Explosion Monitoring Research Articles

Simulation of topographic effects on seismic waves from shallow explosions near the North Korean nuclear test site with emphasis on shear wave generation

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.

Ten Years of Development of Equipment for Measurement of Atmospheric Radioactive Xenon for the Verification of the CTBT

Atmospheric measurement of radioactive xenon isotopes (radioxenon) plays a key role in remote monitoring of nuclear explosions, since it has a high capability to capture radioactive debris for a wide range of explosion scenarios. It is therefore a powerful tool in providing evidence for nuclear testing, and is one of the key components of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The reliability of this method is largely based on a well-developed measurement technology. In the 1990s, with the prospect of the build-up of a monitoring network for the CTBT, new development of radioxenon equipment started. This article summarizes the physical and technical principles upon which the radioxenon technology is based and the advances the technology has undergone during the last 10 years. In contrast to previously used equipment, which was manually operated, the new generation of radioxenon monitoring equipment is designed for automated and continuous operation in remote field locations. Also the analytical capabilities of the equipment were strongly enhanced. Minimum detectable concentrations of the recently developed systems are well below 1 mBq/m3 for the key nuclide 133Xe for sampling periods between 8 and 24 h. All the systems described here are also able to separately measure with low detection limits the radioxenon isotopes 131mXe, 133mXe and 135Xe, which are also relevant for the detection of nuclear tests. The equipment has been extensively tested during recent years by operation in a laboratory environment and in field locations, by performing comparison measurements with laboratory type equipment and by parallel operation. These tests demonstrate that the equipment has reached a sufficiently high technical standard for deployment in the global CTBT verification regime.

High-precision Location of North Korea's 2009 Nuclear Test

On 25 May 2009, the Democratic People's Republic of Korea (North Korea) announced that it had conducted a second nuclear test, without providing information of exact time, location, and yield. On that day, the United States Geological Survey (USGS) reported detecting a magnitude 4.7 seismic tremor in an aseismic region in North Korea (http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009hbaf.php; also archived copy at http://geophysics.geo.sunysb.edu/wen/NK/usgs\_north\_korea\_2009\_test.webarchive). The seismic waveform features recorded at the seismic stations around the globe for the event exhibit characteristics of an explosion. However, the exact location of the test remains elusive. Seismic monitoring of underground nuclear explosions relies on seismic observations recorded by seismometers around the globe. Because seismic observations are influenced by the seismic properties along the paths of the wave propagation from the source to the seismometers, the accuracy of determination of an event location and time depends on the degree of our knowledge of the seismic properties in the interior of the Earth. The challenge in accurately determining the location of North Korea's nuclear tests stems from the fact that, due to the lack of seismic stations and seismicity in the region, the seismic structure is not known in enough detail that its influence can be well calibrated. For example, the horizontal uncertainty of the 2009 event location reported by the USGS is about ±3.8 km (http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2009hbaf.php). While our knowledge of the seismic structure in the region is unlikely to improve soon, in this study we demonstrate a strategy that uses the forensic evidence registered by North Korea's 2006 nuclear test to determine the location of the 2009 test in high precision, and we present our determination of the location of the 2009 test. ### Scientific Evidence Registered by the 2006 Test The possible location of North Korea's 2006 test is identified by satellite images (http://cryptome.org/eyeball/dprk-test/dprktest.htm; also an archived copy at http://geophysics.geo.sunysb.edu/wen/NK/eyeball.webarchive) (Table 1). High-quality …

Considerations in Phase Estimation and Event Location Using Small-aperture Regional Seismic Arrays

