Small Event Yield and Source Characterization using Local P and S-Wave Coda Source Spectra
Abstract
The monitoring mission requires accurate yield estimation for nuclear explosions. Historically, the focus has been on larger yield events (mh > -4.5) using teleseismic body wave magnitudes and applying test-site-specific corrections for yield estimates. The regional coda methodology provides unprecedented stability and avoids test site bias because it is based upon absolute source spectra. Increasingly however, there is interest in monitoring smaller events both for yield and source characterization. Unfortunately, these events may only be recorded with adequate signal-to-noise ratio at local distances from one static. The project goals were to extend the well-established 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. Previous studies show that local coda has a unique property of homogenizing its energy over a volume of the Earth's crust such that path corrections for distances less than -200 km are not necessary or minimal at worst. The recent 2008 Mw 5.8 Wells, Nevada earthquake was well recorded by the U.S. Array and we show that the local-to-near-regional coda is virtually insensitive to the source radiation pattern and directivity effects. Furthermore, we demonstrate the coda wavefield becomes homogenized a few tens of seconds past the expanding direct-wave front. This past year, we have also calibrated a number of paths in Japan and compare those to our previous years' work. We have compared S-wave coda path attenuation curves, envelopes shapes, and peak velocity from a variety of regions to look for similarities and differences that could be correlated to the degree of tectonic activity. This special feature may make it easier to define ana priori set of coda calibration parameters that can be transported to new, but geophysically similar regions.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 2009
- Accession Number
- ADA505416
Entities
People
- Kevin Mayeda