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The Fingerprints of Flexure in Slab Seismicity
Tectonics ( IF 4.2 ) Pub Date : 2020-08-08 , DOI: 10.1029/2019tc005894
D. Sandiford 1, 2, 3 , L. M. Moresi 2, 4 , M. Sandiford 2 , R. Farrington 2 , T. Yang 5
Affiliation  

Earthquake moment tensors in eastern Pacific (ePac) slabs typically show downdip tensional (DT) axes, whereas in the western Pacific (wPac), they typically show downdip compressional (DC) axes or have mixed orientations indicative of unbending. Prevailing conceptual models emphasize uniform stress/deformation modes, that is, bulk slab stretching or shortening, as the dominant control on intermediate depth seismic expression. In contrast, we propose that a diversity of seismic expression, including DT‐ and DC‐dominated regions, is consistent with expectations of flexural strain accumulation, based on systemic differences in slab geometry. Our analysis reveals two largely unrecognized features of ePac intraslab seismicity. First, earthquake clusters consistent with slab unbending are present in ePac slabs, albeit at much shallower depths than typical of wPac slabs. Second, intermediate depth ePac DT seismicity is strongly localized to the upper half of zones undergoing curvature increase, such as flat slab segments. Our study highlights how the seismic expression of slab flexure is impacted by the relative contribution of brittle and ductile deformation. The strongly asymmetric temperature structure that is preserved in sinking slabs means that seismicity disproportionately records the deformation regime in the colder part of the slab, above the neutral plane of bending. The expression of in‐plane stress may be discernible in terms of a systematic modifying effect on the seismic expression of flexure.

中文翻译:

平板地震的挠曲指纹

东太平洋(ePac)平板的地震矩张量通常显示下倾拉力(DT)轴,而在西太平洋(wPac)中,它们通常显示下倾压力(DC)轴或混合方向,表明未弯曲。现有的概念模型强调均匀的应力/变形模式,即大块平板的拉伸或缩短,是对中深度地震表达的主要控制。相反,我们认为,基于平板几何形状的系统差异,包括DT和DC为主的区域在内的多种地震表达方式与挠曲应变累积的期望是一致的。我们的分析揭示了ePac平板内地震活动性的两个很大程度上无法识别的特征。首先,ePac平板中存在与平板弯曲一致的地震簇,尽管比wPac平板的深度要浅得多。其次,中等深度的ePac DT地震活动强烈地局限在经历曲率增加的区域(例如平板部分)的上半部分。我们的研究强调了板挠性的地震表达如何受到脆性和延性变形的相对影响。保存在下沉平板中的强烈非对称温度结构意味着地震活动不成比例地记录了平板中部弯曲平面上方较冷部分的变形状态。平面应力的表达可以通过对挠性地震表达的系统修正作用来辨别。例如平板段。我们的研究强调了板挠性的地震表达如何受到脆性和延性变形的相对影响。保存在下沉平板中的强烈非对称温度结构意味着地震活动不成比例地记录了平板中部弯曲平面上方较冷部分的变形状态。平面应力的表达可以通过对挠性地震表达的系统修正作用来辨别。例如平板段。我们的研究强调了板挠性的地震表达如何受到脆性和延性变形的相对影响。保存在下沉平板中的强烈非对称温度结构意味着地震活动不成比例地记录了平板中部弯曲平面上方较冷部分的变形状态。平面应力的表达可以通过对挠性地震表达的系统修正作用来辨别。保存在下沉平板中的强烈非对称温度结构意味着地震活动不成比例地记录了平板中部弯曲平面上方较冷部分的变形状态。平面应力的表达可以通过对挠性地震表达的系统修正作用来辨别。保存在下沉平板中的强烈非对称温度结构意味着地震活动不成比例地记录了平板中部弯曲平面上方较冷部分的变形状态。平面应力的表达可以通过对挠性地震表达的系统修正作用来辨别。
更新日期:2020-08-08
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