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  • Articles  (37)
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  • 1
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    An Explosion Model Comparison with Insights from the Source Physics Experiments (2013)
    Seismological Society of America (SSA)
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    Publication Date: 2013-10-01
    Description: Seismic spectral models for chemical and nuclear explosions are used in many applications including network modeling and yield estimation. Here we compare the models presented in Denny and Johnson (1991) and Mueller and Murphy (1971) with each other and with new results from the Source Physics Experiments (SPE). We demonstrate analytically the two models are in substantial agreement for large and normally buried explosions, consistent with much of the historic data collected during American and Soviet nuclear testing. However, for small and/or deeply buried explosions, the spectral predictions of the two models can differ significantly. For example, the predicted yield of a 1 km deep, M w  2 nuclear explosion differs by more than a factor of 5; and, for the same moment and depth chemical explosion, the difference is greater than a factor of 10. We compare the models with initial data from the SPE, which include small and overburied chemical explosions. The corner frequency of the one-ton SPE explosion (SPE-2) is slightly higher than the Mueller and Murphy (1971) model and approximately double the Denny and Johnson (1991) model prediction. The absolute moment of the one-tenth ton SPE explosion (SPE-1) is near the Denny and Johnson (1991) prediction and an order of magnitude smaller than the Mueller and Murphy (1971) prediction. The low-frequency moment ratio for SPE-2/SPE-1 is more consistent with the Denny and Johnson (1991) model. The results presented here show the need for an improved explosion source model that can accommodate a wider range of yields and emplacement conditions. Online Material: Moment magnitude, corner frequency, and yield for all geologic media.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 2
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    International Monitoring System Correlation Detection at the North Korean Nuclear Test Site at Punggye-ri with Insights from the Source Physics Experiment (2015)
    Seismological Society of America (SSA)
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    Publication Date: 2015-07-02
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America (SSA)
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  • 3
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    Source Characterization of Underground Explosions from Combined Regional Moment Tensor and First-Motion Analysis (2014)
    Seismological Society of America (SSA)
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    Publication Date: 2014-08-08
    Description: In this study, we investigate the 14 September 1988 U.S.–Soviet Joint Verification Experiment nuclear test at the Semipalatinsk test site in eastern Kazakhstan and two nuclear explosions conducted less than 10 years later at the Chinese Lop Nor test site. These events were very sparsely recorded by stations located within 1600 km, and in each case only three or four stations were available in the regional distance range. We have utilized a regional distance seismic waveform method fitting long-period, complete, three-component waveforms jointly with first-motion observations from regional stations and teleseismic arrays. The combination of long-period waveforms and first-motion observations provides a unique discrimination of these sparsely recorded events in the context of the Hudson et al. (1989) source-type diagram. We demonstrate through a series of jackknife tests and sensitivity analyses that the source type of the explosions is well constrained. One event, a 1996 Lop Nor shaft explosion, displays large Love waves and possibly reversed Rayleigh waves at one station, indicative of a large F -factor. We show the combination of long-period waveforms and P -wave first motions are able to discriminate this event as explosion-like and distinct from earthquakes and collapses. We further demonstrate the behavior of network sensitivity solutions for models of tectonic release and spall-based tensile damage over a range of F -factors and K -factors.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 4
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    Source analysis of the Crandall Canyon, Utah, mine collapse (2008)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2008-07-16
