Filling the gap in a double seismic zone: Intraslab seismicity in Northern Chile
Filling the gap in a double seismic zone: Intraslab seismicity in Northern Chile
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填补双地震带的空白：智利北部的板内地震活动
DOI：
10.1016/j.lithos.2019.105155
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发表时间：
2019
期刊：
影响因子：
3.5
通讯作者：
S. Hainzl
中科院分区：
文献类型：
--
作者：
C. Sippl;B. Schurr;T. John;S. Hainzl
在地球仪的许多俯冲带中，都存在着中深的实验室内地震活动的双地震带（DSZ），这种双地震带与下地壳和地幔岩石圈的脱水反应有关。这些反应发生在，一阶，恒定的温度，这解释了观察到的线性安排的地震活动，似乎遵循等温线的热models.mediate深度的地震活动在北方智利，然而，表现出的模式intraslab地震活动，大大偏离了一个经典的DSZ。而两个平行的地震活动面存在于板的上倾部分，这些突然变成一个25 - 30公里厚，均匀孕震体在深度为1080 - 100公里。在此深度区间内，地震活动率和地震矩释放显著增加。为了了解哪些过程引起了这种配置，是什么区别于更传统的俯冲带设置（如日本）的北方智利俯冲带，我们进行了详细的地震调查板地震活动在北方智利使用的数据从IPOC永久网络。我们确定了超过600个实验室内地震的矩张量，处理和评估了8年高分辨率地震震源数据的位置不确定性，并对不同的地震活动群体进行了统计分析。我们观察到，在高度活跃的集群和上述DSZ中的地震都表现出一致的下倾广泛的震源机制，与板块的倾角和方向一致。这意味着强大的板块拉力，这也是显而易见的板块陡峭概述的震源对下倾终止的高度活跃的集群。此外，集群中的事件显示出非常弱的余震生产力和高背景事件率，这导致地震活动性的时间分布接近于一个纯粹的随机过程。我们发现，高孕震体的位置在空间上与接收函数图像中洋壳与下伏地幔之间速度差的消失、地震衰减图像中地幔楔的"冷鼻"（即停滞部分）向热部分的转变以及板块倾角的增大相一致。基于这些不同的证据，我们推测，来自上方的高张应力和热输入可能导致动力学延迟变质反应的突然爆发，从而使所观察到的地震活动率增加。由于这些反应总体上有一个负的体积变化，导致板致密化，从而进一步增加板拉，我们观察到的地震活动的空间格局可能是由于失控型过程，这将解释其突然开始和高时刻释放率。
Double seismic zones (DSZs) of intermediate-depth intraslab seismicity are observed in many subduction zones around the globe, and have been related to dehydration reactions in the downgoing crust and mantle lithosphere. These reactions occur at, to first order, constant temperatures, which explains the observed linear arrangements of seismicity that appear to follow isotherms of thermal models.Intermediate-depth seismicity in Northern Chile, however, exhibits a pattern of intraslab seismicity that substantially deviates from a classical DSZ. Whereas two parallel seismicity planes are present in the updip part of the slab, these abruptly change into a 25–30 km thick, homogeneously seismogenic volume at a depth of ∼80–100 km. Seismicity rate and moment release significantly increase in this depth interval. In order to understand which processes evoke this configuration and what distinguishes the Northern Chile subduction zone from more conventional subduction zone settings (e.g. Japan), we performed a detailed seismological investigation of slab seismicity in Northern Chile using data from the IPOC permanent network. We determined >600 moment tensors of intraslab earthquakes, processed and evaluated location uncertainties for 8 years of high-resolution earthquake hypocenter data, and performed statistical analysis of the different seismicity populations.We observe that earthquakes both in the highly active cluster and the DSZ above exhibit consistently downdip extensive source mechanisms that align with the dip angle and direction of the slab. This implies strong slab pull, which is also evident from slab steepening outlined by hypocenters towards the downdip termination of the highly active cluster. Moreover, events in the cluster show a very weak aftershock productivity and a high background event rate, which leads to a temporal distribution of seismicity that is close to a purely random process. We find that the position of the highly seismogenic volume spatially coincides with: 1) the disappearance of the velocity contrast between oceanic crust and the underlying mantle in receiver function images, 2) the transition from the “cold nose” (i.e. the stagnant part) to the hot part of the mantle wedge, as evidenced by seismic attenuation images, and 3) with an increase of the slab dip angle. Based on these different pieces of evidence, we speculate that high tensile stresses and heat input from above could lead to a sudden burst of kinetically delayed metamorphic reactions there that then enables the observed increased seismicity rates. Since these reactions have overall a negative volume change that leads to slab densification and hence further increases slab pull, the spatial pattern of seismicity we observe could result from a runaway-type process, which would explain its abrupt start and high moment release rates.
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DOI：
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发表时间：
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DOI：
10.1130/2015.1212(02
发表时间：
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期刊：
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