Deep low-frequency earthquakes (LFEs) in Northeast Japan occur beneath active volcanoes at depths of 10–40 km. These volcanic LFEs radiate low-frequency seismic waves, with most energy at 2–8 Hz, despite their low magnitudes (M < 2). Although many previous studies have obtained various focal mechanisms with non-double-couple components and suggested physical processes related to magma, the universal physical process is poorly understood. Therefore, we comprehensively determined the focal mechanisms of 264 LFEs for 26 volcanic regions in Northeast Japan using S/P amplitude ratios. Many of the obtained solutions have large double-couple components with small compensated linear vector dipole components. Such source mechanisms can be explained by shear slip on the bending fault. We observed that the plunge of the null axis is as small as 20–30º at depths of 15–25 km, whereas it becomes larger and more varied at depths of 25–35 km. We interpreted that the regional stress field is relatively homogeneous in the middle of the crust, whereas it may be altered near the Moho discontinuity due to thermal stress or other effects related to potential magmatic processes. In addition, after quantitatively investigating the possible triggering of LFEs due to static stress changes in both the 2008 Iwate-Miyagi earthquake and the 2011 Tohoku earthquake, we concluded that LFEs might have been triggered by substantial stress changes caused by large earthquakes in some regions.

中文翻译：

---

日本东北部火山深低频地震的深度相关震源机制

日本东北部的深低频地震 (LFE) 发生在活火山下方 10-40 公里深处。这些火山 LFE 辐射低频地震波，大部分能量在 2-8 Hz，尽管它们的震级较低 (M < 2)。尽管之前的许多研究已经获得了具有非双偶分量的各种震源机制并提出了与岩浆相关的物理过程，但对普遍的物理过程知之甚少。因此，我们利用S/P综合确定了日本东北部 26 个火山区 264 个 LFE 的震源机制。幅度比。许多获得的解决方案具有大的双耦合分量和小的补偿线性矢量偶极子分量。这种源机制可以用弯曲断层上的剪切滑移来解释。我们观察到零轴的俯冲在 15-25 公里的深度小至 20-30º，而在 25-35 公里的深度则变得更大且变化更大。我们认为区域应力场在地壳中部相对均匀，而在莫霍面不连续面附近可能由于热应力或与潜在岩浆过程相关的其他影响而发生改变。此外，在定量调查了 2008 年岩手 - 宫城地震和 2011 年东北地震中静应力变化可能触发 LFEs 后，