Offshore real‐time ocean bottom networks of seismometers and ocean bottom pressure (OBP) gauges have been recently established such as DONET and S‐net around the Japanese islands. One of their purposes is to practice rapid and accurate tsunami forecasting. Near‐fault OBP records, however, are always contaminated by nontsunami components such as sea‐bottom acceleration change until an earthquake stops its fault or sea‐floor motions. This study proposes a new method to separate tsunami and ocean bottom displacement components from coseismic OBP records in a real‐time basis. Associated with the Off‐Mie earthquake of 2016 April 1, we first compared OBP data with acceleration, velocity, and displacement seismograms recorded by seismometers at common ocean bottom sites in both time and frequency domains. Based on this comparison, we adopted a band‐pass filter of 0.05–0.15 Hz to remove ocean‐bottom acceleration components from the OBP data. Resulting OBP waveforms agree well with the tsunami components estimated by a 100‐s low‐pass filter with records of several hundred seconds in length. Our method requires only an early portion of a given OBP record after 30 s of an origin time in order to estimate its tsunami component accurately. Our method enhances early tsunami detections with near‐fault OBP data; that is, it will make a tsunami forecasting system faster and more reliable than the previous detection schemes that require data away from source regions or after coseismic motions are over.

中文翻译：

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基于与地震数据比较的近断层海底压力计记录的海啸早期检测

最近在日本群岛周围建立了海上实时地震仪和海底压力计（OBP）仪表的海底网络。其目的之一是进行快速准确的海啸预报。但是，直到地震停止断层或海底运动之前，近断层的OBP记录始终会受到海啸等非海啸因素的污染。这项研究提出了一种从同震OBP记录中实时分离海啸和海底位移分量的新方法。与2016年4月1日的米氏地震相关，我们首先将OBP数据与地震仪在时域和频域在普通海底站点记录的加速度，速度和位移地震图进行了比较。根据此比较，我们采用了0.05–0.15 Hz的带通滤波器，从OBP数据中去除了海底加速度分量。产生的OBP波形与100秒低通滤波器估计的海啸分量非常吻合，记录的长度为数百秒。我们的方法只需要在起始时间30 s之后的给定OBP记录的早期部分，即可准确估算其海啸分量。我们的方法利用近断层OBP数据增强了对海啸的早期发现；也就是说，它将使海啸预报系统比以前的探测方案更快，更可靠，前者的探测方案要求数据远离源区域或在同震运动结束之后。产生的OBP波形与100秒低通滤波器估计的海啸分量非常吻合，记录的长度为数百秒。我们的方法只需要在起始时间30 s之后的给定OBP记录的早期部分，即可准确估算其海啸分量。我们的方法利用近断层OBP数据增强了对海啸的早期发现；也就是说，它将使海啸预报系统比以前的探测方案更快，更可靠，前者的探测方案要求数据远离源区域或在同震运动结束之后。所产生的OBP波形与100秒低通滤波器估计的海啸分量非常吻合，记录的长度为数百秒。我们的方法只需要在起始时间30 s之后的给定OBP记录的早期部分，即可准确估算其海啸分量。我们的方法利用近断层OBP数据增强了对海啸的早期发现；也就是说，它将使海啸预报系统比以前的探测方案更快，更可靠，前者的探测方案要求数据远离源区域或在同震运动结束之后。