Identification and characteristics analysis of microseismic events in the "Haima" cold seep area

During the process of fluid transport in the cold seep system at the natural gas hydrate zone, the shallow part of the stratum will be impacted by the fluid, and at the same time, there is a “solid-liquid-gas” transformation of the fluid material in the lower stratum, and the release of energy will lead to vibration events such as fissure collapse and pore rupture, which will produce a series of micro-seismic signals related to the cold seep activity. These microseismic signals can visually and accurately reflect the growth and development status and life cycle of the cold seep system and reveal its fluid escape activity pattern. We use the microseismic data recorded by the ocean-bottom seismometers at two different years, 2014 and 2021, near the “Haima” cold seep in the gas hydrate zone of the Qiongdongnan sea area as the research data. After corresponding preprocessing, a large number of microseismic events related to cold seep activities are identified by using the STA/LTA method. The waveform characteristics, spectral characteristics, and time distribution characteristics of these microseismic signals are then analyzed in order to further understand the characteristics of cold seep microseismic events. The results show that the microseismic events generated by the cold seep activity in the “Haima” cold seep area include short-duration events and typical cold seep microseismic event signals. In these microseismic events, the tail of their waveforms shows a regular decay similar to an exponential pattern, with durations ranging from 0.3s to 2s and the peak frequency distribution in the range of 4-26 Hz, and the occurrence of cold seep microseismic events does not have an obvious tidal temporal distribution pattern but mainly exhibits short-term concentrated distribution characteristics.