13 results on '"Richards, Paul"'
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2. TOWARD A NEW TEST BAN REGIME
- Author
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Richards, Paul G. and Lindh, Allan
- Published
- 1987
3. MONITORING FOR NUCLEAR EXPLOSIONS.
- Author
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Richards, Paul G. and Kim, Won-Young
- Subjects
- *
NUCLEAR weapons , *NUCLEAR weapons testing , *WEAPONS of mass destruction , *NUCLEAR arms control , *NUCLEAR disarmament , *SEISMOLOGY - Abstract
The article explains that systems are in place that can detect a nuclear weapon test of a kiloton or greater anywhere on the Earth, making it impossible for any nation to test nuclear devices without the world's knowledge. Scientists have accomplished this through the use of seismic technologies. The author also mentions U.S. President Barack Obama's intentions to ratify the Comprehensive Nuclear-Test-Ban Treaty. INSETS: How to Tell a Blast from a Crash;How Monitoring for the Treaty Covers Earth;WHAT GOOD IS A TEST?;Fifty Years of Nuclear Testing and Monitoring
- Published
- 2009
- Full Text
- View/download PDF
4. Seismological Constraints on Proposed Low-Yield Nuclear Testing in Particular Regions and Time Periods in the Past
- Author
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Schaff, David P., Kim, Won-Young, and Richards, Paul G.
- Subjects
Seismology--Data processing ,Nuclear explosions ,Seismology - Abstract
We have attempted to detect seismic signals from small explosions in North Korea on five specific days in 2010 that feature in scenarios proposed by De Geer. We searched the seismic data recorded by station MDJ in northeastern China, applying three-component cross-correlation methods using signals from known explosions as templates. We assess the capability of this method of detection, and of simpler methods, all of which failed to find seismic signals that would be expected if De Geer's scenarios were valid. We conclude that no well-coupled underground explosion above about a ton occurred near the North Korea test site on these five days and that any explosion would have to be very small (local magnitude less than about 2) to escape detection.
- Published
- 2012
- Full Text
- View/download PDF
5. The history and outlook for seismic monitoring of nuclear explosions in the context of the Comprehensive Nuclear-Test-Ban Treaty.
- Author
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Richards, Paul G.
- Subjects
NUCLEAR explosions ,EARTHQUAKE hazard analysis ,ARMS control ,COMPREHENSIVE Nuclear-Test-Ban Treaty - Abstract
Modern methods of nuclear-explosion monitoring are vastly more capable than they were when underground nuclear testing began in the late 1950s, in part because a cycle of improvements in explosion monitoring in the 1960–80 period led to improvements in monitoring for earthquakes and other phenomena, which then led to a general growth in monitoring assets that in turn has been applied back to explosion monitoring. Practical experiences in nuclear-explosion monitoring, acquired during the era of active testing prior to finalization of the CTBT text in 1996, laid the basis for monitoring in support of this arms-control initiative. This article elaborates on the future of nuclear-test-monitoring technology, which can build upon an additional and remarkable growth of general monitoring assets that began in the 1990s, largely unrelated to the specifics of nuclear-test monitoring. A new cycle of improvements in earthquake monitoring is likely to improve monitoring for explosions. While it is not easy to quantify the degree of monitoring improvement afforded by such new assets, an example from North Korea indicates the improvement can be substantial. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
6. Comprehensive Nuclear-Test-Ban Treaty Seismic Monitoring: 2012 USNAS Report and Recent Explosions, Earthquakes, and Other Seismic Sources.
- Author
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Richards, Paul G.
- Subjects
- *
NUCLEAR weapons testing , *SEISMOLOGY , *ARMS control treaties , *TREATY compliance ,COMPREHENSIVE Nuclear-Test-Ban Treaty - Abstract
A comprehensive ban on nuclear explosive testing is briefly characterized as an arms control initiative related to the Non-Proliferation Treaty. The work of monitoring for nuclear explosions uses several technologies of which the most important is seismology--a physics discipline that draws upon extensive and ever-growing assets to monitor for earthquakes and other ground-motion phenomena as well as for explosions. This paper outlines the basic methods of seismic monitoring within that wider context, and lists web-based and other resources for learning details. It also summarizes the main conclusions, concerning capability to monitor for test-ban treaty compliance, contained in a major study published in March 2012 by the US National Academy of Sciences. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
7. Improvements in magnitude precision, using the statistics of relative amplitudes measured by cross correlation.
- Author
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Schaff, David P. and Richards, Paul G.