    Description: Analysis of seismograms from a magnitude 3.9 seismic event on 6 August 2007 in central Utah reveals an anomalous radiation pattern that is contrary to that expected for a tectonic earthquake and which is dominated by an implosive component. The results show that the seismic event is best modeled as a shallow underground collapse. Interestingly, large transverse surface waves require a smaller additional noncollapse source component that might represent either faulting in the rocks above the mine workings or deformation of the medium surrounding the mine. Seismic moment tensor results for nuclear explosions, explosion and other mining cavity collapses, and tectonic earthquakes are compared, and the separation of the different populations indicates that the seismic moment tensor may be used for source-type discrimination.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Dreger, Douglas S -- Ford, Sean R -- Walter, William R -- New York, N.Y. -- Science. 2008 Jul 11;321(5886):217. doi: 10.1126/science.1157392.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Berkeley Seismological Laboratory, University of California, Berkeley, CA 94720, USA. dreger@seismo.berkeley.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18621662" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Moment Tensor Analysis of Very Shallow Sources (2016)
    Seismological Society of America (SSA)
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    Publication Date: 2016-12-02
    Description: An issue for moment tensor (MT) inversion of shallow seismic sources is that some components of the Green’s functions have vanishing amplitudes at the free surface, which can result in bias in the MT solution. The effects of the free surface on the stability of the MT method become important as we continue to investigate and improve the capabilities of regional full MT inversion for source-type identification and discrimination. It is important to understand free-surface effects on discriminating shallow explosive sources for nuclear monitoring purposes. It may also be important in natural systems that have very shallow seismicity, such as volcanic and geothermal systems. We examine the effects of the free surface on the MT via synthetic testing and apply the MT-based discrimination method to three quarry blasts from the HUMMING ALBATROSS experiment. These shallow chemical explosions at ~10 m depth and recorded up to several kilometers distance represent rather severe source–station geometry in terms of free-surface effects. We show that the method is capable of recovering a predominantly explosive source mechanism, and the combined waveform and first-motion method enables the unique discrimination of these events. Recovering the design yield using seismic moment estimates from MT inversion remains challenging, but we can begin to put error bounds on our moment estimates using the network sensitivity solution technique ( Ford et al. , 2010 ). Online Material: Figures showing synthetic tests for a pure explosion and a composite source at local distances and table of moment tensor components.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 6
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    Relative Surface-wave Amplitude and Phase Anomalies from the Democratic People's Republic Korea Announced Nuclear Tests (2017)
    Wiley
    Details
    Publication Date: 2017-08-31
    Description: We performed relative locations of six event-pairs based on surface-wave (SW) and body-wave (BW) differential travel-times of the 2016-09-09, 2016-01-06, 2013-02-12, and 2009-05-25 announced North Korea nuclear explosions. The SW relative locations for the 2009-05-25 and 2013-02-12 events were inconsistent with the BWs when paired with other events and only the 2016-01-06/2016-09-09 pair was consistent. Apparent SW phase shift is investigated with respect to the BW relative locations. The pairs formed with the 2009-05-25 and 2013-02-12 events, beneath the southeast slope of Mount Mant'ap, have the largest phase shifts and amplitude ratio deviations, whereas the least deviation was from the 2016-01-06 and 2016-09-09 event-pair beneath the mountain peak. Regional moment tensors (MTs) predict the amplitude ratios but do not resolve the relative phase. We find MTs with 10% difference in isotropic and rotated +CLVD can fit both relative phase and amplitude ratios. SW relative locations of highly isotropic and correlated explosion clusters can be affected by topography and small differences in MT.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    mb:Ms Screening Revisited for Large Events (2014)
    Seismological Society of America (SSA)
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    Publication Date: 2014-06-12
    Description: Event screening of large-magnitude events ( M w 5) based on m b : M s is revisited to account for the effect of the source corner frequency relative to the fixed frequencies of the long-period M s and short-period m b . For large events this source effect increases the slope of m b : M s relative to the 1:1 value expected for small events. The effect is demonstrated in the large earthquake m b : M s population and in the behavior of large theoretical explosions that are consistent with the more limited explosion population. The behavior is used to create a more conservative screening criterion that ensures large explosions are not inadvertently screened out by m b : M s , while not appreciably decreasing the number of screened earthquakes. This change also makes the variance of the earthquake and explosion populations more equal, which is of utility in statistical analysis. A slight trend in the explosion population and a case study of two large U.S. underground nuclear tests provide support for adopting a more conservative approach.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 8
