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Conferencia de sismología: «Coda-derived Source Scaling and Ground Motion Validation: Is it Necessary to Have a Break in Self-Similarity?»

  • Fecha: miércoles 4 de julio de 2012
  • Lugar: Salón de actos del Instituto Andaluz de Geofísica (en el Campus de Cartuja, frente a la Facultad de Filosofía)
  • Horario: 11:30 h.
  • Descripción:
    Conferencia impartida por el Dr. Kevin Mayeda, sismólogo del Berkeley Seismological Laboratory (University of California, EEUU).
    Charla sobre un método que ha desarrollado para el escalado del movimiento del suelo a partir de ondas coda. La charla está inicialmente enfocada a los alumnos del master, aunque está abierta a todo aquel que esté interesado.
    • RESUMEN: The ability to predict the high frequency part of strong ground motions is largely dependent upon the accurate, a priori knowledge of the earthquake stress parameter (e.g., stress drop scaling). This has direct application to Ground Motion Prediction Equations which currently do not use a standard model for the stress drop scaling. However, the behavior of earthquake source scaling has been the topic of significant debate in the earthquake source community mainly because traditional methods require substantial path, site, and source radiation pattern corrections that ultimately yield large variances for corner-frequency estimates and subsequently the stress drop estimates. Therefore, determining whether or not a magnitude dependence of stress drop exists is often times obscured by large data variance. Alternatively, the coda ratio method by Mayeda et al. [2007] is a well vetted technique that has been widely used in the explosion monitoring community for accurate source spectral estimation using sparse station deployments and for use in magnitude, discrimination, and explosion yield estimation, with variances that are typically 3-to-4 times smaller than direct wave methods. The method has been applied to numerous earthquake sequences in a variety of geophysical regions and in all regions we find a change in scaling near Mw 5.5 though absolute levels vary. The coda ratio methodology is similar in every respect to the traditional direct wave spectral ratio methods which takes advantage of co-located earthquakes to remove common path and site effects, the so-called Green’s function events. The significant difference however comes from the fact that the coda envelopes are very stable and not sensitive to either the source radiation pattern or source directivity and represent a convolution over the entire source process. We show recent validation examples taken from the Mw 5.9 Wells, Nevada and Mw 6.7 Niigata, Japan earthquake sequences where we compare 5% damped pseudoacceleration (PSA) ratios with self-similar and non-self similar source scaling. Finally, we compare with recent state-of-the-art laboratory friction experiments that show significant slip-weakening when slip exceeds a few tens of centimeters (which roughly corresponds to an Mw 5.5), but varies greatly with the rock type.
  • Organiza: Master en Geofísica y Meteorología (GEOMET), en colaboración con el Instituto Andaluz de Geofísica
  • Más información: Javier Almendros
    Universidad de Granada
    Tel 958 249552
    vikingo@ugr.es

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