Abstract
Seismic data coverage in ocean regions is sparse, and it is highly challenging to build long-term continuous seismic networks in the oceans due to the restrictions related to the shortage of instruments and great costs. The lack of data coverage limits effective seismic imaging of deep mantle structures beneath the oceans, which cover 70% of the Earth’s surface. The newly developed Mobile Earthquake Recorder in Marine Areas by Independent Drivers (MERMAID) can drift with ocean currents at a specified depth while recording seismic signals. The Southern University of Science and Technology (SUSTech) launched 10 MERMAIDs in the South China Sea (SCS) in May 2021 that formed the South China Sea Floating Seismic Network (SCS-FSN). We analyzed the one-year-long records of the SCS-FSN, identifying 372 cataloged earthquakes and acquiring 1,015 high-quality travel time data. By analyzing the records of earthquakes with magnitudes above 7.0 and conducting synthetic waveform calculation, we found that, in addition to the epicentral distance and earthquake magnitude, the earthquake identification ability of the network is also affected by the focal mechanism, sea condition, seafloor relief, and MERMAID working state. Although the recognition rate of the SCS-FSN is only 16% for earthquakes with magnitudes above 5.5 and epicentral distances less than 90°, this network is expected to collect more than 5,000 high-quality travel time data during its five-year battery life. These new data will significantly improve the seismic data coverage, compensating for the lack of long-term continuous seismic network observations in the SCS. Most importantly, with this experiment, we are confident that setting up well-designed floating seismic networks in the world’s three oceans could solve the world-class problem of the lack of effective seismic data coverage beneath ocean regions.
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Acknowledgements
The deployment of the 10 MERMAIDs was supported by the NSFC Open Research Cruise (Cruise No. NORC2021-08), funded by Shiptime Sharing Project of the NSFC. This cruise was conducted onboard R/V “SHIYAN 2” by the South China Sea Institute of Oceanology, Chinese Academy of Sciences. We thank the chief scientist Dr. Xuelin QIU, the captain Dr. Jiazheng ZHANG and all the staff onboard for their support and help. We appreciate the responsible editor and three reviewers for their valuable comments and suggestions. We thank Dr. Zhiqiang LIU from SUSTech for providing the wave height information of the South China Sea and Yizhi WANG for helping with the discussion of the working principle of the hydrophone. The software processing the MERMAID data can be downloaded at https://github.com/joelsimon/omnia/. The figures in this paper were plotted by Generic Mapping Tools (GMT) 6. The work was supported by the National Natural Science Foundation of China (Grant No. 41890814) and the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou).
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Yu, Y., Chen, Y.J., Guo, Z. et al. Long-term seismic network in South China Sea by floating MERMAIDs. Sci. China Earth Sci. 66, 1979–1993 (2023). https://doi.org/10.1007/s11430-022-1100-3
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DOI: https://doi.org/10.1007/s11430-022-1100-3