Using Ocean-Bottom Seismometer (OBS) Data to Analyze Ambient Noise in the Huatung Basin Offshore Eastern Taiwan

Abstract:

We apply recently well-developed and popular method of ambient noise analysis on an OBS array dataset offshore eastern Taiwan. Different to traditional method it doesn’t require recordings of nature earthquakes. We can analyze the continuous seismic waveform data without earthquake signals to obtain the characteristics of surface wave propagation. The OBS array used in this study include six stations installed in the Huatung Basin, operating during September 2012- June 2013. Three of the stations were located at ~1500 km depth and the other three were at ~4500 km depth. First, we analyze its noise correlation function (NCF) and obtain the coherency between stations in time domain. Second, we stack the cross-correlation pairs for all period for about 290 days to enhance the signal coherency. Third, we obtain the phase velocity of the surface waves, which presents ~0.5-1.5km/s in the Huatung Basin. Finally, we separate data pairs every 20 days and stack them to obtain their spectrograms, in order to inspect the seasonal changes of ambient noise. Our results show that the ambient noise is strongest in December and January. Further, we analyze the spectrum of every single station. The dominant energy peak is at 4-5sec, which is generated by second long ocean waves called short period secondary microseism (SPSM). [Chen et al., 2011]