Remote triggering of non-volcanic tremor in southern Taiwan
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摘要: 选取2011—2016年发生的38次震中距大于1 000 km的MW≥7.5地震震后3小时的连续波形资料，利用人工检视方法对这38次地震是否触发了我国台湾地区的非火山型微震颤进行了调查。分析结果显示：这38次地震中有4次远震触发了非火山型微震颤，事件持续300—500 s不等。利用网格搜寻方法对此4次微震颤事件进行了定位，确定震中位于台湾中央山脉南段，震源深度为21—53 km。结合研究区内地球物理观测资料，分析认为是由于远震产生的面波改变了研究区内的瞬时应力，进而导致断层蠕滑触发了微震颤事件。Abstract: We selected three-hour continuous waveforms after 38 MW≥7.5 earthquakes with epicentral distance larger than 1 000 km during 2011 to 2016 in Taiwan region of China to investigate whether it has triggered non-volcanic tremors （NVTs） by using visual identification. Out of the 38 earthquakes, we identified four teleseismic events which triggered NVTs with duration ranging from 300 s to 500 s. Using grid search, four tremor sources were located in the southern Central Range in Taiwan and the focal depth ranges from 21 to 53 km. Based on the local geophysical observation data, we proposed that the transient stress change induced by surface wave of large teleseisms could lead to the fault creep, which is the critical factor for tremor generation.
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Keywords:
- non-volcanic tremor /
- dynamic stress /
- surface wave triggering /
- Taiwan region
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图 1 研究区域的构造背景及台站和非火山型微震颤（NVT）事件分布
（a） 研究区台站和NVT震中分布；（b） 区域构造背景；（c） 触发NVT的4次地震位置示意图；（d） AA′ 剖面上的NVT事件的震源深度分布
Figure 1. Tectonic settings and distribution of stations and non-volcanic tremor （NVT） locations
（a） Distribution of seismic stations and locations of NVTs；（b） Regional tectonic settings；（c） Schematic diagram for location of four earthquakes that triggered NVT；（d） Distribution of NVT depths along the cross-section AA′
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图 2 2011年东日本MW9.1地震波形频谱分析图
（a） TPUB台站记录到的地震原始波形；（b） 2—8 Hz滤波后波形；（c） 频谱图
Figure 2. The spectrogram of Tohoku earthquake on 11 March 2011
（a） Broad-band seismogram recorded at station TPUB；（b） 2−8 Hz bandpass-filtered seismogram； （c） The spectrogram of seismogram at station TPUB
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图 3 4次NVT事件的定位示意图
（a） 东日本MW9.1地震触发事件；（b） 苏门答腊MW8.6地震触发事件；（c） 所罗门群岛MW7.6地震触发事件；（d） 尼泊尔MW7.9地震触发事件
Figure 3. The schematic diagrams of locating four NVT events
（a） NVT triggered by MW9.1 Tohoku earthquake；（b） NVT triggered by MW8.6 Sumatra earthauake； （c） NVT triggered by MW7.6 Solomon earthquake；（d） NVT triggered by MW7.9 Nepal earthquake
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图 4 2011年3月11日东日本大地震触发的NVT事件波形图
（a） 各台站南北向分量2—8 Hz带通滤波后的波形图，波形左侧为台站名及其距NVT震源距离；（b） 仪器校正后距离NVT震源最近台站的径向、垂向、切向的波形及滤波后波形，红色、黑色箭头分别指勒夫波（4.1 km/s）和瑞雷波（3.5 km/s）理论到时，下同
Figure 4. Tremor triggered by the Tohoku earthquake on 11 March 2011
（a） The 2−8 Hz bandpass-filtered seismograms of N-S component， The hypocentral distance between each station and tremor source is shown next to the station name on left of each trace；（b） The radial，vertical and transverse component seismograms，in which instrument response has been removed，recorded at the nearest station and bandpass-filtered seismograms The red and black vertical arrows indicate the predicted arrivals of the Love and Rayleigh waves with the apparent velocity of 4.1 and 3.5 km/s，respectively，the same below