The global monitoring of earthquakes and explosions at decreasing magnitudes necessitates the fully automatic detection, location and classification of an ever increasing number of seismic events. Many seismic stations of the International Monitoring System are small-aperture arrays designed to optimize the detection and measurement of regional phases. Collaboration with operators of mines within regional distances of the ARCES array, together with waveform correlation techniques, has provided an unparalleled opportunity to assess the ability of a small-aperture array to provide robust and accurate direction and slowness estimates for phase arrivals resulting from well-constrained events at sites of repeating seismicity. A significant reason for the inaccuracy of current fully-automatic event location estimates is the use of f−k slowness estimates measured in variable frequency bands. The variability of slowness and azimuth measurements for a given phase from a given source region is reduced by the application of almost any constant frequency band. However, the frequency band resulting in the most stable estimates varies greatly from site to site. Situations are observed in which regional P- arrivals from two sites, far closer than the theoretical resolution of the array, result in highly distinct populations in slowness space. This means that the f−k estimates, even at relatively low frequencies, can be sensitive to source and path-specific characteristics of the wavefield and should be treated with caution when inferring a geographical backazimuth under the assumption of a planar wavefront arriving along the great-circle path. Moreover, different frequency bands are associated with different biases meaning that slowness and azimuth station corrections (commonly denoted SASCs) cannot be calibrated, and should not be used, without reference to the frequency band employed. We demonstrate an example where fully-automatic locations based on a source-region specific fixed-parameter template are more stable than the corresponding analyst reviewed estimates. The reason is that the analyst selects a frequency band and analysis window which appears optimal for each event. In this case, the frequency band which produces the most consistent direction estimates has neither the best SNR or the greatest beam-gain, and is therefore unlikely to be chosen by an analyst without calibration data.

Design of aerosol sampler to remove radon and thoron progeny interference from aerosol samples for nuclear explosion monitoring

A Nuclear Explosion Monitoring Inertial Impactor (NEMII) system was developed to physically separate naturally occurring radionuclides from those produced in nuclear weapons explosions. Studies show that aerosols containing natural activity have an aerodynamic diameter in the range of 0.1–1.0 μm. It has been established that atmospheric nuclear explosions produce radioactive aerosols with aerodynamic diameters 1.0 μm and 1.0 μm, between 0.1 and 1.0 μm, and smaller than 0.1 μm. Calculations based on previous work for high-volume impactors were completed to obtain the impactor geometry that yields the desired cutoff values. The components of the aerosol impactor were manufactured or obtained and then assembled. In addition, a submicrometer aerosol generation system was assembled to benchmark the NEMII system against a commercial Micro-Orifice Uniform-Deposit Impactor (MOUDI). The MOUDI was also used to verify the naturally occurring radioactivity distribution using 212Pb gamma spectra.

Using Ancillary Information to Improve Hypocenter Estimation: Bayesian Single Event Location (BSEL)

We have developed and tested an algorithm, Bayesian Single Event Location (BSEL), for estimating the location of a seismic event. The main driver for our research is the inadequate representation of ancillary information in the hypocenter estimation procedure. The added benefit is that we have also addressed instability issues often encountered with historical NLR solvers (e.g., non-convergence or seismically infeasible results). BSEL differs from established nonlinear regression techniques by using a Bayesian prior probability density function (prior PDF) to incorporate ancillary physical basis constraints about event location. P-wave arrival times from seismic events are used in the development. Depth, a focus of this paper, may be modeled with a prior PDF (potentially skewed) that captures physical basis bounds from surface wave observations. This PDF is constructed from a Rayleigh wave depth excitation eigenfunction that is based on the observed minimum period from a spectrogram analysis and estimated near-source elastic parameters. For example, if the surface wave is an Rg phase, it potentially provides a strong constraint for depth, which has important implications for remote monitoring of nuclear explosions. The proposed Bayesian algorithm is illustrated with events that demonstrate its congruity with established hypocenter estimation methods and its application potential. The BSEL method is applied to three events: 1) A shallow Mw 4 earthquake that occurred near Bardwell, KY on June 6, 2003, 2) the Mw 5.6 earthquake of July 26, 2005 that occurred near Dillon, MT, and 3) a deep Mw 5.7 earthquake that occurred off the coast of Japan on April 22, 1980. A strong Rg was observed from the Bardwell, KY earthquake that places very strong constraints on depth and origin time. No Rg was observed for the Dillon, MT earthquake, but we used the minimum observed period of a Rayleigh wave (7 seconds) to reduce the depth and origin time uncertainty. Because the Japan event was deep, there is no observed surface wave energy. We utilize the prior generated from the Dillon, MT event to show that even in the case when a prior is inappropriately applied, high quality data will overcome its influence and result in a reasonable hypocenter estimate.

