Evidence that scattering due to nonlinear elasticity contributes to coda waves.
Abstract
Different factors might affect the propagation of seismic waves producing scattering, including heterogeneities and nonlinear elasticity. A key difference between these two factors is the dependence of the strength of the scattered waves on the strength of the incident wave, being linear for the former and nonlinear for the latter. A detailed study of these dependences using TIPTEQ data, where more than hundred explosions were recorded on 180 three-compomnent stations, most of them in the distance range of approximately 0-18 km (and a few far-offset explosions up to 100 km distance) shows that this dependence is nonlinear. Data were analysed in the following way: (i) the envelope of a bandpass filter between 10 and 40 Hz was obtained for a large number of stations from different ranges and charges of shots, (ii) for these distances we modeled the envelope considering the nonlinear elasticity. The shapes of the theoretical and observed envelopes were in general very similar, and a scale factor for each case was obtained considering the best fit of its complete envelope, (iii) since this scale factor depends mainly on the size of the explosion, we computed the ratio (R) of the scale factor (A) for different size explosions at fixed distances, for distances varying between 0 and 50 km. (iv) we computed the power (p) of the dependence of the ratio (R) on the ratio of charges. (R=(A1/ A2)=(/charge1/charge2/)p). We observe in general that p>1 and for distances between 14 and 18 km, and charges of 75 and 150 kg, the value of p=1.8 ± 0.4. This shows clearly that nonlinear elasticity is an important factor contributing to seismic wave scattering.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.S41B1843C
- Keywords:
-
- 7260 Theory;
- 7299 General or miscellaneous