Aretusini S, Meneghini F, Spagnuolo E, Harbord C W, Di Toro G
HPHT Laboratory, INGV, Rome, Italy.
Department of Earth Sciences, University of Pisa, Pisa, Italy.
Nat Commun. 2021 Apr 30;12(1):2481. doi: 10.1038/s41467-021-22805-w.
In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible for the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the Pāpaku thrust (Hikurangi subduction zone, New Zealand). Here, we show that at seismic velocity, shear-induced dilatancy is followed by pressurisation of fluids. The thermal and mechanical pressurisation of fluids, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.
在俯冲带，浅部地壳深度的地震滑动可引发海啸。海啸地震期间的大滑动位移归因于流体饱和且未石化的富含粘土的断层岩石的低同震抗剪强度。然而，由于在限制这些材料方面存在实验挑战，导致断层抗剪强度同震降低的物理过程仍知之甚少。我们使用一种新颖的实验装置，在从新西兰希库朗伊俯冲带帕帕库逆冲断层深海钻探采集的富含粘土的材料中，测量模拟地震滑动过程中的孔隙流体压力。在此，我们表明在地震速度下，剪切引起的扩容之后是流体增压。由断层的低渗透率增强的流体热增压和机械增压，降低了传播地震破裂所需的能量。我们认为，俯冲带浅部出现的流体饱和且富含粘土的沉积物，由于其低渗透率以及在地震滑动速度下剪切时增压的倾向，可促进地震破裂扩展和滑动。
