Seismotectonic analysis of the Tjörnes Fracture Zone, an active transform fault in north Iceland
Seismotectonic analysis of the Tjörnes Fracture Zone, an active transform fault in north Iceland
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冰岛北部活动转换断层 Tjörnes 断裂带的地震构造分析
DOI：
10.1029/98jb02789
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发表时间：
1998
影响因子：
--
通讯作者：
R. Slunga
中科院分区：
文献类型：
--
作者：
S. Rögnvaldsson;Agust Gudmundsson;R. Slunga
Tjornes断裂带是连接Kolbeinsey山脊与冰岛北部裂谷带的转换断裂。主要的转换运动发生在胡萨维克-弗拉蒂断层上，这是一条7-9迈尔古老的主要右行断层。除了这条断层外，与Tjornes断裂带有关的还有两个主要的地震线性构造：Grimsey直线构造和Dalvik直线构造。这些线性构造以地震活动集中为标志，最大地震达到7级。地震的最大深度为10-12公里，并随着距离扩张轴的距离而增加。我们确定了主要地震线上62个震群中800多个地震的准确相对位置和震源机制。大多数重新定位地震的估计相对位置不确定性为2-20m。假设通过每个震群的最佳拟合面与地震组的断裂面重合。对于Husavik-Flatey断层附近的断层群，断层面是右侧的，走向为N122°E-N140°E，类似于Husavik-Flatey断层的总体走向。这与断层上的右旋位移以及与主断层相关的许多转换平行的右旋断层的现场观测是一致的。相比之下，格里姆西和达尔维克线状构造上的地震丛集定义了(主要)大致南北走向的左侧平面，即与这些线状构造的总体趋势成40°-90°的左侧平面。野外观测表明，在达尔维克构造的陆地部分，左侧、南北走向的断裂面也很常见。不同的断裂样式可能代表了不同发育阶段的转换断层。
The Tjornes Fracture Zone is a transform fault connecting the rift zone of the Kolbeinsey Ridge with that of north Iceland. The main transform motion takes place on the Husavik-Flatey Fault, a major 7–9 Myr old right-lateral fault. In addition to this fault, there are two major seismic lineaments associated with the Tjornes Fracture Zone; the Grimsey lineament and the Dalvik lineament. These lineaments are marked by concentrations of seismicity with the largest earthquakes reaching magnitude 7. The maximum depth of earthquakes is 10–12 km and increases with distance from the spreading axis. We determined accurate relative locations and focal mechanisms of more than 800 earthquakes in 62 clusters on the principal seismic lineaments. The estimated relative location uncertainty for most of the relocated earthquakes is 2–20 m. The best fitting plane through each cluster is assumed to coincide with the fault plane of the group of earthquakes. For clusters near the Husavik-Flatey Fault the fault planes are right-lateral and strike N122°E–N140°E, similar to the overall strike of the Husavik-Flatey Fault. This agrees with the right-lateral displacement on the fault as well as with field observations of numerous transform-parallel right-lateral faults associated with the main fault. By contrast, earthquake clusters on the lineaments of Grimsey and Dalvik define (mostly) left-lateral planes striking roughly north-south, i.e., at 40°–90° to the overall trend of these lineaments. Field observations show that left-lateral, north-south trending fault planes are also common in the on-land parts of the Dalvik lineament. The different style of faulting probably represents transform faults at different stages of development.