ALBERT

Description: Ataxia telangiectasia (A-T), a rare autosomal recessive disorder characterized by progressive cerebellar degeneration and a greatly increased incidence of cancer among other symptoms, is caused by a defective or missing ataxia telangiectasia mutated (ATM) gene. The ATM protein has roles in DNA repair and in the regulation of reactive oxygen...

Description: We studied seismic-wave generation from five small (60–122 kg) fully contained explosions detonated in Barre Granite as a part of the New England Damage Experiment (NEDE). The explosions were conducted using three types of explosives with different velocities of detonation (VOD): black powder, ammonium nitrate fuel oil (ANFO) emulsion, and composition B (COMP-B). Empirical evidence suggests that the low VOD explosives produce more shear-wave energy than high VOD explosives. The proposed mechanisms to explain this effect include: (a) inhibition of gas-driven fracture propagation by thicker pulverized zone for high VOD explosions, and (b) fracture toughness increase at higher loading rate. The main objective of the experiment was to study differences in shear-wave generation between different types of explosives, and to determine the likely mechanism responsible for these differences. Seismic amplitude analysis revealed that COMP-B releases more energy and larger amplitude P waves for the same weight of explosives, while producing smaller amplitude S waves. Furthermore, large radial cracks were observed on the surface after the ANFO and black powder shots, while there was no surface fracturing after the COMP-B shots. Thus, longer fractures correlate with higher S -wave amplitudes. However, drilling into the source region indicates that high VOD explosions may actually produce a smaller pulverized zone, which means that fracture inhibition is a less plausible explanation. Therefore we hypothesize that increase in loading rate, in combination with shorter impulse duration for high VOD explosives, inhibits fracture processes, and subsequently reduced S -wave radiation.

Description: We studied seismic body-wave generation from four fully contained explosions of approximately the same yields (68 kg of TNT equivalent, where TNT stands for trinitrotoluene) conducted in homogeneous granite in Barre, Vermont. The explosions were detonated using three types of explosives with different velocities of detonation: black powder (BP), ammonium nitrate fuel oil/emulsion (ANFO), and composition B (COMP B). The main objective of the experiment was to study differences in seismic-wave generation among different types of explosives and to determine the mechanism responsible for these differences. The explosives with slow burn rate (BP) produced lower P -wave amplitude and corner frequency, which resulted in lower seismic efficiency (0.21%) in comparison with high burn rate explosives (1.3% for ANFO and 1.9% for COMP B). The seismic efficiency estimates for ANFO and COMP B agree with previous estimates for nuclear explosions. The body-wave radiation pattern is consistent with an isotropic explosion with an added azimuthal component caused by vertical tensile fractures oriented along pre-existing microfracturing in the granite, although the complexities in the P - and S -wave radiation patterns suggest that more than one fracture orientation could be responsible for their generation. Analysis of the S / P amplitude ratios suggests that a significant fraction of the shear-wave energy can be explained by opening of the tensile fractures and spall.

Description: Love waves have the potential to aid in discrimination for anomalous explosion events. We develop a calibrated mathematical formulation for an explosion discriminant that combines Rayleigh- and Love-wave magnitude values and employs an error model that correctly partitions variances among events and stations separately. The discriminant is calibrated using a global data set of 124 earthquakes and 26 nuclear explosions and applied to the May 2009 Democratic Republic of North Korea (DPRK) announced nuclear test, as well as the calibration data set. All 26 explosions were correctly identified; only 6 earthquakes were incorrectly identified as explosions. Compared to an analogous treatment using only Rayleigh data, the combined discriminant improves the DPRK event p -value only nominally but reduces the number of false positives in the calibration data set by 70%, with no additional false negatives. While not dramatically improving the discrimination power for anomalous events, such as the 2009 DPRK test, the combined discriminant proposed here offers improved screening capabilities for typical events. Online Material: Earthquake and explosion calibration data set.

Description: The May 2012 HUMBLE REDWOOD III (HRIII) experiment series in New Mexico provides a unique dataset to study surface-wave generation from explosions conducted above and underground for different rock types. Four 90.6 kg trinitrotoluene-equivalent explosions were detonated either at 2 m height-of-burst (HOB) or 7 m depth-of-burial (DOB) at separate alluvium and limestone test sites. For the alluvium site, data from a temporary seismoacoustic network show that fundamental-mode surface waves ( ) from the 7 m DOB in-alluvium shot were four to five times larger than the above-alluvium shot. The amplitudes from the 7 m DOB limestone shot were 15 times larger than recorded from the collocated 2 m HOB shot. To model these differences in , we generated 1D velocity models for both test sites using observed surface-wave dispersion. We considered two different methods for synthetic seismogram generation. For the aboveground shots, we have coupled near-field blast wave pressures and shapes with source medium properties to model seismic data at distance. For the underground shots, we use explosion source theory to estimate a moment for scaling explosion synthetics. For both above and underground shots, the synthetics provide excellent fits to the observed 1–5 Hz data. This modeling provides a viable technique to predict peak particle velocities for surface and aboveground explosions in different rock types that can be used to estimate combined seismoacoustic yields. Online Material: Movies of four explosions studied in this paper.

