国产OBS的时间矫正方法——以2019年台湾海峡地壳结构海陆探测实验为例
金震, 博士, 厦门地震勘测研究中心, 主要从事地球深部构造方面的研究, E-mail: 358450071@qq.com |
收稿日期: 2019-07-15
要求修回日期: 2019-09-23
网络出版日期: 2020-05-19
基金资助
地震行业科研专项项目(2015419015)
国家自然科学基金项目(41474071)
地震科技星火计划项目(XH1015)
版权
Correction of made-in-China OBS raw data based on 2019 Fujian and Taiwan Straits crustal structures in sea-land exploration experiments
Received date: 2019-07-15
Request revised date: 2019-09-23
Online published: 2020-05-19
Supported by
Special scientific research projects in the seismic industry(2015419015)
National Natural Science Foundation of China(41474071)
Seismic Science and Technology Spark Program(XH1015)
Copyright
时间服务系统对利用走时层析成像方法进行地下介质速度结构反演至关重要。海底地震仪(ocean bottom seismometer, OBS)工作期间由于没有GPS时间接入, 其时间误差(包括守时误差和授时误差)主要来源于内部石英晶振的准确程度, 受到外部环境变化以及开关机等因素影响。长期实践发现, 部分国产OBS在记录气枪信号以及天然地震信号时存在较大的时间偏差。本文对2019年福建及台湾海峡地壳结构海陆探测实验所获得的53台次国产OBS记录进行了时间服务系统矫正。其中, 针对OBS授时误差, 利用出海前不中断采集的一致性试验和运输船运输过程中产生的晃动互相关进行时间矫正; 针对守时误差, 采用计算实际采样频率与理论采样频率偏差进行矫正; 通过对比矫正前后OBS记录到的天然地震信号, 进行秒级别的检测。结果表明, 经过以上步骤矫正的OBS数据, 其时间记录的准确性得到了显著提高, 从而降低了震相识别、走时拾取的时间误差, 为标准化国产OBS数据采集作业流程提供了重要参考。
关键词: 海陆联测; 海底地震仪(OBS); OBS时间矫正; 天然地震记录
金震 , 郭晓然 , 陈方颖 . 国产OBS的时间矫正方法——以2019年台湾海峡地壳结构海陆探测实验为例[J]. 热带海洋学报, 2020 , 39(3) : 42 -48 . DOI: 10.11978/2019064
Time service system is very important for inverting velocity structure of underground media via traveltime tomography. Due to the lack of GPS time access, the time errors (including time service error and time keeping errors) of the Ocean Bottom Seismometer (OBS) mainly come from the inaccuracy of internal quartz crystal oscillator, affected by external environment changes and switching and other factors. The long term practice finds that, some Chinese-made OBSs have large time deviation when recording air gun signals and natural seismic signals. In this study, 53 Chinese OBS records obtained from the crustal structure sea-land exploration experiments in Fujian and Taiwan straits in 2019 were used for time service system correction. To obtain OBS time service error, the consistency test of uninterrupted acquisition before going to the sea, as well as the sloshing caused by the transport ship during transportation, are used to correct the timing error by cross-correlation. For the time keeping error, the deviation between the calculated actual sampling frequency and the theoretical sampling frequency is corrected. The time service system is corrected comprehensively by using naturally occurred earthquakes. It has been demonstrated that the corrected OBS data can improve the accuracy of time record and reduce the error of seismic phase identification and traveltime picking. At the same time, the results of this paper provide important reference for the widespread use of domestic OBS and standardization of domestic OBS data acquisition process.
图1 研究区域构造背景及观测红色虚线为断层, 黑色实线为走航测线, 蓝色圆点为OBS位置, 红色圆圈为天然地震, 黑色五角星为本次实验探测目标M6.2级地震位置, 绿色五角星为实验过程中OBS记录到的天然地震位置。图中地图来自Python Basemap软件自带底图 Fig. 1 Geological background and distribution of OBS stations used in this study. Black dashed box shows outline of study area, the red lines denote fault, the black lines denote the ship sailed track, the blue dots denote OBS stations, the black cycle denote earthquake location, the red star denotes the location of M6.2 earthquake, and the green stars denote the locations of M5.8 and M3.8 earthquakes |
图6 同一条船不同型号OBS时间矫正前后的振幅对比Fig. 6 Comparison of amplitude before and after time correction of instruments from different manufacturers of the same ship (left: before; right: after) |
图10 时间服务矫正前后3.8级天然地震信号Fig. 10 Natural earthquake signal with M3.8 before and after time service correction |
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