Broad-bandLgattenuation modelling in the Middle East

We present a broad-band tomographic model of Lg attenuation in the Middle East derived from source- and site-corrected amplitudes. Absolute amplitude measurements are made on hand-selected and carefully windowed seismograms for tens of stations and thousands of crustal earthquakes resulting in excellent coverage of the region. A conjugate gradient method is used to tomographically invert the amplitude data set of over 8000 paths over a 45°× 40° region of the Middle East. We solve for Q variation, as well as site and source terms, for a wide range of frequencies ranging from 0.5 to 10 Hz. We have modified the standard attenuation tomography technique to more explicitly define the earthquake source expression in terms of the seismic moment. This facilitates the use of the model to predict the expected amplitudes of new events, an important consideration for earthquake hazard or explosion monitoring applications. The attenuation results have a strong correlation to tectonics. Shields have low attenuation, whereas tectonic regions have high attenuation, with the highest attenuation at 1 Hz found in eastern Turkey. The results also compare favourably to other studies in the region made using Lg propagation efficiency, Lg/Pg amplitude ratios and two-station methods. We tomographically invert the amplitude measurements for each frequency independently. In doing so, it appears the frequency dependence of attenuation in all regions is not compatible with the power-law representation of Q( f ), an assumption that is often made.

The Prospect of Using Three-Dimensional Earth Models to Improve Nuclear Explosion Monitoring and Ground-motion Hazard Assessment

Research Article| January 01, 2009 The Prospect of Using Three-Dimensional Earth Models to Improve Nuclear Explosion Monitoring and Ground-motion Hazard Assessment John J. Zucca; John J. Zucca 1Lawrence Livermore National Laboratory Search for other works by this author on: GSW Google Scholar William R. Walter; William R. Walter 1Lawrence Livermore National Laboratory Search for other works by this author on: GSW Google Scholar Arthur J. Rodgers; Arthur J. Rodgers 1Lawrence Livermore National Laboratory Search for other works by this author on: GSW Google Scholar Paul Richards; Paul Richards 2Lamont-Doherty Earth Observatory Search for other works by this author on: GSW Google Scholar Michael E. Pasyanos; Michael E. Pasyanos 1Lawrence Livermore National Laboratory Search for other works by this author on: GSW Google Scholar Stephen C. Myers; Stephen C. Myers 1Lawrence Livermore National Laboratory Search for other works by this author on: GSW Google Scholar Thorne Lay; Thorne Lay 3University of California Santa Cruz Search for other works by this author on: GSW Google Scholar Dave Harris; Dave Harris 1Lawrence Livermore National Laboratory Search for other works by this author on: GSW Google Scholar Tarabay Antoun Tarabay Antoun 1Lawrence Livermore National Laboratory Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2009) 80 (1): 31–39. https://doi.org/10.1785/gssrl.80.1.31 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John J. Zucca, William R. Walter, Arthur J. Rodgers, Paul Richards, Michael E. Pasyanos, Stephen C. Myers, Thorne Lay, Dave Harris, Tarabay Antoun; The Prospect of Using Three-Dimensional Earth Models to Improve Nuclear Explosion Monitoring and Ground-motion Hazard Assessment. Seismological Research Letters 2009;; 80 (1): 31–39. doi: https://doi.org/10.1785/gssrl.80.1.31 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search The past 10 years have brought rapid growth in the development and use of three-dimensional (3D) seismic models of Earth structure at crustal, regional, and global scales. In order to explore the potential for 3D seismic models to contribute to important societal applications, Lawrence Livermore National Laboratory (LLNL) hosted a Workshop on Multi-Resolution 3D Earth Models to Predict Key Observables in Seismic Monitoring and Related Fields on 6–7 June 2007, in Berkeley, California. The workshop brought together academic, government, and industry leaders in research programs developing 3D seismic models and methods for nuclear explosion monitoring and seismic ground-motion hazard assessment.... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Fission product ratios as treaty monitoring discriminants

