Gas Emission Characteristics and Tectonic Implications in the Southernmost Okinawa Trough From Split‐Beam Echo Sounder Observations

Abstract

AbstractTraditionally, single‐beam echo sounder (SBES) data are used to determine the position of emission structures in the form of a two‐dimensional profile, which may not be straightforward enough to correlate the data of adjacent profiles and determine the exact discharge area. In this study, we develop semiautomatic software to remove noise and select possible flare signals to enhance the speed and precision of the data processing. The program also allows for the transformation of the data into a three‐dimensional point cloud distribution by computing the receiving angle of the data. By applying this method to investigate the distribution and mechanism of gas emission structures in the South Okinawa Trough (SOT), we determine four high flux areas and 22 isolated plumes with roots. Widespread gas flares usually occur in areas with large‐scale volcanic activity or gas‐enriched structures. Isolated gas plumes could be found for a single knoll outcrop and normal faulting structures. The energy of the flares around the knoll area is generally stronger than that observed along the normal faults. Compared with other geophysical data, we find that the widespread distribution of gas flares generally implies a larger hydrothermal potential, which may not be revealed by single‐profile acoustic image observations. We also find that the direction of flares is strongly influenced by tides, and the height of the flare represents the thermocline as a strong boundary for bubbles composited by carbon dioxide.