Description: A mine blast is typically composed of many individual explosions detonated in a temporal and spatial grid, a process called delay firing. A recent experiment at a granite quarry in Massachusetts included detonation of a delay-fired (DF) mining blast within 250 m of a single-fired (SF) explosion. The DF blast consisted of 48 holes detonated over 0.495 s. It produced longer duration Rayleigh waves with envelope functions that peaked later than Rayleigh waves generated by the SF explosion. Measured group velocity dispersion curves for recordings of the DF blast were slower than the estimates for the SF explosion, and with larger differences noted at near-source stations. Using a formula derived initially by Ben-Menahem (1961) for dynamically rupturing fault lines, we correct the dispersion curves using an initial group delay of 0.32 s. We demonstrate that for delay-firing patterns of ~0.5 s, the effect of the initial group delay is not significant beyond 25 km; however, for longer-duration blasts, the effect could be observed at distances beyond 100 km. Mine blast firing patterns should be considered prior to using the resulting dispersion curves for crustal structure determination. Online Material: MPEG movies of the DF and SF shots.

Description: The traditional M s : m b discrimination method is routinely used for distinguishing between earthquakes and explosions within dense networks, but there is a need to improve discrimination at smaller magnitudes; therefore, we need magnitude scales that can successfully be applied to data from sparse networks. We developed a unified Rayleigh- and Love-wave magnitude scale ( M s U) that is designed to maximize available information from single stations and then combine magnitude estimates into network averages. By combining Love- and Rayleigh-wave amplitudes, we minimize the effect of earthquake radiation patterns from sparse networks, thereby improving discrimination between earthquakes and explosions. M s U is built from M s ( V MAX ) ( Russell, 2006 ) and is calculated from Love and Rayleigh waves that are narrowband filtered and corrected for propagation and source effects at periods between 8 and 25 s to find filter bands of maximum energy propagation. The data are also corrected for censoring effects at the station level, because either Rayleigh or Love waves may be below the signal-to-noise ratio threshold at a given period. We applied M s U to 39 earthquakes (3.21〈 M w 〈5.08) located in the Yellow Sea and Korean Peninsula region, as well as to the three North Korean nuclear tests (4.1〈 m b 〈5.1). By using M s U: m b as a discriminant, there is an increase in the separation of small magnitude earthquakes and explosions in sparse networks and a significant reduction in outliers, as shown in the application from the Korean Peninsula. This research addresses the theory, methods, and capability of M s U as a discriminant. Online Material: Detailed spectral analysis and M s U censoring algorithm, and figures of filter specifications.

Description: The Russell surface-wave magnitude formula, developed in Part I of this two-part article, and the M (sub s) (VMAX) measurement technique, discussed in this article, provide a new method for estimating variable-period surface-wave magnitudes at regional and teleseismic distances. The M (sub s) (VMAX) measurement method consists of applying Butterworth bandpass filters to data at center periods between 8 and 25 sec. The filters are designed to help remove the effects of nondispersed Airy phases at regional and teleseismic distances. We search for the maximum amplitude in all of the variable-period bands and then use the Russell formula to calculate a surface-wave magnitude. In this companion article, we demonstrate the capabilities of the method by using applications to three different datasets. The first application utilizes a dataset that consists of large earthquakes in the Mediterranean region. The results indicate that the M (sub s) (VMAX) technique provides regional and teleseismic surface-wave magnitude estimates that are in general agreement except for a small distance dependence of -0.002 magnitude units per degree. We also find that the M (sub s) (VMAX) estimates are less than 0.1 magnitude unit different than those from other formulas applied at teleseismic distances such as Rezapour and Pearce (1998) and Vanek et al. (1962). In the second and third applications of the method, we demonstrate that measurements of M (sub s) (VMAX) versus m (sub b) provide adequate separation of the explosion and earthquake populations at the Nevada and Lop Nor Test Sites. At the Nevada Test Site, our technique resulted in the misclassification of two earthquakes in the explosion population. We also determined that the new technique reduces the scatter in the magnitude estimates by 25% when compared with our previous studies using a calibrated regional magnitude formula. For the Lop Nor Test Site, we had no misclassified explosions or earthquakes; however, the data were less comprehensive. A preliminary analysis of Eurasian earthquake and explosion data suggest that similar slopes are obtained for observed M (sub s) (VMAX) versus m (sub b) data with m (sub b) 〈5. Thus the data are not converging at lower magnitudes. These results suggest that the discrimination of explosions from earthquakes can be achieved at lower magnitudes using the Russell (2006) formula and the M (sub s) (VMAX) measurement technique.