Identification of surface wave higher modes using a methodology based on seismic noise and coda waves
Por:
Rivet, D, Campillo, M, SanchezSesma, F, Shapiro, NM, Singh, K
Publicada:
1 nov 2015
Resumen:
Dispersion analysis of Rayleigh waves is performed to assess the
velocity of complex structures such as sedimentary basins. At short
periods several modes of the Rayleigh waves are often exited. To perform
a reliable inversion of the velocity structure an identification of
these modes is thus required. We propose a novel method to identify the
modes of surface waves. We use the spectral ratio of the ground velocity
for the horizontal components over the vertical component (H/V) measured
on seismic coda. We then compare the observed values with the
theoretical H/V ratio for velocity models deduced from surface wave
dispersion when assuming a particular mode. We first invert the Rayleigh
wave measurements retrieved from ambient noise cross-correlation with
the assumptions that (1) the fundamental mode and (2) the first overtone
are excited. Then we use these different velocity models to predict
theoretical spectral ratios of the ground velocity for the horizontal
components over the vertical component (H/V). These H/V ratios are
computed under the hypothesis of equipartition of a diffuse field in a
layered medium. Finally we discriminate between fundamental and higher
modes by comparing the theoretical H/V ratio with the H/V ratio measured
on seismic coda. In an application, we reconstruct Rayleigh waves from
cross-correlations of ambient seismic noise recorded at seven broad-band
stations in the Valley of Mexico. For paths within the soft quaternary
sediments basin, the maximum energy is observed at velocities higher
than expected for the fundamental mode. We identify that the dominant
mode is the first higher mode, which suggests the importance of higher
modes as the main vectors of energy in such complex structures.
Filiaciones:
Rivet, D:
Univ Nice Sophia Antipolis, CNRS, Geoazur, Cote dAzur Observ, F06560 Sophia Antipolis, France
Campillo, M:
Univ Grenoble 1, Inst Sci Terre, F38041 Grenoble, France
SanchezSesma, F:
Univ Nacl Autonoma Mexico, Inst Ingn, CU, Mexico City 04510, DF, Mexico
Shapiro, NM:
CNRS UMR7154, Inst Phys Globe Paris, Sorbonne Paris Cite, F75238 Paris 5, France
Singh, K:
Univ Nacl Autonoma Mexico, Inst Geofis, Mexico City 04510, DF, Mexico
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