海山俯冲对希库朗伊增生楔构造变形的影响:基于离散元模拟的认识  

Effects of seamount subduction on structural deformation of Hikurangi accretionary wedge: Insights from discrete-element modeling

作　　者：王明 王毛毛 郭仔佚 WANG Ming;WANG Maomao;GUO Ziyi(College of Oceanography,Hohai University,Nanjing 210098,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]河海大学海洋学院,南京210098 [2]北京大学地球与空间科学学院,北京100871

出　　处：《海洋地质与第四纪地质》2023年第1期82-93,共12页Marine Geology & Quaternary Geology

基　　金：国家重点研发计划(重大自然灾害防控与公共安全)“构建三维公共断层模型和四维构造动态演化模型”(2021YFC3000604);国家自然科学基金面上项目“四川盆地南部高应变构造变形与诱发地震的相关性研究”(42172232)。

摘　　要：海山等粗糙海底的俯冲对增生楔的结构、地貌、应力和地震灾害有着重要的影响。希库朗伊(Hikurangi)俯冲带位于新西兰北岛外海,希库朗伊高原向西正以40~47 mm/a的速率俯冲于澳大利亚板块之下。希库朗伊高原内部发育大量形态各异的海山,其俯冲造成希库朗伊北缘经历了严重的构造侵蚀。目前该区域的慢滑移事件有了很好的地震学和测地学约束,但对于希库朗伊北缘的构造侵蚀和构造应力体制如何演化以及对地震活动的影响仍然不清。本文基于离散元方法(DEM)数值模拟,结合地震反射剖面,探讨了海山俯冲对希库朗伊俯冲带北缘增生楔的形态、断裂结构、活动性、应变分配的影响。模拟结果显示海山的俯冲在其顶部形成一条巨型分支断层(mega-splay fault),吸收主要的缩短量并沿海底发生长距离、低角度逆冲推覆。随着俯冲的持续,海山前缘形成一个双重构造剪切带,而随着滑脱层的下移并向前扩展,最终形成前缘逆冲断裂体系。模拟证实海山俯冲提高了弧前增生楔内应力分布的非均质性,海山前缘最大剪切应力显著累积,而海山后缘则表现为一个稳定的应力影区。海山俯冲显著增加了希库朗伊俯冲带板间逆冲断层的几何粗糙度和物质非均质性,对微地震和慢滑移事件的产生具有重要影响。Subduction of rough seafloor such as seamounts has an important influence on structure, geomorphology, stress, and seismic hazard of accretionary wedges. The Hikurangi subduction zone lies on the North Island of New Zealand, and the Hikurangi Plateau is subducting beneath the Australian Plate at a rate of 40 –47 mm/a. Many seamounts of various shapes are distributed in the Hikurangi Plateau, whose subduction caused severe tectonic erosion along the northern Hikurangi Margin. In recent years, slow slip events(SSEs) have been well documented in seismology and geodesy at the Hikurangi northern margin. However, the evolution of tectonic erosion, structural stress regime,and their influences on seismicity remain unclear. By applying the discrete-element numerical simulation in combination with the interpretations of seismic reflection profile, the effects of seamount subduction on wedge geometry, fault structure, activity and strain distribution of the accretionary prism on the northern Hikurangi subduction margin were analyzed. The simulation result show that the subduction of a guyot seamount formed a mega-splay fault, which absorbed the substantial shortening and thrusts along the seafloor with low angle. With the subduction continued, a duplex shear zone was formed at the leading edge of the seamount, while the detachment moved down and extended forward to evolve into a frontal-thrust zone. Our simulations confirm that the seamount subduction enhanced the heterogeneity of the stress distribution within the forearc accretionary wedge, with significant accumulation of maximum shear stress at the leading edge of the seamount,while the rear edge of the seamount behaved as a stable stress shadow zone. The seamount subduction significantly increased the geometric roughness and material heterogeneity along the megathrust in the Hikurangi Margin, which has important implications for the generation of micro-earthquakes and slow slip events.

关 键 词：海山俯冲 巨型分支断层 双重构造 离散元模拟 希库朗伊俯冲带 

分 类 号：P736.1[天文地球—海洋地质]