Inferring crustal viscosity from seismic velocity: Application to the lower crust of Southern California
Inferring crustal viscosity from seismic velocity: Application to the lower crust of Southern California
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DOI：
10.1016/j.epsl.2018.04.055
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发表时间：
2018-07
影响因子：
5.3
通讯作者：
William J. Shinevar;M. Behn;G. Hirth;O. Jagoutz
中科院分区：
文献类型：
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作者：
William J. Shinevar;M. Behn;G. Hirth;O. Jagoutz
通过对地震P波（Vp）和S波（Vs）速度的联合反演，研究了成分对下地壳粘性的作用。我们确定使用地震速度约束粘度的功效，扩展以前的研究表明地震速度和地壳成分之间的强大关系，以及地壳成分和粘度。首先，我们计算平衡矿物组合和地震速度的地壳岩石在相关的压力和温度的全球汇编。其次，我们使用的流变混合模型，结合主要的地壳形成矿物的单相流动规律，计算预测的矿物组合的总粘度。在α-石英区，地壳粘度与Vp和Vs之间存在强相关性。使用地震数据，大地表面应变率，和热流测量从南加州，我们的方法预测，较低的地壳粘度变化区域的四个数量级，和较低的地壳应力变化的三个数量级在25公里的深度。至少有一半的应力变化可以归因于成分，这意味着区域岩性对下地壳地球动力学有显着的影响。最后，我们用我们的方法来预测的脆韧性过渡的深度，并比较这一区域的地震-抗震过渡的变化。地震-地震转换的变化不能用我们从地球物理观测中推断的模型流变学的变化来解释。因此，我们的结论是，织物的发展，结合成分变化（即石英和云母含量），需要解释的区域变化的地震-地震过渡。
We investigate the role of composition on the viscosity of the lower crust through a joint inversion of seismic P-wave (V p) and S-wave (V s) velocities. We determine the efficacy of using seismic velocity to constrain viscosity, extending previous research demonstrating robust relationships between seismic velocity and crustal composition, as well as crustal composition and viscosity. First, we calculate equilibrium mineral assemblages and seismic velocities for a global compilation of crustal rocks at relevant pressures and temperatures. Second, we use a rheological mixing model that incorporates single-phase flow laws for major crust-forming minerals to calculate aggregate viscosity from predicted mineral assemblages. We find a robust correlation between crustal viscosity and V p together with V s in the α-quartz regime. Using seismic data, geodetic surface strain rates, and heat flow measurements from Southern California, our method predicts that lower crustal viscosity varies regionally by four orders of magnitude, and lower crustal stress varies by three orders of magnitude at 25 km depth. At least half of the total variability in stress can be attributed to composition, implying that regional lithology has a significant effect on lower crustal geodynamics. Finally, we use our method to predict the depth of the brittle–ductile transition and compare this to regional variations of the seismic–aseismic transition. The variations in the seismic–aseismic transition are not explained by the variations in our model rheology inferred from the geophysical observations. Thus, we conclude that fabric development, in conjunction with compositional variations (ie, quartz and mica content), is required to explain the regional changes in the seismic–aseismic transition.