Phenomenology Research Using Past Nevada Test Site Explosion and Earthquake Data
We use regional waveform data from the Nevada Test Site (NTS) to investigate phenomenological relationships between recorded amplitude and explosion yield as well as test regional depth estimation procedures. Our goal is to better understand the performance of seismic observables in other regions of monitoring interest, especially at small magnitudes (m{sub b}<<4.5). Some of the topics we are studying include: stable yield estimation, depth estimation, and M{sub g}:m{sub b} performance. We use Lawrence Livermore National Laboratory's NTS explosion database, which consists of several hundred events ranging from {approx}200 to {approx}1500-m depth and yields ranging from a few tenths of a kiloton to the megaton range. In addition to the broadband explosion data, we have a large dataset of well-located earthquakes on the test site with depths ranging from 2 to 17 km and magnitudes ranging between M{sub w}1.5 and 5.7. For yield estimation the relation between teleseismic body wave magnitude (mb) and nuclear explosion yield has been studied extensively over the past several decades for a number of test sites for large (>1 kt) explosions. In this paper we will look at broadband coda, P{sub g,} and L{sub g} from over 260 nuclear explosions to study yield estimation capability by comparing F-factors. For monitoring compliance with a CTBT, small events that are recorded only at regional distances will be used to estimate magnitude and equivalent yield, Past coda studies show that coda-derived magnitudes of earthquakes and explosions are more stable than any direct phase method, including mb(Lg). In fact, single-station coda measurements can be equivalent to a network average of at least ten direct phase measurements over a broad range of frequencies. In regions where the depth estimate is poorly constrained, other regional methods have been proposed to estimate depth. These include time-domain measures of P-wave complexity, cepstral peaking, and more recently spectral peaking from R{sub g}-to-S scattering. Myers et al. (1999) and Mayeda and Walter (1996) showed that strong spectral peaking in the S-wave and coda were likely due to R{sub g}-to-S scattering in the near-source region. We propose a side-by-side comparison of these techniques in a region with excellent ground truth, namely NTS. We will investigate to what extent cepstral peaking, coda spectra peaking, and complexity provide a reliable depth estimate. Finally, a number of large regional studies computing surface wave dispersion curves throughout the globe will be used to push the M{sub g} measurements to smaller magnitude by the use of phase-matched filters. For larger teleseismically recorded events, we will test to see if the M{sub g}:m{sub b} trends for explosions and earthquakes continue to separate at small magnitudes at regional distances. Although NTS is unique from other test sites in its geologic characteristics, this dataset of explosions and earthquakes is ideal for a number of reasons: (I) continuous recordings from high-quality broadband stations, (2) ground truth information that far exceeds any other area, (3) path and site effects that are virtually common for all events, and (4) wide range in depth, source size, and material properties. Because our goal is phenomenological in scope, we will use these results to guide our interpretations and assess our capability in other areas of monitoring interest.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15013168
- Report Number(s):
- UCRL-JC-138995; TRN: US200802%%1072
- Resource Relation:
- Conference: 22nd Annual Department of Defense/Department of Energy Seismic Research Symposium, New Orleans, LA, Sep 12 - Sep 15, 2000
- Country of Publication:
- United States
- Language:
- English
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