Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones
Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones
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DOI：
10.5194/se-3-355-2012
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发表时间：
2012-11
期刊：
影响因子：
3.4
通讯作者：
P. V. Keken;S. Kita;J. Nakajima
中科院分区：
文献类型：
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作者：
P. V. Keken;S. Kita;J. Nakajima
抽象的。俯冲带中深度（>40公里）地震活动的原因还不清楚。建议的机制，其中包括脱水脆化，剪切不稳定性和流体的存在一般的可行性，在很大程度上取决于当地的条件，包括压力，温度和成分。日本北方（东北和北海道）下方仪器齐全、研究充分的俯冲带为研究中深度地震活动发生的条件提供了一个极好的试验场。这项研究结合了新的有限元模型，预测动力学和热结构的日本俯冲系统与高精度震源数据库。地震活动的上平面主要包含在俯冲板片的地壳部分中，并且在深度>80 km的地壳内变薄和加深。在大部分地区，地震活动的消失与预测的蓝片岩到含水榴辉岩的相变相重叠，后者在地壳中形成了一个主要的脱水锋。在从北方日本到北海道西部以下的千岛岛弧的过渡中，热预测的蓝脊边界和地震活动消失之间的相关性被打破。调整后的模型，考虑到在这个地区的地震成像修改上地幔结构未能充分恢复的相关性，是东北和东部北海道以下。我们的结论是，以下的热结构西部北海道显着影响的时间依赖性，3-D动态的板。这项研究总体上支持流体在中深地震活动中的作用。
Abstract. The cause of intermediate-depth (>40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The well-instrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths >80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by time-dependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity.