Focal mechanism of the Tokachi-Oki earthquake of may 16, 1968: Contortion of the lithosphere at a junction of two trenches
Focal mechanism of the Tokachi-Oki earthquake of may 16, 1968: Contortion of the lithosphere at a junction of two trenches
复制标题
1968 年 5 月 16 日十胜冲地震的震源机制：两个海沟交界处岩石圈的扭曲
DOI：
10.1016/0040-1951(71)90063-1
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发表时间：
1971
期刊：
影响因子：
2.9
通讯作者：
H. Kanamori
中科院分区：
文献类型：
--
作者：
H. Kanamori
基于纵波初动、横波极化角和长周期面波资料，研究了1968年十胜冲地震（Ms∼8.0）及其余震的震源机制。主要目标是了解两个海沟交界处海洋岩石圈变形的性质。主震被解释为具有相当大走滑分量的低角度逆冲断层，海洋侧向大陆下方俯冲。这种类型的断层活动在西北太平洋带的其他大地震中很常见，被认为代表了该地区的主要构造运动。最大余震（Ms≈7.5）发生在主震后约 10 小时，表明存在滑移方向几乎与主震相反的断层。其他余震分为主震类型或最大余震类型。提出了一个简单的模型来解释这种不寻常的余震序列。在这个模型中，两个海沟（分别是千岛海沟和日本海沟）交界处的下冲岩石圈的扭曲起着关键作用。由于岩石圈的这种扭曲，1968 年十胜冲地震的震源区与 1952 年十胜冲地震发生的邻近区域发生机械相互作用。这种相互作用会导致余震，其断层方向与主震相反。主震震源参数如下：平面（断层面）倾角=20°，倾角方向=S66°W；平面b倾角 = 78°，倾角方向 = S60°E；地震矩=2.8·1028dyn·cm；滑移位错 = 4.1 毫米；应力降=32巴；应变降=0.71·10−4；应变能释放（假设残余应变为零）= 1.0·1024erg。在这些计算中，断层尺寸和刚度分别假设为100×150 km2和4.5·1011dyn/cm2。
The focal mechanism of the Tokachi-Oki earthquake of 1968 (Ms∼ 8.0) and its aftershocks is studied on the basis of P-wave first motion, S-wave polarization angle, and long-period surface-wave data. The major objective is to understand the nature of the deformation of the oceanic lithosphere at a junction of two trenches. The main shock is interpreted as a low-angle thrust fault with a considerable strike-slip component, the oceanic side underthrusting beneath the continent. This type of faulting is common with other great earthquakes of the northwestern Pacific belt, and is considered to represent a major tectonic movement in this region. The largest aftershock (Ms≈ 7.5), that occurred about 10 hours after the main shock, suggests a faulting in which the slip direction is almost opposite to that of the main shock. Other aftershocks are grouped into either the main shock type or the largest aftershock type. A simple model is proposed to explain this unusual aftershock sequence. In this model a contortion of the underthrusting lithosphere at a junction of two trenches, the Kurile and the Japan trenches respectively, plays a key role. Because of this contortion of the lithosphere, the source region of the 1968 Tokachi-Oki earthquake interacts mechanically with a neighboring region where the 1952 Tokachi-Oki earthquake occured. This interaction causes aftershocks whose faulting is in a direction opposite to that of the main shock. The source parameters of the main shock are as follows: planea(fault plane) dip angle = 20°, dip direction = S66°W; planebdip angle = 78°, dip direction = S60°E; seismic moment = 2.8·1028dyn·cm; slip dislocation = 4.1 mm; stress drop = 32 bar; strain drop = 0.71·10−4; strain energy release (residual strain is assumed to be zero) = 1.0·1024erg. In these calculations, the fault dimension and the rigidity are assumed to be 100 × 150 km2and 4.5·1011dyn/cm2respectively.