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<p>Accurate assessment of the changing thermal structure of megathrusts at the global scale is difficult because the subduction regime depends on the three-dimensional (3-D) geometry of slabs. Although the slab dip has been studied extensively, the specific implications of subduction geometries have not been well assessed. In this study, we propose an integrated thermal model that can be used to infer and quantify the ways in which the slab morphology influences the thermal state of the incoming plate below Hokkaido. Our model accounts for both the slab topography and subduction obliquity variations along the trench. The results reveal correspondence between the temperature structure, water content distribution, and observations of subduction earthquakes. Moreover, the results suggest that the primary episode of dehydration below Hokkaido occurs between depths of ~ 40 and 100&#xa0;km, with temperatures ranging from 300&#xa0;°C to &gt; 700&#xa0;°C, where the metamorphic transition of basaltic crust from greenschist to amphibolite and ultimately to eclogite facies induces massive water release, yielding the occurrence of most earthquakes. A dehydration belt with a rate exceeding 0.05 wt%/km occurs at the lower limit of the seismic zone. The rate is notably higher near the bending of the trench, where plate bending generates fractures that facilitate seawater penetration and cause serpentinization. The thermal shielding effect originating from the subducting cold oceanic plates results in low surface heat flow (&lt; 80 mW/m<sup>2</sup>) in the forearc region of Hokkaido, whereas magmatic and hydrothermal activities induced by slab dehydration and melting cause significantly elevated heat flow, with localized anomalies &gt; 120 mW/m<sup>2</sup> near volcanic arcs.</p>

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Reassessed changes in the thermal structure below Hokkaido: implications for slab metamorphism and earthquakes

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月23日

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  • Haris Faheem,
  • Ye Zhu,
  • Yingfeng Ji,
  • Jun Yang,
  • Fitriani Fitriani,
  • Shoichi Yoshioka,
  • Nobuaki Suenaga

摘要

Accurate assessment of the changing thermal structure of megathrusts at the global scale is difficult because the subduction regime depends on the three-dimensional (3-D) geometry of slabs. Although the slab dip has been studied extensively, the specific implications of subduction geometries have not been well assessed. In this study, we propose an integrated thermal model that can be used to infer and quantify the ways in which the slab morphology influences the thermal state of the incoming plate below Hokkaido. Our model accounts for both the slab topography and subduction obliquity variations along the trench. The results reveal correspondence between the temperature structure, water content distribution, and observations of subduction earthquakes. Moreover, the results suggest that the primary episode of dehydration below Hokkaido occurs between depths of ~ 40 and 100 km, with temperatures ranging from 300 °C to > 700 °C, where the metamorphic transition of basaltic crust from greenschist to amphibolite and ultimately to eclogite facies induces massive water release, yielding the occurrence of most earthquakes. A dehydration belt with a rate exceeding 0.05 wt%/km occurs at the lower limit of the seismic zone. The rate is notably higher near the bending of the trench, where plate bending generates fractures that facilitate seawater penetration and cause serpentinization. The thermal shielding effect originating from the subducting cold oceanic plates results in low surface heat flow (< 80 mW/m2) in the forearc region of Hokkaido, whereas magmatic and hydrothermal activities induced by slab dehydration and melting cause significantly elevated heat flow, with localized anomalies > 120 mW/m2 near volcanic arcs.