Case study on the detection and quantification of the gas flares on the southeastern continental shelf of the East Sea, Korea

Since most of the shallow gas is composed of methane, studies on its availability as a resource and global warming are being conducted. A gas flare is called a phenomenon in which shallow gas escapes from the sub-bottom into the seawater. Gas flares cause seafloor deformation and can trigger large-scale geohazards such as landslides and tsunamis. We discovered the gas flares in 2021 and 2022 by conducting seismic and acoustic surveys using R/V TamaheⅡ seismic vessel at the southeastern continental shelf of the East Sea in Korea. The gas flares were detected on the water column data obtained by an EK60 of 38 kHz frequency and a multi-beam echo sounder of 20 – 40 kHz frequency bands (Kongsberg EM2040). We observed the deformation of the seafloor and sub-bottom using a Chirp sub-bottom profiler (SBP) of 2 – 7 kHz frequency bands (FalMouth HMS-622 CHIRPceiver). The water depth of the survey area ranges from 130 to 140 m. Four gas flares are distributed within approximately 3.5 km in a northwest-southeast direction. The height of the gas flare is about a maximum of 100 m from the seafloor. The seafloor where the gas escaped was observed to deform into dome shapes and pockmark. Additionally, we performed the seismic survey using a 60 in3 mini GI gun and a 48-channel streamer cable with a 12.5 m group interval to detect the source layer of shallow gas and the migration pathways. We tried using VBALab software to quantify the gas flow rate on the acoustic data of EK60.