Abstract Database

LOCATING LONG PERIOD EVENTS AND TREMOR BENEATH GALERAS VOLCANO USING SEISMIC AMPLITUDES – STOCHASTIC APPROACH

MEE09178
TORRES CORREDOR Roberto Armando
Supervisor: Hiroyuki KUMAGAI
Country: Columbia
Abstractfulltext

A source location method using seismic amplitudes is applied to locate long period (LP) events and tremor at Galeras volcano. Galeras in the Colombian Andes is an active andesitic stratovolcano. This method is appropriate to estimate source locations of seismic signals that show emergent onsets such as LP events, or stationary signals for a long time that do not exhibit onset times such as tremor. The method assumes isotropic radiation of S-waves and uses seismic amplitudes corrected for station site effects. Site amplification was estimated at stations of the Galeras network in five different frequency bands (1-6, 3-8, 5-10, 7-12, and 9-14 Hz) using the coda normalization method. The estimated site amplification factors may be consistent with geological features observed at Galeras. For source location determinations, grid searches with respect to the frequency range, quality factor for medium attenuation (Q), and space for each origin time were performed in each event to estimate the minimum normalized residual, which is regard as the source location. The five frequency bands used in the estimations of site amplification factors were used in source location determinations. For LP events, the best-fit locations were found using a frequency band of 9-14 Hz and Q values of around 70. Also, using these parameters, a reasonable source location was estimated for tremor. It has been interpreted that the isotropic S-wave radiation assumption becomes valid in high frequency bands because of the path effect caused by the scattering of seismic waves propagating in structural heterogeneities beneath volcanoes. This study supports this interpretation and demonstrates the applicability of the source location method to LP events and tremor at Galeras volcano.

Citation: Bulletin of IISEE, 45, 7-12.