532 ut on that day a model invoking the point excitation of internal gravity waves in an isothermal atmosphere which fits observations of the tid at several other stations leads to identification of the features observed in the vlbi data small amplitude higher frequency changes in the ionosphere were detected for several hours after the passage of the large amplitude mount st helens tid but it is not clear whether these were excited by the passage of the gravity wave or were background fluctuations

nonisotropic radiation of the 2013 north korean nuclear explosion on 12 february 2013 north korea conducted an underground nuclear test in the northeastern mountainous part of the country the explosion reached magnitude mb 5 1 being recorded at most of seismic stations around the world and becoming one of the best ever recorded nuclear explosions in history similarly as other nuclear explosions buried in nevada kazakhstan or china the 2013 north korean explosion is characterized by a significant nonisotropic radiation this radiation is manifested by distinct sh and love waves in the wave field and is inconsistent with the model of a spherically symmetric source we show that the love waves are not generated by a tectonic earthquake triggered on a nearby fault structures but produced by asymmetry of the explosive source caused by presence of deviatoric stress in the surrounding rock the retrieved moment tensor of the 2013 explosion is characterized by the isotropic component of 57 5 the double couple component of 17 9 and the compensated linear vector dipole component of 24 7 the p t and n axes of the moment tensor are consistent with the principal axes of the regional tectonic stress in the korean peninsula a comparison of waveforms and particle motions of the 2013 explosion and the previous north korean nuclear explosion buried in 2009 indicates that the 2013 explosion was slightly more nonisotropic

experimental craters formed by single and multiple buried explosions and implications for volcanic craters with emphasis on maars 1 craters at many volcanoes including most maars are formed by multiple subsurface explosions experiments compared the crater formed by a single large buried explosion with craters formed by multiple explosions with the same cumulative energy explosive charges were detonated in pads composed of layered aggregates in three configurations 1 a single large charge buried near its optimal crater excavation depth 2 three charges each with 1 3 the energy of the first one buried at approximately the same depth with respect to the original pad surface 3 the same three charges buried successively deeper final crater size in the multiple explosion cases is not a good indicator of the energy of individual explosions however crater morphology and ejecta volume and distribution can be good indicators of explosion energy and depth these results directly impact the estimate of the energy released by past maar eruptions and future hazard assessments

waveform modeling of the november 1987 superstition hills earthquakes long period body wave data recorded at teleseismic distances and strong motion data at pasadena for the superstition hills earthquakes of 24 november 1987 are modeled to obtain the source parameters we will refer to the event that occurred at 0153 ut as eq1 and the event at 1316 ut as eq2 at all distances the first earthquake appears to be a simple left lateral strike slip event on a fault striking ne it is a relatively deep event with a source depth of 10 km it has a teleseismic moment of 2 7 10 25 dyne cm the second and more complex event was modeled in two ways by using eq1 as the green s function and by using a more traditional forward modeling technique to create synthetic seismograms the first method indicated that eq2 was a double event with both subevents similar but not identical to eq1 and separated by about 7 5 sec from the synthetic seismogram study we obtained a strike of 305 for the first subevent and 320 for the second both have dips of 80 and rakes of 175 the first subevent has a moment of 3 6 10 25 which is half that of the second we obtain depths of at least 6 km the teleseismic data indicate a preferred subevent separation of 30 km with the second almost due south of the first but the error bounds are substantial this would suggest that the subevents occurred on conjugate faults the strong motion data at pas however imply a much smaller source separation with the sources probably produced by asperities

complex faulting deduced from broadband modeling of the 28 february 1990 upland earthquake ml 5 2 the 1990 upland earthquake was one of the first sizable local events to be recorded broadband at pasadena where the green s functions appropriate for the path are known from a previous study the synthetics developed in modeling the 1988 upland sequence were available for use in rapid assessment of the activity first motion studies from the caltech usgs array data gave two solutions for the 1990 main shock based on the choice of regional velocity models although these focal mechanisms differ by less than 5 in strike and 20 rake it proved possible to further constrain the solution using these derived green s functions and a three component waveform inversion scheme we obtain from long period waves a fault plane solution of 216 77 5 0 m 0 2 5 10 24 dyne cm depth 6 km and a source duration of 1 2 sec for which the orientation and source depth are in good agreement with the first motion results of hauksson and jones 1991 comparisons of the broadband displacement records with the high pass wood anderson simulations suggests the 1990 earthquake was a complicated event with a strong asperity at depth double point source models indicate that about 30 per cent of the moment was released from a 9 km deep asperity following the initial source by 0 0 to 0 5 sec our best fitting distributed fault model indicates that the timing of our point source results is feasible assuming a reasonable rupture velocity the rupture initiated at a depth of about 6 km and propagated downward on a 3 5 by 3 5 km length by width fault both the inversion of long period waves and the distributed fault modeling indicate that the main shock did not rupture the entire depth extent of the fault defined by the aftershock zone a relatively small asperity about 1 0 km 2 with a greater than 1 kbar stress drop controls the short period wood anderson waveforms this asperity appears to be located in a region where seismicity shows a bend in the fault plane

