地壳脆塑性转化带非稳态流变与震后松弛变形机制

大陆浅源地震密集分布层称为地震层,该深度处于石英脆塑性转化带,其变形除受温度控制外,地震周期各阶段变形随应变速率和应力发生变化,从间震期的稳态蠕变转化为同震破裂和震后松弛阶段非稳态蠕变。与间震期长期蠕变相关的野外塑性变形和稳态流变实验研究非常多,而与震后松弛相关的地壳深部脆塑性转化和非稳态蠕变研究非常有限,更缺少非稳态流变的本构方程。震后松弛阶段的断层滑动研究和基于GPS观测数据反演地壳形变研究都依赖于非稳态蠕变实验数据及其流变模型。本文介绍了野外断层脆塑性转化带非稳态流变和高温高压非稳态流变实验研究进展,分析震后松弛阶段断层脆塑性转化带的变形特征与变形模式,讨论了非稳态流变与脆塑性转化带强度定量化研究中存在的问题。

Transient creep during crustal brittle-plastic transition and deformation mechanism of postseismic relaxation

The layer of major seismic events in continental crust at the depth of the quartz brittle-plastic transition zone is called seismogenic zone. The crustal deformation of this zone, controlled by temperature and affected by strain rate and stress, plays an important role during seismic cycle. The major deformation mechanism is steady state creep during interseismic deformation, then changing to rupture at coseismic loading and transient creep at postseismic relaxation. However, most of the studies in the past were focused on intersceismic creep-related ductile deformation in natural fault and steady state creep tests under high temperature. There have been very limited studies on transient creep-related postseismic relaxation based on geological survey of brittle-plastic fault transition and experiments under high temperature and pressure. Especially, there is an absence of constitutive equations related to transient creep at postseismic relaxation. Fault slip research and GPS observation-based simulation of crustal deformation during postseismic depend on the transient creep test data and rheological model. In this study, we report our research progress on transient creep in brittle-ductile fault zone and under high temperature/pressure, analyze the deformation mechanism and models and discuss issues in quantitative calculation of fault strength for transient creep in brittle-ductile transition zone.