Interseismic Coupling and Slow Slip Events on the Cascadia Megathrust
Interseismic Coupling and Slow Slip Events on the Cascadia Megathrust
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DOI：
10.1007/s00024-018-1991-x
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发表时间：
2018-09
影响因子：
2
通讯作者：
S. Michel;A. Gualandi;J. Avouac
中科院分区：
文献类型：
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作者：
S. Michel;A. Gualandi;J. Avouac
在这项研究中，我们利用352个连续GPS站点的位置时间序列，模拟了2007年7月至2017年6月间卡斯卡迪亚俯冲带的大地应变累积。首先，我们利用长期线性运动来确定沿大逆冲构造的震间锁止。我们确定了两种端元模型，假设巨型逆冲构造要么是先验锁住的，要么是爬行的，这两种模型在数据约束较差的海沟上存在本质上的差异。在任何一种情况下，都需要对海岸线的大逆冲上倾进行重大锁定。假设先验锁定，锁定部分的下倾极限位于海岸向上倾斜约20-80公里处，但对于先验爬行来说，它非常靠近海岸。其次，采用变分贝叶斯独立分量分析（vbICA）方法对大地应变时间变化进行建模，有效地分离了非构造源和构造源的大地应变信号。通过对与这些瞬态现象相关的大逆冲独立分量的滑移进行线性反演，获得了慢滑事件的运动学。该程序允许在空间和时间上与地震活动相匹配的64个sse的检测和建模。地震波和地震发生在离海岸线较远的内陆，与地幔楔角的估计位置密切相关。介于大逆冲构造锁止部分和地震带之间的过渡带，以长期滑动速率相当稳定地蠕动，可能缓冲了sse对大逆冲构造发震部分的影响。
In this study, we model geodetic strain accumulation along the Cascadia subduction zone between 2007.0 and 2017.632 using position time series from 352 continuous GPS stations. First, we use the secular linear motion to determine interseismic locking along the megathrust. We determine two end member models, assuming that the megathrust is either a priori locked or creeping, which differ essentially along the trench where the inversion is poorly constrained by the data. In either case, significant locking of the megathrust updip of the coastline is needed. The downdip limit of the locked portion lies ∼ 20–80 km updip from the coast assuming a locked a priori, but very close to the coast for a creeping a priori. Second, we use a variational Bayesian Independent Component Analysis (vbICA) decomposition to model geodetic strain time variations, an approach which is effective to separate the geodetic strain signal due to non-tectonic and tectonic sources. The Slow Slip Events (SSEs) kinematics is retrieved by linearly inverting for slip on the megathrust the Independent Components related to these transient phenomena. The procedure allows the detection and modelling of 64 SSEs which spatially and temporally match with the tremors activity. SEEs and tremors occur well inland from the coastline and follow closely the estimated location of the mantle wedge corner. The transition zone, between the locked portion of the megathrust and the zone of tremors, is creeping rather steadily at the long-term slip rate and probably buffers the effect of SSEs on the megathrust seismogenic portion.