inversion of surface wave spectra for source parameters of large earthquakes using aspherical earth models abstract amplitude and phase spectra of rayleigh and love waves of periods of 150 to 300 s from eight large earthquakes which occurred between 1990 and 1993 are corrected for wave propagation and then inverted for the source duration rupture directivity and moment tensor of the earthquake source for various propagation anomalies predicted by models of the earth s aspherical elastic and anelastic structure the application of corrections for the focusing and take off azimuth anomaly in addition to conventional corrections for the phase anomaly improves inversions of surface waves rayleigh waves provide better constraints than love waves in the determination of source parameters the data consist of either only rayleigh waves or both love and rayleigh waves whenever the full moment tensor is involved for several earthquakes there is clear discrepancy between source parameters determined from different data sets particularly from rayleigh or love waves the moment tensor solution tends to underpredict observed amplitude spectra for data sets with large amplitude anomalies especially for love waves this study shows that 1 the 1990 sudan earthquake is anomalous for its unusually large non double couple component of the moment tensor 2 the 1990 iran earthquake has a strike slip mechanism with a subvertical nw striking nodal plane which is the fault plane inferred from surface ruptures 3 the 1991 costa rica earthquake may have a seismic moment larger than previously determined from long period surface waves 4 the 1992 nicaragua earthquake involves a predominant rupture parallel to the trench and a large centroid offset up dip to the trench axis and the latter process may be responsible for large tsunami generation 5 the 1993 hokkaido earthquake has a shallow dipping and west plunging nodal plane which is consistent with the p wave first motions but differs from the centroid moment tensor solutions

an integrated study of crustal structure and regional wave propagation for southeastern missouri teleseismic receiver function analysis and published refraction studies are used to infer the existence of first order discontinuities within the crust and mantle of the ozark uplift at the incorporated research institutions in seismology iris station cathedral cave missouri ccm this information is then used to study the nature of regional wave propagation from the new madrid seismic zone to ccm across the ozark dome to interpret broadband seismograms written by small events receiver function inversion indicates a crust 40 km thick characterized by smooth velocity gradients down to the moho secondary ps conversions late in the receiver functions show the existence of a high velocity mantle layer 10 to 15 km thick at approximately 60 km depth with p wave velocity of about 8 5 km sec the data resolve both the top and bottom of the layer such high velocities suggest rocks with eclogite or dunite compositions regional data from the 26 september 1990 cape girardeau earthquake m 1 4 7 are used to model average crustal velocities and the nature of the velocity gradient near the moho through inversion of relative arrival times of observed phases regional p and s waveforms are exceptionally simple at ranges of 180 km showing the mantle head waves pn and sn with a triplicated pg and sg arriving within a few seconds respectively sp is quite prominent and is an accurate indicator of source depth for the cape girardeau event which occurred between 14 and 16 km depth there is no evidence for other major phases except rg after the sg arrival confirming the observation that the crust is dominated by smooth velocity gradients a grid search technique is used to model relative phase amplitudes to obtain the focal mechanism for the cape girardeau event allowable focal mechanisms are dominated by thrust faults striking ns or ne sw the inferred earth structure is used to model the 4 may 1991 risco event m 1 4 6 but observed differences in relative arrival times between p s and rayleigh phases suggest that crustal velocities are slightly lower within the mississippi embayment and that the uppermost mantle has a higher positive gradient than further northwest nevertheless sp constrains the source depth between 7 and 9 km and p sv and sh wave amplitudes yield mechanisms consistent with that obtained by the portable array for numerical data acquisition panda deployment waveforms from two small events with poor signal to noise ratios are compared with waveforms of the larger events to infer source depths modeling broadband waveforms from small local and regional events shows great promise in determining source parameters and inferring details of crustal and upper mantle structure however lateral heterogeneity in velocity structure will remain one of the principal obstacles to overcome

