Geoacoustic Investigation and in-situ P-wave Speeds of Muddy and Sandy Top Strata in Jinhae Bay, Southern Korea

Woo Hun Ryang, Jeonbuk National University, Jeonju, South Korea, Gwang-Soo Lee, Korea Institute of Geoscience and Mineral Resources, Daejeon, South Korea and Jooyoung Hahn, Agency for Defense Development, South Korea
In-situ P-wave speeds were estimated using the Hamilton geoacoustic modeling at fine-grained and coarse-grained top strata in Jinhae Bay of southern coast of Korea. The P-wave speeds were compared with the results of bottom reflection measurements, fulfilled by underwater acoustic experiments. Measurements of bottom-interacting signals over a frequency range of 4-12 kHz were made at two sites in shallow water of Jinhae Bay, ranging from 50 to 65 m in water depth. The study area lies on the continental shelf of the rias coast, which consists of inner shelf environment in bay area and outer shelf environment in offshore area. Surficial sediments in the inner shelf area were dominated by mud of 7.5~8.5 ϕ, originating from the adjacent Nakdong River during the Holocene, and the sandy sediments in the outer shelf formed in coastal environments during transgression of the last glacial period. We reconstructed bottom and geoacoustic models in Jinhae bay, based on the seismic data acquired by chirp sonar, sub-bottom profiler, sparker, and air-gun profiles as well as core samples including 7 short piston cores (1.0 to 5.6 m in depth below the seafloor) and one long core (31.6 m in depth below the seafloor). The in-situ P-wave speeds of geoacoustic modeling represented 1462-1467 m/s in muddy site and 1567-1573 m/s in sandy site, whereas those of bottom reflection measurements showed 1445.5±2 m/s in muddy site and 1569.7±1 m/s in sandy site.

Keywords: shelf environment, geoacoustic modeling, in-situ P-wave speeds, Jinhae Bay

Acknowledgements: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2019R1F1A1057715) and by the Agency of Defense Development (ADD) grant (UD170014DD)