Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA.
United States Geological Survey, Geology, Minerals, Energy and Geophysics Science Center, Portland, OR, USA.
Nat Commun. 2023 Apr 24;14(1):2352. doi: 10.1038/s41467-023-37063-1.
Despite a lack of modern large earthquakes on shallowly dipping normal faults, Holocene M> 7 low-angle normal fault (LANF; dip<30°) ruptures are preserved paleoseismically and inferred from historical earthquake and tsunami accounts. Even in well-recorded megathrust earthquakes, the effects of non-linear off-fault plasticity and dynamically reactivated splay faults on shallow deformation and surface displacements, and thus hazard, remain elusive. We develop data-constrained 3D dynamic rupture models of the active Mai'iu LANF that highlight how multiple dynamic shallow deformation mechanisms compete during large LANF earthquakes. We show that shallowly-dipping synthetic splays host more coseismic slip and limit shallow LANF rupture more than steeper antithetic splays. Inelastic hanging-wall yielding localizes into subplanar shear bands indicative of newly initiated splay faults, most prominently above LANFs with thick sedimentary basins. Dynamic splay faulting and sediment failure limit shallow LANF rupture, modulating coseismic subsidence patterns, near-shore slip velocities, and the seismic and tsunami hazards posed by LANF earthquakes.
尽管浅层缓倾正断层上很少发生现代大型地震，但全新世 M> 7 级浅层低角度正断层（LANF；倾角<30°）的古地震记录和历史地震及海啸记录都表明其发生过破裂。即使在记录良好的巨型逆冲地震中，断层外非线性塑性和动态复活的分支断层对浅层变形和地表位移的影响，以及由此产生的灾害，仍然难以捉摸。我们开发了活动 Mai'iu LANF 的具有数据约束的三维动力破裂模型，突出了在大型 LANF 地震中多种动态浅层变形机制如何竞争。我们表明，浅层合成分支比陡峭的对偶分支承载更多的同震滑移，限制浅层 LANF 破裂的程度更大。不连续的上盘屈服集中在亚平面剪切带中，指示新启动的分支断层，在具有厚沉积盆地的 LANF 上方最为明显。动力分支断层作用和沉积物失稳限制了浅层 LANF 破裂，调节了同震沉降模式、近岸滑移速度，以及 LANF 地震引起的地震和海啸灾害。