- Subjects
- *
EARTHQUAKE magnitude , *AMPLITUDE estimation , *CROSS correlation , *SEISMOLOGY , *RANDOM noise theory , *SIGNAL-to-noise ratio - Abstract
Standard processing of seismic events for reporting in bulletins is usually done one-at-a time. State-of-the-art relative event methods, often involving cross correlation, are increasingly used and have improved estimates of event parameters for event detection, location and magnitude. This is because relative event techniques can simultaneously reduce measurement error and effects of model error. We show how cross correlation can be used to assign relative magnitudes for neighbouring seismic events distributed over a large region in east Asia and quantify to what extent the uncertainty in these values increases as waveform similarity breaks down. We find that cross correlation works well for magnitude comparison of two events when it is expected that they generate very similar signals even if these may be almost buried in large amounts of noise. This may be the case when investigating repeating earthquakes or nuclear explosions within a few kilometres of each other. Cross correlation is the optimal detector in these cases assuming noise is white and Gaussian, and also provides the least-squares solution for the relative amplitudes. However, when the waveform similarity of the underlying signals breaks down, due to interevent separation distance, source time function differences or focal mechanism differences, these assumptions are no longer valid and a bias is introduced into the relative magnitude measurement. This bias due to degradation of waveform similarity is modelled here with synthetics and an analytic expression for it is derived based on three terms—the cross-correlation coefficient (CC), and the signal-to-noise ratio (SNR) of the larger and smaller events. The analytic expression is a good match to the observed bias in the data. If the equation for relative magnitude is rewritten to correct for the bias due to the CC, a new equation results which is simply the log of the ratio of the L2 norms. The bias due to SNRs is still present because the observed waveforms inevitably contain both signal and noise. However, this bias is predicted to be minimal for typical detection thresholds. Making measurements of the ratio of the L2 norms is shown to remove the bias due to degradation of waveform similarity for real data. The scatter of these cross-correlation measurements of relative magnitude is much less than those obtained by differencing magnitudes in a traditional catalogue. Of 14 025 events in and near China, 34 per cent had over an order of magnitude reduction in the median standard deviation (0.0342 magnitude units) as compared to the estimated scatter in the catalogue (0.3454 magnitude units). And 78 per cent of the events show a factor 3 improvement or better in the precision of relative event size measured as the ratio of the L2 norms as compared to the precision of the catalogue for relative magnitudes. These results suggest that the ratio of the L2 norms is an appropriate measure of relative magnitudes for general seismicity of a monitoring region, when there is significant waveform dissimilarity for neighbouring events. This measure maintains a higher degree of measurement precision as compared to the catalogue. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
8. The Applicability of Modern Methods of Earthquake Location.
- Author
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Richards, Paul G., Waldhauser, Felix, Schaff, David, and Won-Young Kim
- Subjects
- *
SEISMIC event location , *EARTHQUAKES , *SEISMOLOGICAL stations , *SEISMOLOGY , *METHODOLOGY - Abstract
We compare traditional methods of seismic event location, based on phase pick data and analysis of events one-at-a-time, with a modern method based on cross-correlation measurements and joint analysis of numerous events. In application to four different regions representing different types of seismicity and monitored with networks of different station density, we present preliminary results indicating what fraction of seismic events may be amenable to analysis with modern methods. The latter can supply locations ten to a hundred times more precise than traditional methods. Since good locations of seismic sources are needed as the starting point for so many user communities, and potentially can be provided due to current improvements in easily-accessible computational capability, we advocate wide-scale application of modern methods in the routine production of bulletins of seismicity. This effort requires access to waveform archives from well-calibrated stations that have long operated at the same location. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
9. 3D First-Arrival Regional Calibration Model of Northern Eurasia.
- Author
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Morozov, Igor B., Morozova, Elena A., Smithson, Scott B., Richards, Paul G., Khalturin, Vitaly I., and Solodilov, Leonid N.
