Preliminary study on microseismic response characteristics of cold seep in Qiongdongnan sea area: A case study of “Haima” cold seep

During the migration, fluid in the cold seep system of the submarine natural gas hydrate area will impact the shallow strata, causing the fluid material in the lower strata to undergo a "solid-liquid-gas" transformation. The energy released could cause fracture collapse and pore rupture, thereby generating a series of vibration events. These microseismic signals can visually and accurately reflect the growth and development status and life cycle of the cold seep system, and reveal the laws of its fluid escape activities. We studied the microseismic data monitored at two different times in 2014 and 2021 near the Haima cold seep area in the Qiongdongnan waters. After preprocessing the data, a large number of microseismic events related to cold seep activities were identified using the STA/LTA (short term average/long term average) method. By analyzing the characteristics of waveform, spectrum, and time distribution of these microseismic signals, the response characteristics of the cold seep microseismic events in the natural gas hydrate area in the Qiongdongnan waters were clarified. Preliminary research 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 signals; the tail of the waveform shows a regular and exponential-like decay, with a duration of 0.3~2 s and a main frequency range of 4~26 Hz. There is no obvious tidal-like time distribution pattern for cold seep microseismic activity, and it mostly shows the characteristics of short-term concentrated distribution, which may be related to the activity and strength of the cold seep vents.