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图 5 2012年4月11日苏门答腊岛地震触发NVT事件波形图
（a） 各台站南北向分量2—8 Hz带通滤波后的波形图；（b） 仪器校正后距离NVT震源最近台站的径向、垂向、切向的波形及滤波后波形
Figure 5. Tremor triggered by the Sumatra earthquake occurred on 11 April 2012
（a） The 2−8 Hz bandpass-filtered seismograms of N-S component；（b） The radial，vertical and transverse component seismograms，in which instrument response has been removed，recorded at the nearest station and bandpass-filtered seismograms
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图 6 2014年4月12日所罗门群岛地震触发的NVT事件波形图
（a） 各台站南北向分量2—8 Hz带通滤波后的波形图；（b） 仪器校正后距离NVT震源最近台站的径向、垂向、切向的波形及滤波后波形
Figure 6. Tremor triggered by the Solomon earthquake on 12 April 2014
（a） The 2−8 Hz bandpass-filtered seismograms of N-S component；（b） The radial，vertical and transverse component seismograms，in which instrument response has been removed，recorded at the nearest station and bandpass-filtered seismograms
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图 7 2015年4月25日尼泊尔地震触发的NVT事件波形图
（a） 各台站南北向分量2—8 Hz带通滤波后的波形图；（b） 仪器校正后距离NVT震源最近台站的径向、垂向、切向的波形及滤波后波形
Figure 7. Tremor triggered by the Nepal earthquake on 25 April 2015
（a） The 2−8 Hz bandpass-filtered seismograms of N-S component；（b） The radial，vertical and transverse component seismograms，in which instrument response has been removed，recorded at the nearest station and bandpass-filtered seismograms
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图 8 TPUB台站记录到的大地震径向 （a）、垂向 （b） 和切向 （c） 分量的PGV、动态应力及信噪比分布图
背景噪声分析时窗长度为远震事件发震前600 s
Figure 8. The scattergram of PGV，dynamic stress and signal-to-noise ratio for the radial （a），vertical （b） and tangential （c） components of the earthquakes recorded by the station TPUB
The ambient noise level of each event is calculated from a 600 s time window before the occurrence of each main shock
表 1 台湾地区一维速度模型（Wu et al，2007）
Table 1 1-D velocity model in Taiwan region （Wu et al，2007）
vP/（km·s−1） vP/vS vS/km·s−1 深度范围/km vP/（km·s−1） vP/vS vS/km·s−1 深度范围/km 3.82 1.74 2.20 0—2 6.13 1.75 3.50 21—25 4.93 1.68 2.93 2—4 6.25 1.71 3.65 25—30 5.51 1.70 3.24 4—6 6.54 1.73 3.78 30—35 5.63 1.70 3.31 6—9 7.03 1.75 4.02 35—50 5.83 1.76 3.31 9—13 8.00 1.74 4.60 50—70 5.99 1.75 3.42 13—17 8.34 1.73 4.82 70—80 6.06 1.75 3.46 17—21 
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表 2 触发NVT的四次远震事件信息概要
Table 2 General information of the four NVT-triggered teleseismic events
发震时间 地点 震中位置 震源深度/km MW 震中距/° TPUB台站
反方位角/°年−月−日 时：分：秒 北纬/° 东经/° 2011−03−11 5：47：32.8 日本本州岛东岸近海 37.52 143.05 20.0 9.1 23.893 48 2012−04−11 8：39：31.4 苏门答腊岛北部西岸远海 2.35 92.82 45.6 8.6 34.049 236 2014−04−12 20：14：49.9 所罗门群岛 11.35 162.24 27.3 7.6 53.327 126 2015−04−25 6：11：58.6 尼泊尔 27.91 85.33 12.0 7.9 32.092 286 注：表中震中距是以TPUB台站为标准计算得到的。
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