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

Zucca, J.J.; Walter, William R.; Rodgers, Arthur R.; Richards, Paul G.; Pasyanos, Michael E.; Myers, Stephen C.; Lay, Thorne; Harris, Dave; Antoun, T.

doi:10.1785/gssrl.80.1.31

Cited by 4 publications

(2 citation statements)

References 42 publications

(24 reference statements)

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“…Although the past years have seen considerable progress in developing global 3-D velocity models that give accurate traveltime predictions (e.g. Myers & Schultz 2000;Ritzwoller et al 2003;Yang et al 2004;Morozov et al 2005;Murphy et al 2005;Reiter et al 2005;Flanagan et al 2007;Zucca et al 2009;Myers et al 2010), Figure 18. (Continued.…”

Section: Discussion a N D C O N C L U S I O N Smentioning

confidence: 99%

Improved location procedures at the International Seismological Centre

Bondár¹,

Storchak²

2011

Geophysical Journal International

200

138

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S U M M A R YThe International Seismological Centre (ISC) is a non-governmental, non-profit organization with the primary mission of producing the definitive account of the Earth's seismicity. The ISC Bulletin covers some 50 yr of seismicity. The recent years have seen a dramatic increase both in the number of reported events and especially in the number of reported phases, owing to the ever-increasing number of stations worldwide. Similar ray paths will produce correlated traveltime prediction errors due to unmodelled heterogeneities in the Earth, resulting in underestimated location uncertainties, and for unfavourable network geometries, location bias. Hence, the denser and more unbalanced the global seismic station coverage becomes, the less defensible is the assumption (that is the observations are independent), which is made by most location algorithms.To address this challenge we have developed a new location algorithm for the ISC that accounts for correlated error structure, and uses all IASPEI standard phases with a valid ak135 traveltime prediction to obtain more accurate event locations. In this paper we describe the new ISC locator, and present validation tests by relocating the ground truth events in the IASPEI Reference Event List, as well as by relocating the entire ISC Bulletin.We show that the new ISC location algorithm provides small, but consistent location improvements, considerable improvements in depth determination and significantly more accurate formal uncertainty estimates. We demonstrate that the new algorithm, through the use of later phases and testing for depth resolution, considerably clusters event locations more tightly, thus providing an improved view of the seismicity of the Earth.

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Section: Discussion a N D C O N C L U S I O N Smentioning

confidence: 99%

Improved location procedures at the International Seismological Centre

Bondár¹,

Storchak²

2011

Geophysical Journal International

200

138

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“…However, more accurate estimates of epicenters are needed to access the proximity of earthquakes to metropolitan areas and to guide an on-site inspection under the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Zucca et al (2009) outline a plan to develop and implement 3D models in an operational system, and several models of Earth structure have been subsequently developed.…”

Section: Introductionmentioning

confidence: 99%

Improved Regional and TeleseismicP‐Wave Travel‐Time Prediction and Event Location Using a Global 3D Velocity Model

Myers¹,

Simmons²,

Johannesson³

et al. 2015

Bulletin of the Seismological Society of America

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A global validation dataset of 116 seismic events and 20,977 associated Pn and P arrivals is used to assess travel-time prediction and event location accuracy for the global-scale, 3D, P-wave velocity model called LLNL-G3Dv3 (Simmons et al., 2012). Strong regional trends that are observed for ak135 travel-time residuals are largely removed when LLNL-G3Dv3 is used for prediction. The 25th-75th quantile spread of travel-time residuals is reduced by 30%-40% at teleseismic distances, and the spread is reduced by ∼60% at regional distances (< 16°). Epicenter error decreases when more data are used to constrain event locations until more than ∼40 arrivals times are used. At which point, epicenter error reduction tends to plateau. Median epicenter errors for the ak135 and LLNL-G3Dv3 models plateau at ∼8:0 and ∼5:5 km, respectively, for teleseismic P datasets. Median epicenter errors for the ak135 and LLNL-G3Dv3 models plateau at ∼12:0 and ∼4:0 km, respectively, for regional Pn datasets. We demonstrate that spatially correlated travel-time residual errors for the ak135 model lead to increasing epicenter error when ∼40 to ∼100 Pn arrivals are used to constrain the location. The effect of correlated error is mitigated by LLNL-G3Dv3, for which epicenter error steadily decreases to ∼4 km when 100 Pn arrivals are used. The median area of 0.95 epicenter probability bounds for ak135 and LLNL-G3Dv3 are 1811 and 758 km 2 , respectively. The ak135 ellipses are inflated to achieve the desired rate of true events occurring inside the probability region, whereas LLNLG3Dv3 error ellipses based on empirical residual distributions cover the true location at the expected rate because location bias is minimal.

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SPiRaL: a multiresolution global tomography model of seismic wave speeds and radial anisotropy variations in the crust and mantle

Simmons

Myers

Morency

et al. 2021

Geophysical Journal International

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Summary SPiRaL is a joint global-scale model of wave speeds (P and S) and anisotropy (vertical transverse isotropy) variations in the crust and mantle. The model is comprised of >2.1 million nodes with five parameters at each node that capture velocity variations for P- and S-waves traveling at arbitrary directions in transversely isotropic media with a vertical symmetry axis (VTI). The crust (including ice, water, sediments, crystalline layers) is directly incorporated into the model. The default node spacing is approximately 2° in the lower mantle and 1° in the crust and upper mantle. The grid is refined with ∼0.25° minimum node spacing in highly sampled regions of the crust and upper mantle throughout North America and Eurasia. The data considered in the construction of SPiRaL includes millions of body wave travel times (crustal, regional, and teleseismic phases with multiples) and surface wave (Rayleigh and Love) dispersion. A multi-resolution inversion approach is employed to capture long-wavelength heterogeneities commonly depicted in global-scale tomography images as well as more localized details that are typically resolved in more focused regional-scale studies. Our previous work has demonstrated that such global-scale models with regional-scale detail can accurately predict both teleseismic and regional body wave travel times, which is necessary for more accurate location of small seismic events that may have limited signal at teleseismic distances. SPiRaL was constructed to predict travel times for event location and long-period waveform dispersion for seismic source inversion applications in regions without sufficiently tuned models. SPiRaL may also serve as a starting model for full-waveform inversion (FWI) with the goal of fitting waves with periods 10–50 seconds over multiple broad regions (thousands of kilometers) and potentially the globe. To gain insight to this possibility, we simulated waveforms using SPiRaL and independent waveform-based models for comparison. The performance of the travel-time-based SPiRaL model is shown to be on par with regional 3-D waveform-based models in three regions (western United States, Middle East, Korean Peninsula) suggesting SPiRaL may serve as a starting model for FWI over broad regions.

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

Cited by 4 publications

References 42 publications

Improved location procedures at the International Seismological Centre

Improved location procedures at the International Seismological Centre

Improved Regional and TeleseismicP‐Wave Travel‐Time Prediction and Event Location Using a Global 3D Velocity Model

SPiRaL: a multiresolution global tomography model of seismic wave speeds and radial anisotropy variations in the crust and mantle

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