Papers Published

1. Blakeslee, S.N. and Malin, P.E., A comparison of earthquake coda waves at surface versus subsurface seismometers, J. Geophys. Res. (USA), vol. 95 no. B1 (1990), pp. 309 - 26 .
   (last updated on 2007/04/09)

   Abstract:
   The coda waves of 21 Parkfield earthquakes were recorded simultaneously at the surface and at a depth of 198 m. These codas are characterised by computing the time dependence of the integral of squared particle velocity, their frequency content, time-frequency coda decay planes, the frequency dependence of root mean square ellipticity, and the difference in their normalized decay rates. These five measures reveal significant differences in the early portion of the uphole versus downhole codas. Average apparent coda Q for the 21 events is Q_a(f,τ)=39(f/f₀)^0.43(τ/τ₀)^0.37, with the reference frequency and time defined at 1 Hz and 1 s, respectively. The spectral ratio between the uphole signal and the downhole signal varies with time through the coda. The early portion of the uphole coda experiences a pulse of low-frequency energy not seen in the downhole coda. This observation is explained by a model of the coda that includes body wave to surface wave scattering near the site

   Keywords:
   earthquakes;Q-factor;scattering;seismic waves;seismology;