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    2D Variations in Coda Amplitudes in the Middle East (2016)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2016-10-08
    Description: Coda amplitudes have proven to be a stable feature of seismograms, allowing one to reliably measure magnitudes for moderate-to-large ( M ≥3) earthquakes over broad regions. Because smaller ( M 〈3) earthquakes are only recorded at higher frequencies for which we find larger interstation scatter, amplitude and magnitude estimates for these events are more variable, regional, and path dependent. In this article, we investigate coda amplitude measurements in the Middle East for 2D variations in attenuation structure. One critical aspect of this effort is characterizing the propagation term to include scattering, which allows us to use amplitudes out to longer distances and later in the coda. We perform a tomographic inversion and find that the recovered attenuation structure is both very similar to the attenuation structure derived from direct phases and also reflective of the tectonic structure of the region. We then apply the 2D attenuation corrections to several hundred events in the region and find marked improvements to our magnitude estimates, as measured by interstation scattering, resulting in standard deviations of less than 0.025 magnitude units at all frequencies. The improvements are greatest at high frequencies, which will have the largest effect on smaller magnitude events.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 9
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    Initial Global Seismic Cross-Correlation Results: Implications for Empirical Signal Detectors (2015)
    Seismological Society of America (SSA)
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    Publication Date: 2015-01-30
    Description: In this work, we cross-correlated waveforms in a global dataset consisting of over 310 million waveforms from nearly 3.8 million events recorded between 1970 and 2013 for two purposes: to better understand the nature of global seismicity and to evaluate correlation as a technique for automated event processing. We found that about 14.5% of the events for which we have at least one waveform correlated with at least one other event at the 0.6 or higher level. Within the geographic regions where our waveform holdings are complete or nearly complete, that fraction rose to nearly 18%. Moreover, among the events for which we had one or more seismograms recorded at distances less than 12°, the fraction of correlated events was much higher, often exceeding 50%. These results imply that global seismicity contains a large number of repeating events, that is, events that are sufficiently similar to each other to have correlated waveforms over the time period spanned by our dataset. These results are very encouraging for using correlation in aspects of automated event processing. It is well known that because of the strongly implied similarity of the sources of correlated signals, they can be used as empirical signal detectors (ESD) to detect, locate, and identify an event using as few as one channel. Our results are very encouraging for using correlation and perhaps other forms of ESD for regional network processing and continental global processing because, for example, nearly all continental seismicity (99%) is within 12° of at least one International Monitoring System station.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 10
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    Exploiting Regional Amplitude Envelopes: A Case Study for Earthquakes and Explosions in the Korean Peninsula (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-10-01
    Description: We introduce a new method to use narrowband regional amplitude envelopes for event analysis. Building on the success of the coda-wave method, we construct synthetic template envelopes that attempt to fit the entire waveform, including multiple direct phases and their coda, across a broad frequency band. The method makes use of our understanding of earthquake and explosion source models, regional wave propagation, and the relationship between direct amplitudes and their respective codas. We demonstrate the power of the method by examining earthquake and nuclear explosions in the Korean Peninsula at regional distance stations MDJ (Mudangjing, China) and TJN (Taejon, South Korea). In order to implement the method, however, we need to account for propagation through the use of an attenuation model for the region, which we have developed, in addition to an empirical correction to provide for unaccounted effects in the direct-to-coda transfer functions. Under the assumption that our explosion and attenuation models and the empirically obtained P -to- P -coda and S -to- S -coda transfer functions are correct, we determine that the 2006 test by the Democratic People’s Republic of Korea (DPRK) is consistent with a yield between 200 and 800 tons and a depth between 20 and 300 m, with our best fit at 500 tons at a depth of 100 m. Similarly, the 2009 DPRK test is consistent with a yield range of 1–5 kt and a depth range of 70–600 m, with our best fit at 2 kt at a depth of 200 m.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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