Focal mechanisms of deep low-frequency earthquakes in eastern shimane in western Japan
Focal mechanisms of deep low-frequency earthquakes in eastern shimane in western Japan
复制标题
日本西部岛根东部深部低频地震的震源机制
DOI：
10.1002/2013jb010681
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Aso. N. and S. Ide
中科院分区：
文献类型：
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作者：
加治俊之;横山翔竜;ソーンピパットポン チャーノン;吉川純一;古澤明;前田京剛;Aso. N. and S. Ide
深层低频地震（LFE）是发生在~10-45 km深度的小地震（M< 2），地震波辐射主要在2-8 Hz频率范围内。日本西部的LFEs分为南海俯冲带的构造LFEs、活火山下方的火山LFEs和远离活火山但与火山LFEs相似的半火山LFEs。虽然构造LFE被认为反映了板块边界上的剪切滑动，但火山和半火山LFE的机制仍不清楚。我们已经确定了岛根东部38个半火山LFE的机制，这是日本最频繁的半火山LFE活动的网站。对于每一个事件，在五个台站的速度地震图反演成一个震源机制和矩率函数相结合的网格搜索和线性反演分析。计算了一维结构的合成波形，并使用深震体波校正了局部场地放大效应。发现估计的矩率函数经常在正值和负值之间振荡，这与常规地震的矩率函数不同。许多低频地震的震源机制主要是一个补偿线性矢量偶极子，其对称轴平行于由震源分布和区域应力最小主轴方向形成的线理。
Deep low‐frequency earthquakes (LFEs) are small earthquakes (M< 2) that occur at depths of ~10–45 km with seismic wave radiation mainly in the frequency range of 2–8 Hz. LFEs in western Japan are categorized into tectonic LFEs in the Nankai subduction zone, volcanic LFEs beneath active volcanoes, and semi‐volcanic LFEs that occur far from active volcanoes but are otherwise similar to volcanic LFEs. While tectonic LFEs are considered to reflect shear slip on a plate boundary, the mechanisms of volcanic and semi‐volcanic LFEs remain unclear. We have determined the mechanisms of 38 semi‐volcanic LFEs in eastern Shimane, which is the site of the most frequent semi‐volcanic LFE activity in Japan. For each event, velocity seismograms at five stations were inverted into a focal mechanism and moment rate function by a combined grid search and linear inversion analysis. Synthetic waveforms were calculated for a one‐dimensional structure and the local site amplification effects were corrected using body waves from deep earthquakes. The estimated moment rate function was found to often oscillate between positive and negative values, which are unlike those of regular earthquakes. The focal mechanisms for many LFEs are dominated by a compensated linear vector dipole with symmetry axes parallel to the lineation formed by the hypocenter distribution and the direction of the minimum principal axis of regional stress.