Orientation analysis of the spanish broadband national network using rayleigh-wave polarization

• Autores: Juan José Rueda Núñez, Julio Mezcua Rodríguez
• Localización: Seismological Research Letters, ISSN 0895-0695, ISSN-e 1938-2057, Vol. 86, Nº. 3, 2015, págs. 929-940
• Idioma: inglés
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• Resumen

  • The orientation of seismic instruments relative to north is a critical parameter in many seismological applications. Three-dimensional studies of surface-wave dispersion depend on accurate seismic sensor orientation (Ekström et al., 1997). This parameter is also important in the study of off-great-circle propagation of long-period surface waves (Laske, 1995), as well as in estimates of the anisotropic structure of the mantle using SKS splitting observations (Long et al., 2009). Finally, sensor orientation is critical in the comparison of observed and synthetic records in seismic source studies. In a recent study of southern Iberia and the influence of the moment tensor resolvability, Zahradnik and Custodio (2012) found that a 10° sensor misorientation induces data errors that vary between 10% and 40% of the amplitude of the original waveform; for a station with a 30° misorientation, the original waveform will thus have an error between 30% and 90%. These are just a few examples from seismic research showing the great influence that correct orientation exerts on a seismic station's horizontal components.

    Several factors act as sources of misorientation. First, in many seismic networks, such as the Spanish Broadband National Network (SBNN), most of the seismometers are installed in abandoned mines or natural caves that have no direct line of sight to any external point of reference. An overall precision of ±1° has been reached using precise magnetic orientation; however, this is not possible in locations where magnetic material is present. Often, reorientations are not performed during reinstallations, maintenance visits, or seismometer changes. There is no information available or recorded regarding operational routing; in other words, there is no obtainable log of possible relocations of seismometer. Second, the orientation obtained at the entrance to the site...