Dynamically Triggered Changes of Plate Interface Coupling in Southern Cascadia
Dynamically Triggered Changes of Plate Interface Coupling in Southern Cascadia
复制标题
DOI：
10.1029/2019gl084395
复制
发表时间：
2019-11-21
影响因子：
5.2
通讯作者：
Buergmann, Roland
中科院分区：
文献类型：
--
作者：
Materna, Kathryn;Bartlow, Noel;Buergmann, Roland
在南卡斯卡迪亚，全球导航卫星系统大约15年的精确测量结果显示，由于卡斯卡迪亚巨型逆冲断层的锁定，稳定变形被大地震和间歇性震颤和滑动事件造成的瞬时变形所打断。然而，在门多西诺三重结附近，我们发现了几个突然的GNSS速度变化，反映了不同的过程。在对地震和季节性负荷进行校正后，我们发现几十个GNSS时间序列显示出类似于2 mm/年的空间相干东西向速度变化，并且这些变化与区域M > 6.5地震在时间上一致。我们考虑了几个假设，并提出动态触发的变化，大推力耦合最好的解释数据。我们的反演定位的耦合变化轻微上倾的震颤生产区。我们推测，流体交换周围的震颤区域可能是重要的。这种瞬态耦合变化的观测是罕见的，很难从机械上解释，但对断层上的地震过程有重要的影响。简明语言摘要在俯冲带中，俯冲界面上的摩擦锁定产生了每年的地表变形，这种变形可以用GPS测量。在地震周期的震间期间，大地震之间持续数百年，这些地面运动通常随时间而恒定，因为板块界面上的锁定相对不变。然而，在北方加州的门多西诺三重连接处，我们发现了过去十年内GPS震间运动轻微变化的证据，这挑战了震间变形恒定的假设。我们的研究结果表明，卡斯卡迪亚俯冲带南部的地震间耦合的变化。有趣的是，这些耦合变化似乎与大型近海地震有关，可能是由这些事件期间的地震震动触发的。这些结果对我们理解俯冲带的地震危险性具有重要意义。
In Southern Cascadia, precise Global Navigation Satellite System (GNSS) measurements spanning about 15 years reveal steady deformation due to locking on the Cascadia megathrust punctuated by transient deformation from large earthquakes and episodic tremor and slip events. Near the Mendocino Triple Junction, however, we recognize several abrupt GNSS velocity changes that reflect a different process. After correcting for earthquakes and seasonal loading, we find that several dozen GNSS time series show spatially coherent east-west velocity changes of similar to 2 mm/yr and that these changes coincide in time with regional M > 6.5 earthquakes. We consider several hypotheses and propose that dynamically triggered changes in megathrust coupling best explain the data. Our inversions locate the coupling changes slightly updip of the tremor-producing zone. We speculate that fluid exchange surrounding the tremor region may be important. Such observations of transient coupling changes are rare and challenging to explain mechanistically but have important implications for earthquake processes on faults.Plain Language Summary In subduction zones, frictional locking on the subduction interface produces year-by-year surface deformation that is measurable with GPS. During the interseismic period of the earthquake cycle, lasting hundreds of years between major earthquakes, these ground motions are usually constant with time because the locking on the plate interface is relatively unchanging. However, at the Mendocino Triple Junction in Northern California, we find evidence for slight changes in GPS interseismic motion within the last decade that challenge the assumption of constant interseismic deformation. Our results suggest changes in interseismic coupling on the southern most Cascadia Subduction Zone. Interestingly, these coupling changes appear to be related to large offshore earthquakes and are perhaps triggered by the seismic shaking during those events. These results have important implications for our understanding of seismic hazard in subduction zones.