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

phase analysis of rayleigh waves from the shagan river test site in the ussr abstract a study was made to determine if significant phase differences exist between rayleigh waves which have traveled almost identical paths from the ussr shagan river test site surface waves from five explosions recorded at six sro asro digital stations were used in the analysis the explosion of 4 august 1979 was selected as a reference and at each site the phase spectra of the rayleigh waves from the other five events were compared to that of the reference the technique of phase matched filtering was used to analyze the signals this technique reduces the effects of multipathing and removes phase differences due to dispersion along slightly different travel paths each epicenter had been relocated by using calibration data from the cratering shot of 15 january 1965 and remaining errors in location and origin time are considered to be extremely small seismograms were analyzed for surface waves recorded at matsushiro japan majo shillong india shio kabul afghanistan kaao ankara turkey anto grafenburg west germany grfo and albuquerque new mexico anmo results of the study indicate that rayleigh waves from some shagan river explosions have undergone large phase shifts relative to rayleigh waves which have traveled almost identical paths from other shagan river explosions in some cases the phase shifts can be interpreted as complete phase reversals with associated time delay in particular as compared to the explosion of 4 august 1979 rayleigh waves from the explosion of 7 july 1979 are reversed in polarity at kaao and anto and are reversed in polarity and delayed at grfo shio and majo

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

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

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

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

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

broadband modelling of regional seismograms imperial valley to pasadena summary this paper addresses broadband wave propagation along a corridor from imperial valley to pasadena california the path consists of 50 km of slow basin structure with a shallow moho followed by 250 km of relatively normal southern california structure approaching pasadena events occurring in the valley produce extended body wave codas which carry a dispersive waveform imprint along with longer period rayleigh waves many features of these seismograms at periods greater than a few seconds can be modelled by applying a finite difference technique to a 2 d structure shorter periods display complex behaviours not easily modelled by present techniques especially for shallow events events occurring in the normal structure produce broadband sh waveforms that can be modelled analytically if some extra empirically derived alignment parameters determined from calibration events are used these parameters are determined by adjusting traveltime differentials between the decomposed wavefield s ss etc for example delays in ss relative to s correspond to local corrections for sediment cover for a particular source region source complexity such as asperities and directivity become increasingly important at shorter periods as demonstrated by numerical experiments and observation

the determination of source parameters for small earthquakes from a single very broadband seismic station the installation of very broadband seismic stations makes it possible to recover the source parameters of small earthquakes 2 5 ml 5 0 which occur at local and regional distances if the gross crustal structure along the travel path is known it is possible to use the p sv and sh displacement waveforms from a single station to determine the seismic moment tensor although the details of the crustal structure strongly affect the body waveforms at regional distances the signature of the seismic source orientation on the waveform is robust at frequencies less than 1 3 hz we explore the trade offs between crustal model hypocentral depth and filtering for a linear moment tensor inversion procedure the procedure is tested on two small earthquakes which occurred in the rio grande rift and were recorded at the iris usgs station anmo the agreement between the single station moment tensor inversion fault plane parameters and those determined from local first motions is excellent

dynamics of dikes versus cone sheets in volcanic systems igneous sheet intrusions of various shapes such as dikes and cone sheets coexist as parts of complex volcanic plumbing systems likely fed by common sources how they form is fundamental regarding volcanic hazards yet no dynamic model simulates and predicts satisfactorily their diversity here we present scaled laboratory experiments that reproduced dikes and cone sheets under controlled conditions our models show that their formation is governed by a dimensionless ratio 1 which describes the geometry of the magma source and a dynamic dimensionless ratio 2 which compares the viscous stresses in the flowing magma to the host rock strength plotting our experiments against these two numbers results in a phase diagram evidencing a dike and a cone sheet field separated by a sharp transition that fits a power law this result shows that dikes and cone sheets correspond to distinct physical regimes of magma emplacement in the crust for a given host rock strength cone sheets preferentially form when the source is shallow relative to its lateral extent orwhen the magma influx velocity or viscosity is high conversely dikes form when the source is deep compared to its size or when magma influx rate or viscosity is low both dikes and cone sheets may form fromthe same source the shift fromone regime to the other being then controlled by magma dynamics i e different values of 2 the extrapolated empirical dike to cone sheet transition is in good agreement with the occurrence of dikes and cone sheets in various natural volcanic settings