The International Monitoring System (IMS) of the Comprehensive Test Ban Treaty Organization (CTBTO) is currently under construction. The IMS is intended for monitoring of nuclear explosions. The radionuclide part of the IMS monitors the atmosphere for short-lived radioisotopes indicative of a nuclear weapon test, and includes field collection and measurement stations, as well as laboratories to provide reanalysis of the most important samples and a quality control function. The Pacific Northwest National Laboratory in Richland, Washington hosts the United States IMS laboratory, with the designation “RL16.” Since acute reactor containment failures and chronic reactor leakage may also produce similar isotopes, it is tempting to compute ratios of detected isotopes to determine the relevance of an event to the treaty or agreement in question. In this paper we will note several shortcomings of simple isotopic ratios: (1) fractionation of different chemical species, (2) difficulty in comparing isotopes within a single element, and (3) the effect of unknown decay times. While these shortcomings will be shown in the light of an aerosol sample, several of the problems extend to xenon isotopic ratios. Due to the difficulties listed above, considerable human expertise will be required to convert a simple mathematical isotope ratio into a criterion which will reliably categorize an event as ‘reactor’ or ‘weapon’.

Hydroacoustic blockage prediction and measurement at Diego Garcia using the Adiabatic Mode Parabolic Equation Model

Underwater explosion monitoring with sparse sensors at long ranges relies on the efficient propagation of acoustic energy in the sound fixing and ranging (SOFAR) channel. When sound traveling in this channel encounters an island or seamount, it will either diffract, scatter, or be converted into seismic energy. Signals observed on the opposite side of these obstructions have been affected by some combination of these processes, and models of global detection and localization depend on knowing these effects. We present a study using the Adiabatic Mode Parabolic Equation (AMPE) model to predict these processes in three dimensions at the Chagos Archipelago. Predictions at 5, 10, and 20 Hz are compared with measurements of approximately 300 T-wave signals from six years of earthquakes on either side of the Chagos Archipelago. These have been recorded at the hydrophone arrays around Diego Garcia. The result of this 360-degree analysis, and the agreement with observed data, demonstrate the utility of the model in understanding the physical effects of these obstructions.

A comparison of infrasound signals refracted from stratospheric and thermospheric altitudes

Over the last several years, a large number of ground‐based infrasound arrays have been established for explosion monitoring as part of the International Monitoring System of the Comprehensive Nuclear Test Ban Treaty Organization. Results from these arrays have become valuable in understanding long‐range infrasound propagation in the atmosphere and complement earlier data. Two types of signals are often observed for a given source: those refracted at stratospheric heights and at thermospheric heights. In this contribution we compare several characteristics of these two signal types including observed pressure amplitude, average travel velocity, bearing, and signal duration. For this study we use archival data from atmospheric nuclear explosions, high explosive chemical explosions on the surface, earthquakes with previously detected stratospheric signals, and earthquakes for which stratospheric signals were not detected. We show that the combination of stratospheric and thermospheric signals may provide independent estimates of wind propagation conditions and source characteristics. The observations of both signal types may increase the confidence level of an infrasound signal detection.

