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SEISOU

 

Seismology in the source

People:

Elisa Tinti – elisa.tinti@ingv.it;

Laura Scognamiglio – laura.scognamiglio@ingv.it

Davide Piccinini – davide.piccinini@ingv.it

With SEISOU we aim to compute the following source parameters of the earthquakes nucleating the Alto Tiberina Fault and associated minor segments: Seismic Moment (MO), Moment Magnitude (MW), Source dimension (r), Stress Drop (DS), Apparent Stress; Seismic Energy (ER) and Corner Frequency (FC).

We apply two different techniques:

  1. For normal earthquakes, we assume an omega square model (a), we compute source spectra at each station through a multi-taper technique (b) and we correct for attenuation. Fc is computed using Snoke (c) relation, and Mo is inferred from the spectrum plateau. Therefore for each event FC and MO are estimated computing the median of the inferred distributions.
  2. For clusters of earthquakes, we use the Multi-Window Spectral Ratio technique (MWSR) to avoid the correction of attenuation parameter (d). This technique is based on the fit of the stacked spectral ratios computed from the moving windows through the P and S direct wave.

While the DS is inferred from Elsheby relation (e) and ER is computed from the integral of squared velocity spectra (f).

References:

  1. Brune, J. N., 1970. Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res. 75, 4997–5009.
  2. Thomson, D.J., 1982. Spectrum estimation and harmonic analysis. In: Proceedings of the IEEE, vol. 70, pp. 1055–1096.
  3. Snoke, J.A., 1987. Stable determination of (Brune) stress drops,  Bull. Seismol. Soc. Am., Vol.77, No2, 530-538.
  4. Imanishi, K. & Ellsworth, W.L., 2006. Source scaling relationships of microearthquakes at Parkfield, CA, determined using the SAFOD pilot holeseismic array, Earthquakes: Radiated Energy and the Physics of Faulting, Geophys. Monogr. Ser. Vol. 170, pp. 81–90, eds Abercrombie, R., McGarr, A., Kanamori, H. & Di Toro, G., American Geophysical Union, Washington, DC.
  5. Eshelby, J.D., 1957. The determination of the elastic field of an ellipsoidal inclusion and related problems, Proc. R. Soc.Lond., 241, 376–396.
  6. Singh, S.K., and M. Ordaz, 1994. Seismic energy  release in Mexican subduction zone earthquakes, Bull. Seismol. Soc. Am. , Vol. 84, 1533-1550.