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<p>Soil gas radon (<sup>222</sup>Rn) exhalation is a key indicator of both fault activity and deep dynamic processes. In this study, we conducted the first comprehensive survey of soil gas <sup>222</sup>Rn exhalation rates across the Miaodao Archipelago (MA) to evaluate the fault activity and its connection to deep-seated tectonic forces, specifically its relationship to Pacific Plate subduction. In September 2023, radon exhalation rates were measured at 185 sampling sites. The results reveal a local background level of 10,943&#xa0;Bq·m<sup>–3</sup>, with several anomalies reaching up to 59,900&#xa0;Bq·m<sup>–3</sup>, such as in the Moshizui Village–Laofeng Reef area on Tuoji Island, indicating significant radon enrichment. In contrast, a low radon value of 1,010&#xa0;Bq·m<sup>–3</sup> is detected near the crater on Daheishan Island, whereas a high exhalation rate of 20,000&#xa0;Bq·m<sup>–3</sup> is recorded in an adjacent basin. By mapping the areas above anomaly thresholds, we delineated fault systems and zones of elevated radon release. The spatial analysis of soil gas <sup>222</sup>Rn exhalation rates shows that the MA is characterized not only by NE–striking faults linked to the Tancheng–Lujiang Fault Zone (TLFZ), but also by NW- and nearly EW-striking faults associated with the Zhangjiakou–Penglai Fault Zone (ZPFZ). Offshore seismicity clusters along the NW-striking branches of the ZPFZ. Notably, the average soil <sup>222</sup>Rn concentrations across the archipelago exceed those reported for several active volcanic systems worldwide, despite its dormant state. Elevated radon emissions, together with frequent seismic activity, suggest the presence of a submarine tectonic degassing conduit regulated by these fault zones—structures influenced by the ongoing Pacific Plate subduction. These findings demonstrate that soil gas <sup>222</sup>Rn surveying is an effective method for fault characterization in the MA. This approach can also be applied to other dormant volcanic regions, where anomalous radon degassing along active faults may signal seismic hazards linked to crustal fracturing driven by deep plate tectonic processes.</p> Graphical abstract <p></p>

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Quantifying fault-controlled radon degassing induced by Pacific Plate subduction in the Miaodao Archipelago, North China

  • 期刊论文

  • 发表日期：

    2026年3月10日

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  • Shujuan Su,
  • Ying Li,
  • Chang Lu,
  • Yanming Yang,
  • Zhaofei Liu,
  • Fengxia Sun,
  • Jun Liu,
  • Qinglin Wang,
  • Zhigang Liu,
  • Hao Sun,
  • Yaowen Zhang,
  • Chunhong Zou,
  • Min Dong,
  • Zhen Jia

摘要

Soil gas radon (222Rn) exhalation is a key indicator of both fault activity and deep dynamic processes. In this study, we conducted the first comprehensive survey of soil gas 222Rn exhalation rates across the Miaodao Archipelago (MA) to evaluate the fault activity and its connection to deep-seated tectonic forces, specifically its relationship to Pacific Plate subduction. In September 2023, radon exhalation rates were measured at 185 sampling sites. The results reveal a local background level of 10,943 Bq·m–3, with several anomalies reaching up to 59,900 Bq·m–3, such as in the Moshizui Village–Laofeng Reef area on Tuoji Island, indicating significant radon enrichment. In contrast, a low radon value of 1,010 Bq·m–3 is detected near the crater on Daheishan Island, whereas a high exhalation rate of 20,000 Bq·m–3 is recorded in an adjacent basin. By mapping the areas above anomaly thresholds, we delineated fault systems and zones of elevated radon release. The spatial analysis of soil gas 222Rn exhalation rates shows that the MA is characterized not only by NE–striking faults linked to the Tancheng–Lujiang Fault Zone (TLFZ), but also by NW- and nearly EW-striking faults associated with the Zhangjiakou–Penglai Fault Zone (ZPFZ). Offshore seismicity clusters along the NW-striking branches of the ZPFZ. Notably, the average soil 222Rn concentrations across the archipelago exceed those reported for several active volcanic systems worldwide, despite its dormant state. Elevated radon emissions, together with frequent seismic activity, suggest the presence of a submarine tectonic degassing conduit regulated by these fault zones—structures influenced by the ongoing Pacific Plate subduction. These findings demonstrate that soil gas 222Rn surveying is an effective method for fault characterization in the MA. This approach can also be applied to other dormant volcanic regions, where anomalous radon degassing along active faults may signal seismic hazards linked to crustal fracturing driven by deep plate tectonic processes.

Graphical abstract