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

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

evidence of tectonic release from underground nuclear explosions in long period s waves the sh waves from 21 underground nuclear explosions at pahute mesa nts were used to investigate tectonic release the equivalent double couple representation of the tectonic release which was constrained by waveform modeling and the polarity of sp is very similar for all the explosions the average orientation is a right lateral strike slip fault trending n15 w seismic moments were determined on the basis of comparisons with two western united states strike slip earthquakes benham has the largest tectonic release moment 5 6 10 24 dyne cm and stilton 0 1 10 24 dyne cm the smallest of the events studied in general the seismic moments increase with the size of the explosion but the location of the explosion relative to previous explosions can strongly affect the tectonic release the pahute mesa events can be separated into two populations 1 events which are well separated 4 km from previous explosions and 2 those events which are close 4 km to previous explosions those events which are close to previous explosions show a marked decrease in tectonic release a least squares fit of seismic moment to event size as determined from the world wide average ab amplitude shows that the two populations are approximately parallel but offset the fact that the trends remain separated even at small yields e g pipkin and scotch suggests that for pahute mesa there is not a threshold for tectonic release since spatial position gives the best separation of high and low tectonic release events a volume model is favored for the source mechanism the preferred model is motion on a system of faults and joints

surface wave group velocity tomography of east asia abstract group velocities of both rayleigh and love waves are used in a tomographic inversion to obtain group velocity maps of east asia 60 140 e and 20 60 n the period range studied is 30 70 s the tibetan plateau a region undergoing intense north south compression appears as a prominent low velocity about 15 from the average structure in this area central tibet appears as the area with the lowest velocities and southern tibet south of the zangbo suture zone and the himalayas is an area of high velocities the tibet low velocity area extends northward to the southern tarim basin the north china korean platform an area traditionally recognized as the oldest platform in china does not have a consistent crust and upper mantle velocity signature the north china plain a part of the platform where extensional tectonics dominates is an area of high velocities probably as a result of thin crust the other parts of the platform have relatively low velocities the south china block the least tectonically active region of china is generally an area of high velocity for periods longer than 40 s a high group velocity gradient clearly exists along longitude 105 e the velocities are noticeably higher east of this longitude than west of it this transition corresponds closely to that in the bouguer gravity map in general processes in the crust and upper mantle owing to recent tectonic activities rather than the age of the basement rocks seem to have dominant control of crust and upper mantle velocity structures

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

geology of the chinese nuclear test site near lop nor xinjiang uygur autonomous region china abstract the chinese underground nuclear test site in the kuruktag and kyzyltag mountains of the xinjiang uygur autonomous region of northwest china is the location of sixteen underground tests that occurred between 1969 and 1992 the largest test to date conducted on 21 may 1992 had a reported yield of about one megaton geophysical properties of the rocks and a large scale geologic map of part of the test area were published by the chinese in 1986 and 1987 and are the first site specific data available for this test site in areas of low relief underground nuclear testing has occurred below the water table in shafts drilled vertically into dense low porosity paleozoic granitic and metasedimentary rocks additional testing in areas of more rugged terrain has occurred in horizontal tunnels probably abovethe water table at least one of these tunnels was driven into granite the upper 50 m of the rock in the area of the vertical tests is weathered and fractured these conditions have been shown to influence the magnitude of the disturbance of the land surface after a nuclear explosion these descriptions suggest hard rock coupling at depth and a closer resemblance to the former soviet test site in eastern kazakhstan than to the u s test site in nevada

evidence of tectonic release in long period s waves from underground nuclear explosions at the novaya zemlya test sites abstract evidence of tectonic release produced by underground nuclear explosions at novaya zemlya is present in teleseismic long period s waves sh waveforms from representative events at the southern and northern novaya zemlya test sites were modeled to determine the sh radiation patterns long period p and sv waves were also investigated to further constrain the equivalent double couple orientation of the tectonic release events within each test site have similar faulting mechanisms but there are definite differences in the tectonic release orientation between the two sites the southern test site double couple orientation is either vertical strike slip or 45 dipping thrust while the northern test site has an oblique normal dip slip orientation the limited resolution of sh signals and complexity of the observed sv waveforms along with uncertainties in the absolute explosion source strengths and t prevent unique solutions for both test sites assuming a strike slip orientation the 27 october 1973 southern novaya zemlya event has the largest tectonic release moment 1 6 10 24 dyne cm and 14 october 1969 northern event has the smallest moment 0 9 10 23 dyne cm of the 12 events studied the ratio of tectonic release moment to explosion strength varies by as much as a factor of 3 at the northern test site and by a factor of 2 at the southern site the variability of the tectonic release orientation and strength at the two test sites allows us to address the question of whether tectonic release affects yield estimation