- Subjects
SEISMOLOGY ,TREATIES ,MATHEMATICAL models ,THREE-dimensional imaging ,SEISMIC waves ,CALIBRATION - Abstract
Seismological monitoring of the Comprehensive Test Ban Treaty (CTBT) requires detailed knowledge of travel-time characteristics of seismic phases across large areas. We use first-arrival travel times from several of Russian Deep Seismic Sounding (DSS) profiles, primarily those from Peaceful Nuclear Explosions (PNEs), to construct a 3D regional travel-time model of northern Eurasia. The method used, which can be viewed as a generalization of the existing regionalization techniques, is based on apparent-velocity-based spatial interpolation of the travel times picked from DSS records. The resulting travel-time field is described in terms of an apparent velocity model in the 3D space of geographic coordinates and ray parameter. In the travel-time calibration, this model could be used to construct approximate source-specific station correction surfaces for any location within the region and also as a region-specific reference model to be used as a background for further calibration effort. This approach allows incremental refinement of the model as additional travel-time data become available. By converting the travel-time model into depth, a 3D regional velocity model is obtained, providing a description of the general features of the upper mantle in northern Eurasia. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
10. Reference Events for Regional Seismic Phases at IMS Stations in China.
- Author
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Waldhauser, Felix and Richards, Paul G.
- Subjects
SEISMOLOGY ,GEOPHYSICS ,EARTHQUAKES ,EARTH movements ,GEOLOGY - Abstract
Seismic-event location within the context of monitoring the Comprehensive Nuclear-Test-Ban Treaty entails a priori knowledge of the travel time of seismic phases for a given source to stations of the International Monitoring System (IMS). Such travel-time information (or ground truth, GT) is provided empirically by seismic reference events, events that have well-determined hypocenter locations (epicenters typically known to ± 5 km with high confidence) and origin times. In this study we present new reference events for the calibration of six seismic stations of the IMS in China, a region with high seismic activity. We use the Annual Bulletin of Chinese Earthquakes, which lists about 1000 earthquakes in and near China each year with consistent phase picks at regional stations, to determine precise relative earthquake locations from double-difference cluster analysis. The resulting high-resolution image of active faulting at seismogenic depths in areas of dense seismicity is correlated with the tectonic structure derived from mapped fault information at the surface to validate the absolute locations. We generated 59 reference events with M ≥3.5, distributed in six clusters in central and eastern China, and recorded by at least one of the six IMS stations. The scatter in relative travel-time residuals is reduced from 1.28 sec before to 0.61 sec after relocation, consistent with the relocated positions of the events. The degree of correlation between seismicity structure and well-characterized fault data indicates that, in four clusters, the locations of the new reference events are accurate to within 5 km (GT5), and in two clusters within 10 km (GT10). [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
11. Inner Core Differential Motion Confirmed by Earthquake Waveform Doublets.
- Author
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Zhang, Jian, Song, Xiaodong, Li, Yingchun, Richards, Paul G., Sun, Xinlei, and Waldhauser, Felix
- Subjects
- *
EARTHQUAKES , *SEISMOLOGY , *ISLANDS , *NATURAL disasters , *GEOPHYSICS - Abstract
We analyzed 18 high-quality waveform doublets with time separations of up to 35 years in the South Sandwich Islands region, for which the seismic signals have traversed the inner core as PKP(DF). The doublets show a consistent temporal change of travel times at up to 58 stations in and near Alaska, and they show a dissimilarity of PKP(DF) coda. Using waveform doublets avoids artifacts of earthquake mislocations and contamination from small-scale heterogeneities. Our results confirm that Earth's inner core is rotating faster than the mantle and crust at about 0.3° to 0.5° per year. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
12. An Asperity Model of Large Earthquake Sequences
- Author
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Thorne Lay, Hiroo Kanamori, Simpson, David W., and Richards, Paul G.