Overview of Open Seismic Data from the North Korean Event of 9 October 2006

Research Article| March 01, 2008 Overview of Open Seismic Data from the North Korean Event of 9 October 2006 Keith D. Koper; Keith D. Koper Department of Earth and Atmospheric Sciences Saint Louis University 3642 Lindell Blvd. St. Louis, Missouri 63108 USA kkoper@gmail.com (K. D. K.) Search for other works by this author on: GSW Google Scholar Robert B. Herrmann; Robert B. Herrmann Department of Earth and Atmospheric Sciences Saint Louis University 3642 Lindell Blvd. St. Louis, Missouri 63108 USA kkoper@gmail.com (K. D. K.) Search for other works by this author on: GSW Google Scholar Harley M. Benz Harley M. Benz Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2008) 79 (2): 178–185. https://doi.org/10.1785/gssrl.79.2.178 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Keith D. Koper, Robert B. Herrmann, Harley M. Benz; Overview of Open Seismic Data from the North Korean Event of 9 October 2006. Seismological Research Letters 2008;; 79 (2): 178–185. doi: https://doi.org/10.1785/gssrl.79.2.178 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search On 9 October 2006 North Korea announced that it had conducted a nuclear weapons test, its first, at the Chik-tong test site in north Hamgyeong Province. It had been more than eight years since the world's last known nuclear test, carried out by Pakistan on 30 May 1998 (Wallace 1998). The North Korean event was small (4.2 mb) and occurred in a part of the world with a relatively low density of accessible (open) broadband seismometers. Therefore, it provides a nice test of the nuclear explosion monitoring capability of the open global seismic network, which is... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Detection and characterization of seismic phases using continuous spectral estimation on incoherent and partially coherent arrays

Seismic arrays are employed in the global monitoring of earthquakes and explosions because of their superior ability to detect and estimate the direction of incident seismic arrivals. Traditional beamforming and f–k analysis require waveform semblance over the full array aperture and cannot be applied in many situations where signals are incoherent between sensors. The NORSAR and MJAR arrays are two primary IMS stations where this is the case for high-frequency regional phases. Large intersite distances and significant geological heterogeneity at these arrays result in waveform dissimilarity which precludes coherent array processing in the frequency bands with optimal SNR. Multitaper methods provide low variance spectral estimates over short time-windows and seismic arrivals can be detected on single channels using a non-linear spectrogram transformation which attains local maxima at times and frequencies characterized by an energy increase. This detection procedure requires very little a priori knowledge of the spectral content of the signal. The transformed spectrograms can be beamformed over large-aperture arrays or networks according to theoretical time-delays resulting in an incoherent detection system which does not require waveform semblance at any frequencies. We outline a real-time automatic detection system for regional phase arrivals on the NORSAR array and demonstrate how stable and accurate slowness and azimuth estimates can be obtained for quite marginal signals. In the case of partially coherent arrays, the procedure described may provide stable, if low resolution, estimates which can subsequently be refined using coherent processing over subsets of sensors. In particular, we illustrate how the spectrogram beamforming method facilitates a stable and accurate slowness estimate for the incoherent high-frequency Pn arrival at the MJAR array in Japan from the 2006 October 9 underground nuclear test in North Korea.

Source Spectral Modeling of Regional P/S Discriminants at Nuclear Test Sites in China and the Former Soviet Union

Theoretical understanding of regional P/S discriminants has been a long- standing research topic with important implications for nuclear explosion monitoring. The observation that discrimination is poor at low frequencies, but becomes significant at higher frequencies, usually at about 3 to 4 Hz, particularly needs understanding. To gain insight, source and attenuation models are used to predict spectra of regional seismic phases ( Pn, Sn , and Lg ) for nuclear explosions and selected earthquakes near the Lop Nor, Semipalatinsk (Balapan and Degelen Mountain), and Novaya Zemlya test sites in China and the former Soviet Union. A modified Brune (1970) model (a la Walter and Taylor, 2002) is used to predict P - and S -source terms for earthquakes. A Mueller/Murphy (1971) model is used for explosions, including a new conjecture that the S waves may be modeled by the same functional form as for P waves, but with corner frequency reduced by the ratio of near-source shear and compressional velocities, vs ( S )/ vs ( P ). Results indicate that the frequency dependence of Pn / Sn and Pn / Lg discrimination performance at all of these hard-rock test sites is primarily due to differences in the corner frequencies of P and S waves for explosions, qualitatively consistent with observations by Xie and Patton (1999) for Lop Nor. P / S discrimination emerges at the explosion S -wave corner frequency and does not improve above the P -wave corner frequency. Scaling of the explosion S -wave corner frequency with elastic radius as vs ( S )/ Re at all of these test sites suggests that major contributions to S -wave generation from explosions may be occurring at the same distance scale (i.e., the elastic radius) as P waves from explosions. The explicit physical mechanism of this near-source S -wave generation is still being investigated. Implications regarding application of regional P / S discriminants are discussed.

