Low frequency earthquakes below southern Vancouver Island
Low frequency earthquakes below southern Vancouver Island
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温哥华岛南部以下低频地震
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
S. Peacock
中科院分区：
文献类型：
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作者：
M. Bostock;A. Royer;E. Hearn;S. Peacock
俯冲带中低频地震的性质和分布提供了对闭锁孕震区板块边界形变下倾的认识。我们采用网络自相关检测，以确定LFE家庭下南部温哥华岛和周边地区。在2004年和2005年检测到的初始套件的5775 LFEs在一组选择的7个站被分组为140个家庭使用波形聚类分析。这些系列被用作迭代网络互相关方案中的模板，以检测不同震颤事件中的LFE，合并新的台站，并提高LFE模板信噪比。与日本西南部一样，代表性的LFE位置在实验室内地震活动轨迹上方几公里处定义了一个相对紧密的倾斜表面，位于一个突出的倾斜低速带（LVZ）内。近垂直源-接收器几何形状的LFE极化具有非常均匀的偶极特征，指示点源双耦合激发。由P波初动确定的震源机制以走滑和逆冲断层的组合为特征。我们认为，LFEs和定期intraslab地震活动发生在不同的结构和应力制度。的LVZ，推断为代表弱，超压，多孔和糜棱岩化的变质玄武岩的海洋地壳层2，分离LFEs表现出变形的板块边界剪切带内的intraslab地震产生的张应力和脱水脆化在一个更有能力的下海洋地壳层3和下地幔。
The nature and distribution of low frequency earthquakes (LFEs) in subduction zones provide insight into plate boundary deformation downdip of the locked seismogenic zone. We employ network autocorrelation detection to identify LFE families beneath southern Vancouver Island and environs. An initial suite of 5775 LFEs detected in 2004 and 2005 at a select set of 7 stations is grouped into 140 families using waveform cluster analysis. These families are used as templates within an iterative network cross correlation scheme to detect LFEs across different tremor episodes, incorporate new stations, and improve LFE template signal‐to‐noise ratio. As in southwest Japan, representative LFE locations define a relatively tight, dipping surface several km above the locus of intraslab seismicity, within a prominent, dipping low‐velocity zone (LVZ). LFE polarizations for near‐vertical source‐receiver geometries possess a remarkably uniform dipolar signature indicative of point‐source, double‐couple excitation. Focal mechanisms determined fromP‐wave first motions are characterized by a combination of strike‐slip and thrust faulting. We suggest that LFEs and regular intraslab seismicity occur in distinct structural and stress regimes. The LVZ, inferred to represent weak, overpressured, porous and mylonitized metabasalts of oceanic crustal Layer 2, separates LFEs manifesting deformation within a plate boundary shear zone from intraslab earthquakes generated by tensional stresses and dehydration embrittlement within a more competent lower oceanic crustal Layer 3 and underlying mantle.