Locating volcano-seismic signals in the presence of rough topography: wave simulations on Arenal volcano, Costa Rica
Résumé
Quantifying the scattering effects of pronounced volcano topography on the seismic wavefield is an important component in locating and interpreting volcano seismic sources. In this study, we perform seismic wave simulations to quantify the scattering generated by a 3-D digital elevation map and 1-D velocity model of Arenal volcano, Costa Rica. Full waveform synthetic seismograms were generated using a 3-D elastic lattice method including complex topography. Several different simulations were performed where the source location, source type and topographic models were varied. Synthetic seismograms were calculated for 35 seismic arrays each one comprising nine stations. At each array, the slowness vector of wave propagation is estimated from the time delays between the sensors obtained using the cross-spectral method. Results show that the backazimuth estimated for some arrays, in particular those close to the source, deviate from the true source position suggesting strong topographic effects in these regions. The maximum of the probability density function, obtained by crossing the backazimuths of the remaining arrays, coincides exactly with the true source location. We also compare our synthetic seismograms with array results from a physical field study. The true and calculated location misfit depends largely on the topography, but also on the number of antennas, the distance from the source and the spatial resolution of the antennas. The results show that this kind of study could be undertaken prior to the installation of seismic arrays to select the sites that minimize the topographic effects leading to improved source locations.
Domaines
Planète et Univers [physics]
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