宽频带海底地震仪的地震重定位对马尼拉俯冲板片形态的约束
中国科学院边缘海与大洋地质重点实验室, 中国科学院南海海洋研究所, 广州 510301
中国科学院南海生态环境工程创新研究院, 广州 510301
中国地震局地震监测与减灾技术重点实验室, 广东省地震局, 广州 510070
中国科学院大学, 地球与行星科学学院, 北京 100049
国家自然科学基金项目（91958212，91428204，41730532，41576070，41676043，41606064），促进海峡两岸科技合作联合基金（U1505232）和国家自然科学基金委员会共享航次（NORC2015-08，NORC2016-08）联合资助
中图分类号:P315,P738
Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou 510301, China
Key Laboratory of Earthquake Monitoring and Disaster Mitigation Technology, China Earthquake Administration, Guangdong Earthquake Agency, Guangzhou 510070, China
College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
将宽频带OBS用于海底天然地震长期观测，在国内尚处于实验阶段.2015年在马尼拉俯冲带北段开展了为期6个月的宽频带海底天然地震观测试验.根据回收的1台海底地震仪（OBS04）与国际地震台网的718台陆地地震台站，共记录到7562个P波走时和5002个S波走时数据，利用Hyposat地震定位方法，对马尼拉俯冲带北部（119°E—123°E，19°N—22°N）在2015年8月至2016年2月期间的264个地震进行了重定位.地震重定位的结果及定位误差分析表明，在海域布设的OBS04台站让地震观测的空间分布更为合理，提高了地震定位精度；重定位后的震中分布更为集中，与地质构造吻合良好；浅部的地震活动较为活跃，分布密集，与浅部断层发育有关；重定位后的4条震源深度投影剖面，从不同角度较好地约束了俯冲板片上边界的板片形态，板片倾角在浅部0~30 km区间约为10°~22°，随着深度的增加，俯冲板片逐渐变陡，在深度120~180 km处倾角约为41°~58°.该项研究为马尼拉俯冲带北段的板片形态提供了重要约束，而且为今后长期天然地震观测提供了重要而宝贵的经验与借鉴.
The broadband Ocean Bottom Seismometer (OBS) observation is still in the experimental stage. One experiment was carried out for 6 months in the northern Manila subduction zone in 2015. We picked 7562 P-wave and 5002 S-wave travel-times recorded by a broadband station (OBS04) and 718 land stations. Totally 264 earthquakes that occurred from August 2015 to February 2016 in the study area (119°E—123°E, 19°N—22°N) were relocated using the Hyposat method. The results show that the hypocenter accuracy has been improved due to the addition of OBS04 deployed near the Manila Trench and reasonable spatial distribution of seismic stations. The hypocenters of relocated earthquakes are much more concentrated and fit well with geological structures than before. Shallow seismic events are dominant and concentrating in this area, which are related to the faults in crust. Four projection profiles of focal depths of relocated earthquakes reveal the upper boundary of the slab in the northern seismic concentrating region. The angles of the subduction slab increase from 10°~22° in the shallow (0~30 km) to 41°~58° in the deep subsurface (120~180 km). This research provides a significant constraint on the slab shape of the northern Manila subduction zone as well as valuable experiences and references for broadband OBS observation in the future.
图 1马尼拉俯冲带北部水深地形与震源机制分布图
马尼拉俯冲带北部水深地形与震源机制分布图
Figure 1.Map showing bathymetry and focal mechanism solutions in the northern Manila subduction zone
Map showing bathymetry and focal mechanism solutions in the northern Manila subduction zone
图 2宽频带OBS的仪器响应频谱
宽频带OBS的仪器响应频谱
Figure 2.Frequency spectrum of the instrument response of the broadband OBS
Frequency spectrum of the instrument response of the broadband OBS
图 3OBS04台站的垂直分量(BHZ)去除仪器响应前后波形记录对比
OBS04台站的垂直分量(BHZ)去除仪器响应前后波形记录对比
Figure 3.Comparison of waveform records of the vertical components (BHZ) of OBS04 before and after removing instrument
Comparison of waveform records of the vertical components (BHZ) of OBS04 before and after removing instrument
图 4地震定位参考的一维速度模型
地震定位参考的一维速度模型
Figure 4.1-D velocity model referenced for earthquake relocation
1-D velocity model referenced for earthquake relocation
图 5OBS04台站记录的一个4.8级近震波形及P波和S波走时拾取
OBS04台站记录的一个4.8级近震波形及P波和S波走时拾取
Figure 5.Waveforms and P- and S-wave travel-time picking from a local earthquake mb=4.8 recorded by OBS04
Waveforms and P- and S-wave travel-time picking from a local earthquake mb=4.8 recorded by OBS04
图 6研究区264个地震事件重定位前后的震中水平分布图
研究区264个地震事件重定位前后的震中水平分布图
Figure 6.Map showing distribution of 264 hypocenters before and after earthquakes relocation
Map showing distribution of 264 hypocenters before and after earthquakes relocation
图 8重定位前后4条剖面的震源深度投影
重定位前后4条剖面的震源深度投影
Figure 8.Focal depth distributions along four profiles(AA′, BB′, CC′ and DD′) before and after earthquake relocation
Focal depth distributions along four profiles(AA′, BB′, CC′ and DD′) before and after earthquake relocation
图 7地震重定位的误差分布图
地震重定位的误差分布图
Figure 7.Error distributions of earthquakes relocation
Error distributions of earthquakes relocation
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Map showing bathymetry and focal mechanism solutions in the northern Manila subduction zone
Frequency spectrum of the instrument response of the broadband OBS
Comparison of waveform records of the vertical components (BHZ) of OBS04 before and after removing instrument
1-D velocity model referenced for earthquake relocation
Waveforms and P- and S-wave travel-time picking from a local earthquake mb=4.8 recorded by OBS04
Map showing distribution of 264 hypocenters before and after earthquakes relocation
Focal depth distributions along four profiles(AA′, BB′, CC′ and DD′) before and after earthquake relocation
Error distributions of earthquakes relocation