Seismicity Properties of the Chain Transform Fault Inferred from OBS Data Obtained from the PI-LAB Experiment
Seismicity Properties of the Chain Transform Fault Inferred from OBS Data Obtained from the PI-LAB Experiment
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根据 PI-LAB 实验获得的 OBS 数据推断的链变换断层的地震活动特性
DOI：
10.1002/essoar.10509002.1
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Leptokaropoulos K
中科院分区：
文献类型：
--
作者：
Leptokaropoulos K
海洋转换断层（TF）由一级不连续性组成，在洋中脊扩展中心之间形成边界。TF主要容纳走滑运动，分隔不同年龄和热结构的岩石圈板块。海洋性TF的有趣之处在于，由于其长度很长，它们不会产生像预期的那么大的地震，地震滑动只对应于总构造滑动的一小部分。海洋环流相对地质上的简单性意味着它们是更危险的大陆环流的重要模拟物，在提高对地震周期的认识方面具有很大的潜力。结合微震和远震资料，研究了赤道MAR中一条~300 km长的TF链上的地震特征。本文利用PI-LAB（岩石圈-软流圈边界被动成像）实验和EURO-LAB（流变岩石圈-软流圈边界挖掘实验）收集的近1年微震活动数据（共812次）。我们在多维相空间中进行聚类分析，包括各种地震（震中坐标，震级）和地球物理（重力异常，测深，潮汐高度）参数。我们研究了潜在的触发机制，包括潮汐、静态和动态应力。我们通过考虑1976年以来全球质心矩张量（GCMT）的强地震（MW>~5.0）来扩展我们的分析。我们从分析中发现了三个独特的50-100公里长的集群或片段，从东到西，被地震间隙隔开。微震活动最活跃的是链东段，那里有最大的正花构造，负rMBA重力异常，但很少有M>5.5事件。相对于东部，西段的地震活动率较低，并与正的rMBA和一些小的花状结构有关。中央段位于两个地震间隙之间，在中间显示出相对较高的活动率。研究结果表明，东部花构造中热液循环引起的高蚀变地幔/地壳反压和/或高孔隙压力增强了地震活动性。总体而言，我们发现存在连续的锁定和爬行片段，其中一些斑块表现出杂交行为，可能导致它们的零星激活/再激活。
Oceanic Transform Faults (TF) comprise first order discontinuities bounded between mid-ocean ridge spreading centres. TF mainly accommodate strike slip motion, separating lithospheric plates of different age and thermal structure. Oceanic TF are intriguing in that they do not produce earthquakes as large as might be expected given their long length, with seismic slip corresponding only to a small fraction of the total tectonic slip. The relative geologic simplicity of oceanic TF means that they are an important analogue for more hazardous continental TF, with high potential for improving insights into the earthquake cycle. We investigate the earthquake properties along Chain, a ~300 km long TF in the equatorial MAR by combining both microseismic and teleseismic data. We use the ~1-year microseismicity data (total of 812 events) gathered during the PI-LAB (Passive Imaging of the Lithosphere-Asthenosphere Boundary) experiment and EURO-LAB (Experiment to Unearth the Rheological Lithosphere-Asthenosphere Boundary). We perform cluster analysis in multi-dimensional phase space, consisting of various seismic (epicentral coordinates, magnitude) and geophysical (gravity anomalies, bathymetry, tidal height) parameters. We investigate potential triggering mechanisms, including tidal, static and dynamic stresses. We extend our analysis back in time by considering stronger earthquakes (MW>~5.0) from Global Centroid Moment Tensor (GCMT) since 1976. We find three unique, 50-100 km long clusters or segments from our analysis going from east to west, separated by seismic gaps. Microseismic activity is highest at the eastern segment of Chain where there is the largest positive flower structure, negative rMBA gravity anomaly but very few M>5.5 events. The western segment has reduced seismicity rates relative to the eastern, and is associated with a positive rMBA and a few small flower structures. The central segment is bounded between two seismic gaps and demonstrates relatively high activity rates in the middle. Our result suggests that trans-pression of highly altered mantle/crust and/or high pore pressure due to hydrothermal fluid circulation in the eastern flower structure enhances seismic activity. Overall, we find the existence of consecutive locking and creeping segments, with some of the patches exhibiting hybrid behaviour, potentially causing their sporadic activation/reactivation.
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