近日，中国地震局地质研究所段庆宝及其团队在研究中国红河断裂的中地壳地质特征时，提出了流体环境控制滑动方式的沿走向变化这一新看法。相关论文于2024年2月28日发表在《地质学》杂志上。

本文描述了中国红河断层的摩擦—粘质剪切带，它由两个具有不同地震行为和流体可利用性的部分组成。北段发生中到大地震，中地壳断层滑动局限于含糜棱岩化假玄武质层，动态重结晶石英记录了超过100MPa的流动应力，并加速了粘质蠕变。南段主要为无震区但微地震活跃。断层滑动出现在几个糜棱岩化碎裂岩层中，包括相互连接的黑云母和中间的断裂碎屑，具有普遍的溶解—沉淀蠕变的证据。

微观结构、古测压发和微物理模型表明，在50MPa的粘质蠕变过程中，瞬态地震滑移是对应变速率增加的响应。流体环境中的沿走向变化控制着断层滑动类型和地震行为。干燥且坚固的北段能够形成大地震，而南段较大的流体可用性激活了低驱动应力下的溶解—沉淀蠕变，这限制了摩擦—粘性过渡深度的地震间弹性应变积累。在该模型中，压实驱动的流体增压和膨胀硬化被用来解释南段的无震滑动瞬态。

据了解，大陆中地壳剪切带的滑动样式在确定断层的发震潜力方面起着至关重要的作用，但由于可以直接与地震行为联系起来的地质观测很少，因此人们对它的了解仍然很少。

附：英文原文

Title: Fluid environment controls along-strike variation in slip style: Midcrustal geological signatures from the Red River fault, China

Author: Qingbao Duan, ke Fagereng, Jianye Chen, Thomas Blenkinsop

Issue&Volume: 2024-02-28

Abstract: The slip style of continental midcrustal shear zones plays a crucial role in determining the seismogenic potential of faults, but it remains poorly understood because geological observations that can be directly tied to seismic behavior are scarce. We describe frictional-viscous shear zones in the Red River fault, China, which consists of two segments with distinct seismic behaviors and fluid availabilities. The northern segment hosts moderate to large earthquakes, and midcrustal fault slip is localized into mylonitized pseudotachylyte-bearing layers where dynamically recrystallized quartz records flow stresses exceeding 100 MPa and accelerated viscous creep. The southern segment is dominantly aseismic but active microseimically. Fault slip is accommodated in several mylonitized cataclasite layers, comprising interconnected biotite and intervening fractured clasts, with evidence for pervasive dissolution-precipitation creep. Microstructures, paleopiezometry, and microphysical modeling suggest transient aseismic slip in response to increased strain rates during viscous creep at <50 MPa. We interpret that along-strike variations in fluid environment control fault slip styles and seismic behaviors. The dry and strong northern segment is capable of nucleating large earthquakes, while greater fluid availability in the southern segment activates dissolution-precipitation creep at low driving stresses, which limits interseismic elastic strain accumulation at frictional-viscous transition depths. In this model, compaction-driven fluid pressurization and dilatant hardening are invoked to explain the aseismic slip transients in the southern segment.

DOI: 10.1130/G51865.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G51865.1/635692/Fluid-environment-controls-along-strike-variation