LOOKING BACKWARD, FACING FORWARD

Our year of commemorating the centennial of the Seismological Society of America is drawing to a close. We have had an opportunity to reflect on our long and proud history and to take a fresh look at preserving materials from our early years. During this process someone pointed out to me that I have been the chief staffer at SSA for more than one-third of the Society's existence. Once I recovered from the personal implications of that observation, I began to review the many changes I've seen in my years with SSA. When I arrived in 1970, membership in scientific societies was viewed as a civic duty, a special responsibility to support the advancement of one's field of knowledge. From the early minutes, we can see that the SSA founders had big ambitions for the Society. However, by the time I arrived in January 1970, the identity of SSA was defined as much by what it did not do as by what it did. At some point it had been decided that SSA would focus steadfastly on only two activities: publishing the Bulletin of the Seismological Society of America ( BSSA ) and holding annual meetings. Perry Byerly, who ran SSA as its elected secretary from 1930 to 1956, institutionalized this maxim in his 1964 published history. It was quoted frequently to me and to anyone who had the temerity to suggest that SSA take on new things. In the early 1970s, funding for nuclear explosion monitoring prompted a great growth in the number of seismologists and seismic installations. The SSA membership and the number of papers in BSSA grew substantially, too. The San Fernando earthquake in 1971 was my first lesson in how funding flows after a disaster. But even as the science expanded, the Society stayed focused for many years …

Biodegradation of the cyclic nitramine explosives RDX, HMX, and CL-20

Cyclic nitramine explosives are synthesized globally mainly as military munitions, and their use has resulted in environmental contamination. Several biodegradation pathways have been proposed, and these are based mainly on end-product characterization because many of the metabolic intermediates are hypothetical and unstable in water. Biodegradation mechanisms for cyclic nitramines include (a) formation of a nitramine free radical and loss of nitro functional groups, (b) reduction of nitro functional groups, (c) direct enzymatic cleavage, (d) alpha-hydroxylation, or (e) hydride ion transfer. Pathway intermediates spontaneously decompose in water producing nitrite, nitrous oxide, formaldehyde, or formic acid as common end-products. In vitro enzyme and functional gene expression studies have implicated a limited number of enzymes/genes involved in cyclic nitramine catabolism. Advances in molecular biology methods such as high-throughput DNA sequencing, microarray analysis, and nucleic acid sample preparation are providing access to biochemical and genetic information on cultivable and uncultivable microorganisms. This information can provide the knowledge base for rational engineering of bioremediation strategies, biosensor development, environmental monitoring, and green biosynthesis of explosives. This paper reviews recent developments on the biodegradation of cyclic nitramines and the potential of genomics to identify novel functional genes of explosive metabolism.

Architecture and critical technologies of seismic information system in CTBT verification

Seismic monitoring is one of the most important approaches for ground-based nuclear explosion monitoring. In order to improve the monitoring capability for low magnitude seismic events, a seismic information system was developed by using the technologies of geographic information system and database. This paper describes the designing and critical technologies of the Seismic Information System in CTBT Verification developed based on ArcGIS and ORACLE platforms. It is a combination of the database storage framework, application programming interface and graphic application software for users to meet their monitoring objectives. Combining the ArcSDE Geodatabase, RDBMS ORACLE and ArcObjects developing technique on COM, not only the multi-sources data has been seamlessly integrated, but also the most functions of ORACLE, for example, consistency, concurrent access, security mechanism, etc, have been reserved. For easy access to the information system we develop two different mechanisms. The first is a menu-driven internal system that is run on NT platforms. The second access mechanism is based on LAN and easily accessible by any web browsers.

