Tertiary Waves Measured during 2017 Pohang Earthquake Using an Underwater Glider

Abstract

An underwater glider equipped with a hydrophone observed the acoustic sounds of an earthquake that occurred on 15 November 2017 05:29:32 (UTC) in the Pohang area. The underwater glider observed the earthquake sounds after 19 s (05:29:51) at approximately 140 km from the Pohang epicenter. In order to distinguish the earthquake sound from the glider’s operation noise, the noise sources and Sound Pressure Level (SPL) of the underwater glider were analyzed and measured at laboratory tank and sea. The earthquake acoustic signal was distinguished from glider’s self-noises of fin, pumped Conductivity-Temperature-Depth profiler (CTD) and altimeter which exist over 100 Hz. The dominant frequencies of the earthquake acoustic signals due to the earthquake were 10 Hz. Frequencies at which the spectra had dropped 60 dB were 50 Hz. By analysis of time correlation with seismic waves detected by five seismic land stations and the earthquake acoustic signal, it is clearly shown that the seismic waves converted to Tertiary waves and then detected by the underwater glider. The results allow constraining the acoustic sound level of the earthquake and suggest that the glider provides an effective platform for enhancing the earth seismic observation systems and monitoring natural and anthropogenic ocean sounds.

Special Issue on “Mapping and Monitoring of Geohazards”

“…The published papers cover three types of geohazards across eight different countries: earthquake [4][5][6], landslide [7][8][9][10][11][12][13][14], and volcanic hazards [15]. As of 21st May 2020, almost 6 months after the deadline for submissions, the 12 papers have been viewed 6096 times, downloaded 4868 times, and cited 16 times overall.…”

“…The second paper by Lee et al [5] establishes constraints on the acoustic sound level of the 2017 Pohang Earthquake (South Korea) using an underwater glider. This analysis can be critical for a comprehensive analysis of seismic sources offshore to be used in the earthquake disaster risk assessment of coastal zones.…”