Small-Event Yield and Source Characterization Using Local P and S-Wave Coda Source Spectra
Abstract
The Air Force Technical Applications Center mission requires accurate yield estimation for nuclear explosions. Historically, focus has been on larger yield events using teleseismic body wave magnitudes and applying test site specific corrections for yield estimates. Regional coda methodology provides unprecedented stability and avoids test site bias as it is based upon absolute source spectra. There is interest in monitoring smaller events. However, these events may only be recorded with adequate signal to noise ratio at local distances from one station. Project goals were to extend regional coda methodology to local distances using S and P wave codas in regions of little-to-no calibration data and/or regions of high attenuation and lateral complexity. Studies show local coda has a unique property of homogenizing its energy over a volume of the Earth's crust such that path corrections for distances <200 km are not necessary or minimal. Our plan was to use existing data from a variety of active tectonic settings and source types to assess performance under the assumption of little to no calibration data. We have compared S-wave coda path attenuation curves from a variety of regions to look for correlation to tectonic activity. We can make some preliminary statements. First, central Italy exhibits the strongest attenuation for distances ranging between 20-300 km. Upstate New York, South Africa, and the Korean Peninsula have lowest attenuation; these regions are the most tectonically stable. This special feature may make it easier to define an a priori set of coda-calibration parameters that can be transported to geophysically similar regions. It appears tectonically similar regions have similar a coda path, envelope shape, and peak envelope velocity, which allow us to derive average "local background" models to other regions for testing and evaluation, including cases to mimic uncalibrated, single-station deployment.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2008
- Accession Number
- ADA516269
Entities
People
- Kevin Mayeda