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Tomography of the southern Taiwan subduction zone and possible emplacement of crustal rocks into the forearc mantle

机译：台湾南部俯冲带的层析成像以及可能的地壳岩石进入前地幔

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This paper investigates velocity structure of the active plate boundary in southern Taiwan by joint analysis of gravity anomaly and seismic arrival time data. P and S-P arrival time data from 3238 earthquakes were used. In addition to CWBSN permanent networks, seismic data include the Central Weather Bureau permanent networks and a temporary network consisting of 11 ocean bottom seismometers (OBSs) that was deployed to detect the aftershocks of the 2006 (M_L7.1) Henchun earthquake occurred beneath southern Taiwan. The total available OBS data set consists of～700 detected earthquakes, from which around 500 could be well located where about 450 events have been used in simultaneous inversion for hypocenters, three-dimensional Vp and Vp/Vs models for the study area. The main objective of incorporating gravity analysis is used to improve the velocity model for the offshore area, where it is poorly sampled by local earthquakes. This study found a low-velocity zone existing above the subducting South China Sea slab in the mantle wedge. Based on gravity modeling and our resulting velocity and Poisson's ratio models suggest that the subduction complex, which is characterized with a low P-wave velocity and low Poisson's ratios beneath the southern Taiwan. This duplex structure is characterized by a zone of low P-wave velocities in the range of 6.2-6.8 km/s between 25 and 40 km depth. It also shows that earthquake hypocenters do not fall within this low velocity zone. We have also used seismic tomography velocities to estimate the volume percentage of serpentinite and silica concentrations in southern Taiwan. The calculated serpentinite is about 30% and the volume percentage of quartz estimated is about 20% at the base of the forearc lower crust.
机译：本文通过重力异常和地震到达时间数据的联合分析，研究了台湾南部活动板块边界的速度结构。使用了3238次地震的P和S-P到达时间数据。除CWBSN永久网络外，地震数据还包括中央气象局的永久网络和由11个海底地震仪（OBS）组成的临时网络，该临时网络被部署用于检测台湾南部下方发生的2006年（M_L7.1）恒春地震的余震。 。可用的OBS数据集总共包括约700个已探测的地震，从中可以很好地定位约500个地震，其中约450个事件已用于震源同时反演，研究区域的三维Vp和Vp / Vs模型。结合重力分析的主要目的是用于改进离岸地区的速度模型，在该区域中，当地地震对它的采样效果很差。这项研究在地幔楔中的俯冲南海板块上方发现了一个低速带。基于重力模型以及我们得出的速度和泊松比模型，表明该俯冲复合物的特征是台湾南部以下的低波速和泊松比低。这种双工结构的特征是在25至40 km深度之间的低P波速度带处于6.2-6.8 km / s的范围内。这也表明地震震源没有落在这个低速度带内。我们还使用地震层析成像速度来估算台湾南部蛇纹岩和二氧化硅浓度的体积百分比。计算得出的蛇纹石约为30％，在前臂下部地壳底部估计的石英体积百分比约为20％。

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