Geodetically Inferred Locking State of the Cascadia Megathrust Based on a Viscoelastic Earth Model
Geodetically Inferred Locking State of the Cascadia Megathrust Based on a Viscoelastic Earth Model
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基于粘弹性地球模型的卡斯卡迪亚巨型逆冲断层的大地测量推断锁定状态
DOI：
10.1029/2018jb015620
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
S. Dosso
中科院分区：
文献类型：
--
作者：
Shaoyang Li;Kelin Wang;Yanzhao Wang;Yan Jiang;S. Dosso
在粘弹性地球中，由于断层锁定而缓慢建立的应力在整个震间期同时松弛。这种震间应力松弛导致地壳变形远离锁定断层，比使用忽略松弛的弹性模型解释的距离要远得多。在这里，我们开发了一个粘弹性大地测量反演模型来解决卡斯卡迪亚的这个问题。我们根据过去二十年的连续和运动大地测量数据反演了约 500 个水平速度矢量。通过使用两种不同的块运动模型测试校正大地速度来解决上板块地壳块的长期旋转引起的模糊性。断层后滑（即滑移赤字）格林函数是使用具有真实俯冲带结构和巨型逆冲几何形状的麦克斯韦粘弹性有限元模型导出的。首选模型具有狭窄而浅的巨型逆冲锁定区，与早期的热流变推理一致。对于使数据达到相同保真度的弹性模型，巨型推力锁定必须扩展到更大的深度。然而，即使采用粘弹性模型，陆基大地测量数据仍然无法解析远海巨型逆冲断层最浅部分是否存在蠕变（不完全锁定）。陆地数据也不能完全解决锁定状态的沿走向变化。只有获得足够的海底大地测量数据才能解决这些歧义。
In a viscoelastic Earth, stresses slowly built up due to fault locking are relaxed concurrently during the entire interseismic period. This interseismic stress relaxation causes crustal deformation much farther away from the locked fault than can be explained using elastic models that neglect the relaxation. Here we develop a viscoelastic geodetic inversion model to address this problem at Cascadia. We invert ~500 horizontal velocity vectors based on continuous and campaign geodetic measurements over the past two decades. Ambiguities arising from long‐term rotation of upper‐plate crustal blocks are addressed by test‐correcting the geodetic velocities with two different block‐motion models. Fault back slip (i.e., slip deficit) Green's functions are derived using a Maxwell viscoelastic finite element model with realistic subduction zone structure and megathrust geometry. The preferred model features a narrow and shallow megathrust locked zone, consistent with earlier thermorheological reasoning. For an elastic model to fit the data to the same fidelity, megathrust locking has to extend to much greater depths. However, even with the viscoelastic model, the land‐based geodetic data still cannot resolve whether there is some creep (incomplete locking) in the shallowest part of the megathrust far offshore. Neither can the land data fully resolve along‐strike variations of the locking state. These ambiguities can be resolved only when adequate seafloor geodetic data are obtained.
影响因子：
3.9
作者：
Li, Shaoyang;Moreno, Marcos;Oncken, Onno
通讯作者：
Oncken, Onno