The upper crustal microseismicity image from the North Chilean subduction zone
The upper crustal microseismicity image from the North Chilean subduction zone
复制标题
智利北部俯冲带上地壳微震活动图像
DOI：
10.17169/refubium-7321
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发表时间：
2011
影响因子：
--
通讯作者：
P. S. Reinoso
中科院分区：
文献类型：
--
作者：
P. S. Reinoso
2005年11月，在智利前科迪勒拉地区大约南纬21度安装了一个临时短周期地震网络。这套由12个三分量台站组成的西裂缝地震台网自那时以来一直在连续记录，然而，这里只处理和分析了2005-2009年记录的地壳微震活动数据。因此，智利俯冲带北部弧前区的微震活动性研究可以恢复地壳的重要构造特征。一个新的形象的地壳结构和西裂缝断层系统（WFFS）作为一个向西倾斜的压缩结构，几何反对纳斯卡板块俯冲，已受到微震活动。这种特殊几何形状的起源还没有明确的定义，但这可能是地壳流变行为差异的构造反应。该构造的特征，在其应力分布和运动学方面，已获得了良好的拟合与一些更深的震源机制，并通过应力张量分析在该地区。应力张量分析还表明，收敛边缘的应力状态与压缩有关，而伸展只是与安第斯山脉最高区域有关的局部力的表现。两个地震群也已确定，并可能与一个盲目的分支的WFFS。对这两个团簇进行了研究，重点是它们的来源和与流体运移的可能联系。据观察，在该区域中发现的两个集群的一些特性彼此不同。中央震群具有明显的震相特征，可以清楚地识别，而西南震群具有明显的主震关联，可以分为两个亚震群（分别为A和A '）。相反，相似性允许推断它们可能有共同的起源。两者的b值都是构造板块边界的特征。事件的空间扩展-这是大约局限于一个平面-揭示了一个逐步增长的主要断裂，形成群和子集群A活动。研究还发现，地震本身在其破裂区边界附近触发余震。此外，震源的时空迁移，以及与被解释为流体迁移带的区域的空间相关性，导致相信流体与群和子群A的来源之间存在密切关系。上述观察结果表明，断裂传播的粘滑行为可以通过流体渗透临界载荷断层带中地震引起的应力转移和诱导流体流动来解释。
In November 2005, a temporary short-period seismic network was installed in the Chilean Precordillera, around 21◦S. This set of twelve 3-component stations that form the West Fissure seismological network has been recording continuously since then, however, only the crustal microseismicity data recorded during the years 2005-2009 were processed and analyzed here. Thus, the microseismicity studies in the forearc of the north Chilean subduction have permitted the retrieval of important tectonic features of the crust. A new image of the crustal structure and the West Fissure Fault System (WFFS) as a westward-dipping compressive structure, geometrically opposed to Nazca plate subduction, has been constrained by microseismicity. The origin of this particular geometry is not clearly defined yet, but this could be a tectonic response to differences in the rheological behavior of the crust. The characterization of this structure, in terms of its stress distribution and kinematics, has been obtained by a good fit with some deeper focal mechanisms and also through stress tensor analysis in the zone. The stress tensor analysis also shows that the state of stress in the convergence margin is related to compression, whereas the extension is only a manifestation of local forces associated with the highest areas in the Andes. Two seismic clusters have also been identified and possibly associated with a blind branch of WFFS. The study of these two clusters with a focus on their sources and possible connection with fluid migration was carried out. It is observed that some characteristics of the two clusters found in the zone differ from each other. The central cluster has characteristics of an earthquake swarm with two phases which can clearly be identified, whereas the SW cluster has a clear main shock associated and can be separated into two subclusters (A and A’, respectively). In contrast, the similarities permit to infer that they could have a common origin. The b-values for both are characteristic of tectonic plate boundaries. The spatial spreading of the events –which is approximately confined to one plane– reveals a progressively growing of the main fracture that form the swarm and subcluster A activities. It is also found that earthquakes themselves trigger aftershocks near the border of their rupture areas. In addition, the spatio-temporal migration of hypocenters, as well as, spatial correlation –with areas that were interpreted as fluid migration zones– lead to believe that there is a close relation between fluids and the sources of the swarm and subcluster A. These observations above, point to think in a stick-slip behavior of the rupture propagation, which can be explained by stress transfers and induced fluid flows due to earthquakes in a fluid-permeated critically loaded fault zone.