Anomalous transparency of the water/air interface for low-frequency sound

Sound transmission through water/air interface is normally weak because of a stark density contrast between the two media. For a monopole sound source, at depth larger than a wavelength, the ratio R of the acoustic power transmitted into the air to the total emitted acoustic power is a small quantity of the order of the ratio of impedances of air and water. Acoustic transparency of the interface is shown to rise dramatically at low frequencies, where depth of the monopole source is small compared to the wavelength, with R increasing by up to 36 dB. Under certain conditions, almost all of the acoustic energy emitted by a low-frequency monopole source underwater is predicted to be radiated into the air rather than into the water. Physically, higher transparency at lower frequencies is due to increasing role of inhomogeneous waves emitted by the source and a destructive interference of fields in water due to the actual and image sources. The anomalous transparency of the water/air interface may have significant implications for generation of low-frequency acoustic noise in the air by bubbles collapsing underwater and for acoustic monitoring and detection of powerful underwater explosions for the purposes of the Comprehensive Nuclear Test Ban Treaty.

Monitoring of seismic events from a specific source region using a single regional array: A case study

In the monitoring of earthquakes and nuclear explosions using a sparse worldwide network of seismic stations, it is frequently necessary to make reliable location estimates using a single seismic array. It is also desirable to screen out routine industrial explosions automatically in order that analyst resources are not wasted upon detections which can, with a high level of confidence, be associated with such a source. The Kovdor mine on the Kola Peninsula of NW Russia is the site of frequent industrial blasts which are well recorded by the ARCES regional seismic array at a distance of approximately 300 km. We describe here an automatic procedure for identifying signals which are likely to result from blasts at the Kovdor mine and, wherever possible, for obtaining single array locations for such events. Carefully calibrated processing parameters were chosen using measurements from confirmed events at the mine over a one-year period for which the operators supplied Ground Truth information. Phase arrival times are estimated using an autoregressive method and slowness and azimuth are estimated using broadband f{-}k analysis in fixed frequency bands and time-windows fixed relative to the initial P-onset time. We demonstrate the improvement to slowness estimates resulting from the use of fixed frequency bands. Events can be located using a single array if, in addition to the P-phase, at least one secondary phase is found with both an acceptable slowness estimate and valid onset-time estimate. We evaluate the on-line system over a twelve month period; every event known to have occured at the mine is detected by the process and 32 out of 53 confirmed events were located automatically. The remaining events were classified as “very likely” Kovdor events and were subsequently located by an analyst. The false alarm rate is low; only 84 very likely Kovdor events were identified during the whole of 2003 and none of these were subsequently located at a large distance from the mine. The location accuracy achieved automatically by the single-array process is remarkably good, and is comparable to that obtained interactively by an experienced analyst using two-array observations. The greatest problem encountered in the single array location procedure is the difficulty in determining arrival times for secondary phases, given the weak Sn phase and the complexity of the P-coda. The method described here could be applied to a wide range of locations and sources for which the monitoring of seismic activity is desirable. The effectiveness will depend upon the distance between source and receiver, the nature of the seismic sources and the level of regional seismicity.

Long-range propagation and scattering of low-frequency sound pulses in the middle atmosphere

A short historical review and an analysis of the current status of both theoretical and experimental studies of long-range sound propagation in the atmosphere are given. Basic results are given on the atmospheric fine-layered structure that significantly affects the infrasonic pulse propagation and scattering in the lower and middle atmosphere. The effect of time variations (seasonal changes, tides, and both planetary and internal gravity waves) in the effective acoustic speed profile on the characteristics of infrasonic signals from different pulsed sources is discussed. The results of the studies of partial reflection (scattering) of low-frequency acoustic pulses from the fine-layered inhomogeneities of the middle atmosphere are presented. The results of the corresponding theoretical studies are also given. The potentialities of the method of long-range acoustic sounding of large-scale anisotropic turbulence in the middle atmosphere are discussed. The problems of infrasonic monitoring of nuclear low-energy explosions are also considered.