Microseismic signature of the 2016-2018 cyclones in La Réunion Island.
Abstract
Ocean wave activity generates seismic waves that propagate through the solid earth and are known as microseismic noise. This noise develops in both the so-called primary (PM, from 10 to 20 s period), and secondary (SM, from 3 to 10 s of period) microseismic bands. Here, we analyze the microseismic noise generated by the swell activity during the 2016-2017 and the 2017-2018 cyclonic seasons (December-March) in La Réunion Island (South-West Indian Ocean). We use data from 34 broadband permanent (OVPF (PF) and GEOSCOPE (G) networks) and temporary (Rivièrede Pluies (ZF) network) stations recording in La Réunion Island. To quantify the microseismic noise in each of the PM and SM bands, we compute the RMS of the signal amplitude, the power spectral density (PSD) and measure the signal polarization. The amplitude of the microseismic noise is also correlated with the ocean wave height, as provided by the NOAA WaveWatch III (WWIII) model. The PSD analysis shows that the microseismic noise levels in both the PM and SM bands intensified during the cyclones. In the frequency range from 0.05 Hz to 0.333 Hz, the number of polarized signals increases during the cyclone and remains high at distance <1000 km, which confirms that the microseisms level intensified during the cyclone. In the PM band, our results suggest that the amplitudes of the microseismic noise depend both on the distance and the intensity of cyclones. We observe a clear correlation between the swell height as provided by the WWIII model in the neighborhood of La Réunion Island and the microseismic noise amplitude, indicating that the recorded PM originates in coastal regions and thus confirming that the seismic noise amplitude may be used as a proxy of the swell amplitude. From a distance of 1000 km, the seismic stations start to record the SM. Following the arrival of the SM and depending on the distance, cyclone-station, the swell hits the coast of the Island and generates the PM signal. This demonstrates that SM can be used to monitor the cyclone activity but may also provide a precursory information on swell arrival time and amplitude.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S51D0354R
- Keywords:
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- 9805 Instruments useful in three or more fields;
- GENERAL OR MISCELLANEOUSDE: 9820 Techniques applicable in three or more fields;
- GENERAL OR MISCELLANEOUSDE: 1895 Instruments and techniques: monitoring;
- HYDROLOGYDE: 4315 Monitoring;
- forecasting;
- prediction;
- NATURAL HAZARDS