Characteristics of the autocorrelation function decay rate of ambient noise
Abstract
To monitor volcanic activities, seismic studies on heterogeneous structures such as cracks and dikes beneath a volcano and their temporal variations would make a huge contribution. The spatio-temporal distribution of the decay rate of a coda wave, Qc, is expected to give important information about the heterogeneous structures, because the coda waves are composed of scattered waves and affected by the change in the medium or the scatters. However, the analyses of Qc require the occurrence of proper earthquakes near the stations, which are generally rare. Instead of the usage of the coda waves, the autocorrelation function of ambient noises may be useful, since the autocorrelation function of the noise at one station gives the signal equivalent to the coda wave whose hypocenter and the station are at an identical location. Wegler & Senns-Schonfelder (2007) showed that the decay rate of the autocorrelation function (Qacf) is in good agreement with Qc for the study region. In this study, we estimated Qacf, investigated its characteristics, and argued the possibility of Qacf to be used for monitoring a volcanic activity. We used vertical components of seismic records from 26 stations in Izu-Oshima volcanic Island, Japan, mainly installed by University of Tokyo. We computed the autocorrelation functions of the data whose durations are one month. The functions were obtained for six periods at every two months in 2008-2009. We regarded the individual autocorrelation function as a coda wave and applied the method by Aki & Chouet (1975) to estimate the decay rate. The ordinary coda decay rates, Qc, in the island, were also estimated from small earthquakes which took place in and around the island. It is found that Qacf represents the coda decay rate of short period surface waves. The spatial distribution of Qacf shows a large variation among the stations, which may delineate the fine near-surface structure of the volcanic island.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.S11B1947M
- Keywords:
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- 7219 SEISMOLOGY / Seismic monitoring and test-ban treaty verification;
- 7280 SEISMOLOGY / Volcano seismology