Abstract
Seismicity in ocean ridge-transform systems reveals fundamental processes of mid-ocean ridges, while comparisons of seismicity in different oceans remain rare due to a lack of detection of small events. From 1996 to 2003, the Pacific Marine Environmental Laboratory of the National Oceanic and Atmospheric Administration (NOAA/PMEL) deployed several hydrophones in the eastern Pacific Ocean and the northern Atlantic Ocean. These hydrophones recorded earthquakes with small magnitudes, providing us with opportunities to study the seismic characteristics of ridge-transform systems at different spreading rates and make further comparisons of their differences. This study comparatively analyzed hydroacoustic and teleseismic data recorded on the fast-spreading East Pacific Rise (EPR, 10°S to 12°N), intermediate-spreading Galapagos Ridge (103° W to 80° W), and slow-spreading Mid-Atlantic Ridge (MAR, 15°N to 37°N). We present a systematic study of the spatial and temporal distribution of events, aftershock seismicity, and possible triggering mechanisms of aftershock sequences. Our analysis yields the following conclusions. (1) From the hydroacoustic data, the EPR transform faults had the highest average seismicity rate among the three regions. (2) Along-ridge event distributions show that a high number of earthquakes were concentrated on the EPR, while they became dispersed on the GR and fewer and more scattered on the MAR, reflecting that the different tectonic origins were closely correlated with the spreading rate. (3) Analysis from mainshock-aftershock sequences shows no significant differences in the aftershock decay rate among the three regions. (4) Multiple types of aftershock triggering models were inferred from Coulomb stress changes: strike-slip mainshocks triggered strike-slip aftershocks and normal faulting aftershocks, and normal faulting mainshocks triggered normal faulting aftershocks. Although these results are case studies, they may be applicable to other ocean ridge-transform systems in future investigations. Our results provide important new insights into the seismicity of global ocean ridge-transform systems.
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Acknowledgements
We are grateful to Zhiyuan Zhou and Fan Zhang for their technical support. We benefited from fruitful discussions and valuable comments from Yangfan Deng and members of the Deep-ocean Geodynamics Group at Tongji University and the South China Sea Institute of Oceanology, Chinese Academy of Sciences.
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Foundation item: The Fund of the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) under contract No. GML2019ZD0205; the National Natural Science Foundation of China under contract Nos 42006055, 41704049, 41890813, 41976066, and 41976064; The Fund of the State Key Laboratory of Marine Geology, Tongji University under contract No. MGK202011; the Scholarship of China Scholarship Council; the Program of Chinese Academy of Sciences under contract Nos Y4SL021001, QYZDY-SSW-DQC005, 131551KYSB20200021, 133244KYSB20180029, and ISEE2021PY03; the International Conference Communication Fund for Graduate Students, Tongji University.
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Zheng, T., Lin, J. & Zhong, Q. Spreading-rate dependence of hydroacoustic and teleseismic seismicity of ridge-transform systems: East Pacific Rise, Galapagos Ridge, and Mid-Atlantic Ridge. Acta Oceanol. Sin. 41, 124–135 (2022). https://doi.org/10.1007/s13131-021-1936-6
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DOI: https://doi.org/10.1007/s13131-021-1936-6