- Subjects
geography ,Transverse plane ,geography.geographical_feature_category ,Subduction ,Trench ,Context (language use) ,Submarine canyon ,Fault model ,Fault (geology) ,Geology ,Seismology ,Asperity (materials science) - Abstract
The variation in maximum rupture extent of large shallow earthquakes in circum-Pacific subduction zones is interpreted in the context of the asperity model of stress distribution on the fault plane. Comparison of the historic record of large earthquakes in different zones indicates that four fundamental categories of behavior are observed. These are: (1) the Chile-type regular occurrence of great ruptures spanning more than 500 km; (2) the Aleutians-type variation in rupture extent with occasional ruptures up to 500 km long, and temporal clustering of large events; (3) the Kurile-type repeated failure over a limited zone of 100–300 km length in isolated events; and (4) the Marianas-type absence of large earthquakes. Southern Chile, Alaska, Southern Kamchatka, and possibly the Central Aleutians are grouped in the first category. The Rat Island portion of the Aleutians, Colombia, Southwest Japan, and the Solomon Islands zones demonstrate the temporal variation of rupture length and multiple earthquake sequences that characterize category 2. The New Hebrides and Middle America have earthquake clustering on a more moderate scale, and are intermediate between categories 2 and 3. Category 3 includes the Kurile Islands, Northeast Japan, Peru and Central Chile. Zones lacking large earthquakes (category 4) include the Marianas, Izu-Bonin, and large portions of Tonga-Kermadec. By loosely grouping each subduction zone into these categories and comparing the general range in behavior with a simple fault model, which is used in a numerical simulation, the parameters governing large earthquake development are clarified. Interpretation of the four categories in terms of asperity distribution and interaction permits some inferences of the nature of stress distribution in particular zones. Two factors appear to dominate in the development of large earthquake failure zones; the nature and degree of coupling on the fault contact, and the extent of lateral segmentation of the subduction zone by transverse stress barriers. Strong coupling and uniform stress distribution on the fault plane produces larger events, whereas more heterogeneous stress distributions produce smaller ruptures and temporal variation in rupture length. Segmentation of the subduction zone that may result in stress barriers affecting rupture length is produced by subduction of transverse structures such as aseismic ridges, and is reflected by submarine canyons and geometric variations in trench configuration.
- Published
- 2013
13. The Nature of Seismicity Patterns Before Large Earthquakes
- Author
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Hiroo Kanamori, Simpson, David W., and Richards, Paul G.
- Subjects
Tectonics ,geography ,geography.geographical_feature_category ,Event (relativity) ,Earthquake prediction ,Geophysics ,Induced seismicity ,Fault (geology) ,Seismology ,Geology ,Foreshock ,Asperity (materials science) ,Shock (mechanics) - Abstract
Various seismicity patterns before major earthquakes have been reported in the literature. They include foreshocks (broad sense), preseismic quiescence, precursory swarms, and doughnut patterns. Although many earthquakes are preceded by all, or some, of these patterns, their detail differ significantly from event to event. In order to examine the details of seismicity patterns on as uniform a basis as possible, we made space-time plots of seismicity for many large earthquakes by using the NOAA and JMA catalogs. Among various seismicity patterns, preseismic quiescence appears most common, the case for the 1978 Oaxaca earthquake being the most prominent. Although the nature of other patterns varies from event to event, a common physical mechanism may be responsible for these patterns; details of the pattern are probably controlled by the tectonic environment (fault geometry, strain rate) and the heterogeneity of the fault plane. Here a simple asperity model is introduced to explain these seismicity patterns. In this model, a fault plane with an asperity is divided into a number of subfaults. The subfaults within the asperity are, on the average, stronger than those in the surrounding weak zone. As the tectonic stress increases, the subfaults in the weak zone break in the form of background small earthquakes. If the frequency distribution of the strength of the subfaults has a sharp peak, a precursory swarm occurs. By this time, most of the subfaults in the weak zone are broken and the fault plane becomes seismically quiet. As the tectonic stress increases further, eventually the asperity breaks and sympathetic displacement occurs on the entire fault zone in the form of the main shock. Foreshocks do or do not occur depending upon the distribution of the strength of the subfaults within the asperity. Since the spatio-temporal change in the stress on the fault plane is most likely to dictate the change in seismicity patterns, detailed analysis of seismicity patterns would provide a most direct clue to the state of stress in the fault zone. However, because of the large variation from event to event, seismicity pattern alone is not a definitive tool for earthquake prediction; measurements of other physical parameters such as the spectra, the mechanism and the wave forms of the background events should be made concurrently.
- Published
- 2013
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