海山俯冲过程与俯冲带强震触发的数值模拟

Subducting Seamount as high bathymetric relief is a common tectonic process in subduction zone, which can change the coupling relationship between subduction plate and overriding plate proved by a great deal of large earthquake records along the globe subduction zones.Contradicting a widely held expectation that subducting seamounts increase the degree of coupling across the subduction interface, subducting seamounts couple two plates weakly. Thus another important problem is proposed, that is, when a seamount subducts, does it genetrate or stop large earthquake? In order to solve this problem, we will study the process of subducting seamounts in different conditions based on I2/3ELVIS numrical Simulation model of Finete Difference Method,and the simulation results will be compared with Geophysical data, Geochemistry data and the fine tectonic feature of accretionary wedge at the different subduction zone. the keys to the study are as follows: (1) To construct geological modeling of the subducting seamounts under various condtions; (2)To define the coupling relationship between the subducting seamounts and the overriding plate; (3)To ascertain the interaction between the subduction interface of subducting seamounts and non-subducting seamounts. Based on these, this project will discuss that can the subducting seamounts trigger large earthquakes at the subduction zone?

海山作为海底高地形向陆缘的俯冲是一种常见的构造过程，该过程能够改变俯冲板块和上覆板块间的耦合关系，这从已有的地震记录可以证实。但对于其耦合方式目前存在着激烈的争论，争论的焦点在于海山俯冲界面到底处于闭锁的强耦合状态，还是蠕变的弱耦合状态。由此引出了另一个关键科学问题，即，海山的俯冲能否触发俯冲带的强震。为了解决这一问题，本项目将以不同俯冲条件下海山俯冲过程作为重点研究对象，采用I2/3ELVIS有限差分数值模型，并结合前人已有的地球物理数据、地球化学数据以及地质调查数据等，侧重以下三方面研究：1)建立俯冲带海山俯冲过程多种条件的地质模型；2)确定俯冲海山与上覆陆壳间的耦合方式；3) 厘定海山俯冲接触界面与周缘非海山俯冲接触界面间的相互作用关系。最后，在以上三点研究基础之上探讨在不同地质条件下海山俯冲过程是否会增加或者降低俯冲带强震发生的可能。

海山作为海底的高地形广泛分布于全球洋壳之上，并伴随洋壳和陆壳间的汇聚，不断向陆壳下俯冲。与陆地断裂带地震一样，海山在俯冲过程中同样能够改变俯冲板块和上覆板块间一定范围内的接触关系，从而影响海山俯冲区及周缘强震的孕育及发生规律。为了研究海山俯冲对地震的控制性作用，本课题基于Crustal 2.0和层析成像数据，以西太平洋俯冲带为例构建了精细的结构非线性和材料非线性的三维数值模型，并得到一下研究结果:(1) 日本俯冲带的历史地震和应力集中区主要位于俯冲带俯冲界面的强耦合区，而强耦合区的发育位置受控于俯冲的海山、洋脊以及其它海底高地形；(2)吕宋俯冲带与日本俯冲带相比，具有相对较少的历史地震，而控制该地震分布样式的主要影响因素是俯冲接触面积的减小和上覆板块性质的转变(由日本岛的陆壳转换为菲律宾板块的洋壳；(3)马里亚纳俯冲带显示了复杂的地震类型，其中逆冲型地震受控于太平洋板块的俯冲过程，正断型地震受控于太平洋板块的俯冲后撤过程，走滑型地震受控于太平洋板块大角度的斜向俯冲过程。本课题研究成果揭示了西太平洋三个次级俯冲带复杂的地震和应力场的分布规律，并认为该规律不但受控于俯冲界面复杂的三维几何学结构特征，还与海山的俯冲过程和俯冲板块的俯冲角度密切相关。