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Seismic Strain Rate and Flexure at the Hawaiian Islands Constrain the Frictional Coefficient
Geochemistry, Geophysics, Geosystems ( IF 3.275 ) Pub Date : 2021-03-08 , DOI: 10.1029/2020gc009547
A. Bellas, S. J. Zhong

Flexure occurs on intermediate geologic timescales (∼1 Myr) due to volcanic‐island building at the Island of Hawaii, and the deformational response of the lithosphere is simultaneously elastic, plastic, and ductile. At shallow depths and low temperatures, elastic deformation transitions to frictional failure on faults where stresses exceed a threshold value, and this complex rheology controls the rate of deformation manifested by earthquakes. In this study, we estimate the seismic strain rate based on earthquakes recorded between 1960 and 2019 at Hawaii, and the estimated strain rate with 10−18–10−15 s−1 in magnitude exhibits a local minimum or neutral bending plane at 15 km depth within the lithosphere. In comparison, flexure and internal deformation of the lithosphere are modeled in 3D viscoelastic loading models where deformation at shallow depths is accommodated by frictional sliding on faults and limited by the frictional coefficient (μf), and at larger depths by low‐temperature plasticity and high‐temperature creep. Observations of flexure and the seismic strain rate are best‐reproduced by models with μf = 0.3 ± 0.1 and modified laboratory‐derived low‐temperature plasticity. Results also suggest strong lateral variations in the frictional strength of faults beneath Hawaii. Our models predict a radial pattern of compressive stress axes relative to central Hawaii consistent with observations of earthquake pressure (P) axes. We demonstrate that the dip angle of this radial axis is essential to discerning a change in the curvature of flexure, and therefore has implications for constraining lateral variations in lithospheric strength.

中文翻译:

夏威夷群岛的地震应变率和挠曲约束了摩擦系数

由于夏威夷岛上的火山岛建设,挠曲发生在中间的地质时标上(约1 Myr),岩石圈的变形响应同时具有弹性,塑性和延性。在浅层深度和低温下,在应力超过阈值的断层上,弹性变形会转变为摩擦破坏,这种复杂的流变性控制着地震所表现出的变形速率。在本研究中,我们根据1960年至2019年在夏威夷记录的地震估算地震应变率,并估算10 -18 –10 -15 s -1时的应变率。大小在岩石圈内15 km深度处表现出局部最小或中性的弯曲平面。相比较而言,岩石圈的弯曲和内部变形进行建模,其中在浅的深度变形是通过摩擦滑动上的故障容纳并通过摩擦系数(限于3D粘弹性加载模型μ ˚F通过低温塑性),并且在更大的深度和高温蠕变。挠曲和地震应变速率的观测通过用模型最好再现μ ˚F = 0.3±0.1,并改进了实验室衍生的低温可塑性。结果还表明,夏威夷下方断层的摩擦强度存在较大的横向变化。我们的模型预测了相对于夏威夷中部的压应力轴的径向模式,与地震压力(P)轴的观测结果一致。我们证明了该径向轴的倾角对于辨别弯曲曲率的变化至关重要,因此对于约束岩石圈强度的横向变化具有影响。
更新日期:2021-04-08
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