Seismicity patterns along the Ecuadorian subduction zone: new constraints from earthquake location in a 3-D a priori velocity model
Seismicity patterns along the Ecuadorian subduction zone: new constraints from earthquake location in a 3-D a priori velocity model
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DOI：
10.1093/gji/ggs083
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发表时间：
2013-04-01
影响因子：
2.8
通讯作者：
Theunissen, Thomas
中科院分区：
文献类型：
--
作者：
Font, Yvonne;Segovia, Monica;Theunissen, Thomas
为了提高地震定位，我们创建了一个3-D先验P波速度模型（3-DVM），近似厄瓜多尔俯冲系统的大速度变化。3-DVM是根据地壳和上地幔的结构几何形状和速度特性，从地球物理和地质数据的集成构建的。此外，还进行了具体的台站选择，以弥补安第斯山脉上台站密度高的问题。三维合成实验，然后设计评估网络的能力，以恢复事件的位置，仅使用P到达和MAXI技术。提出了三种合成地震定位实验：（1）无噪波和（2）有噪波用于3-DVM，（3）无噪波用于1-DVM。综合结果表明，在最佳条件下（精确到达数据集和三维虚拟仪器），厄瓜多尔网络的时空配置可以准确地定位俯冲带前部70%的事件（平均方位差为289度± 44度）。噪声P波到达（高达+/- 0.3 s）可以准确定位50%的地震。在1-DVM内处理地震位置几乎从未允许海上地震的准确震源位置（15%），这突出了在俯冲带中使用3-DVM的作用。对于应用程序的真实的数据，从3-D-MAXI目录的地震活动性分布进行了比较，在1-D分层VM中获得的测定。除了高质量的位置不确定性，聚类和深度分布证实了3-D-MAXI目录的可靠性。的地震活动性分布的图案（13年的记录，在地震周期的地震间期间）的破裂带和凹凸的M-W = 7.9 1942年和M-W = 7.7 1958年事件（M-W = 8.8 1906凹凸补丁未定义）的图案进行了比较。我们观察到，1942年，1958年和1906年事件的成核与正简单布格异常的地区和海洋阶地仍然保留在沿海形态的地区相吻合。从北到南：（1）1958年破裂带几乎是地震活动的，属于一个高耦合带;（2）1942年破裂带在加莱拉走向（垂直于海沟）以南，地震活动中等，在孕震板间带上较深，并与贾马群（向南）相邻。该集群正面临着卡波帕萨多盖和积极的布格异常的压倒性的利润。我们怀疑这个集群反映了局部粗糙（部分耦合）的区域。在Jama群以南，巴伊亚地区的球形地震带被解释为具有低地震耦合（稳定蠕变运动或缓慢滑动事件）。我们怀疑产生三个M > 7事件（1896年、1956年和1998年）的地点对应于一小片强耦合。在南部，在曼塔-波多黎各洛佩斯区，地震活动主要是在地震群（1998年，2002年，2005年）。虽然在该地区观察到缓慢滑动事件（Vallee等人提交），但我们从海岸线形状、海洋阶地和高正布格异常推断，这里的地震活动可能揭示了大量的地震耦合。
To improve earthquake location, we create a 3-D a priori P-wave velocity model (3-DVM) that approximates the large velocity variations of the Ecuadorian subduction system. The 3-DVM is constructed from the integration of geophysical and geological data that depend on the structural geometry and velocity properties of the crust and the upper mantle. In addition, specific station selection is carried out to compensate for the high station density on the Andean Chain. 3-D synthetic experiments are then designed to evaluate the network capacity to recover the event position using only P arrivals and the MAXI technique. Three synthetic earthquake location experiments are proposed: (1) noise-free and (2) noisy arrivals used in the 3-DVM, and (3) noise-free arrivals used in a 1-DVM. Synthetic results indicate that, under the best conditions (exact arrival data set and 3-DVM), the spatiotemporal configuration of the Ecuadorian network can accurately locate 70 per cent of events in the frontal part of the subduction zone (average azimuthal gap is 289 degrees +/- 44 degrees). Noisy P arrivals (up to +/- 0.3 s) can accurately located 50 per cent of earthquakes. Processing earthquake location within a 1-DVM almost never allows accurate hypocentre position for offshore earthquakes (15 per cent), which highlights the role of using a 3-DVM in subduction zone. For the application to real data, the seismicity distribution from the 3-D-MAXI catalogue is also compared to the determinations obtained in a 1-D-layered VM. In addition to good-quality location uncertainties, the clustering and the depth distribution confirm the 3-D-MAXI catalogue reliability. The pattern of the seismicity distribution (a 13 yr record during the inter-seismic period of the seismic cycle) is compared to the pattern of rupture zone and asperity of the M-w = 7.9 1942 and the M-w = 7.7 1958 events (the M-w = 8.8 1906 asperity patch is not defined). We observe that the nucleation of 1942, 1958 and 1906 events coincides with areas of positive Simple Bouguer anomalies and areas where marine terraces are still preserved on the coastal morphology. From north to south: (1) the 1958 rupture zone is almost aseismic and is attributed to a zone of high coupling; (2) south of the Galera alignment (perpendicular to the trench), the 1942 rupture zone presents moderate seismicity, deeper on the seismogenic interplate zone, and abutting on the Jama cluster (to the south). This cluster is facing the Cabo Pasado cap and positive Bouguer anomalies on the overriding margin. We suspect that this cluster reflects a zone of local asperity (partial coupling). South of the Jama cluster, the spherical aseismic zone in the Bahia area is interpreted as having a low seismic coupling (steady creep motion or slow slip events). We suspect that the site that generated the three M > 7 events (1896, 1956 and 1998) correspond to a small patch of strong coupling. To the south, in the Manta-Puerto Lopez zone, the seismicity is mainly organized in earthquake swarms (1998, 2002, 2005). Although slow slip events have been observed in the area (Vallee et al. submitted), we infer from the coastline shape, the marine terraces and the high positive Bouguer anomalies that the seismicity here might reveal a significant amount of seismic coupling.