Strong‐Motion Broadband Displacements From Collocated Ocean‐Bottom Pressure Gauges and Seismometers

Dense and broad‐coverage ocean‐bottom observation networks enable us to obtain near‐fault displacement records associated with an offshore earthquake. However, simple integration of ocean‐bottom strong‐motion acceleration records leads to physically unrealistic displacement records. Here we propose a new method using a Kalman filter to estimate coseismic displacement waveforms using the collocated ocean‐bottom seismometers and pressure gauges. First, we evaluate our method using synthetic records and then apply it to an offshore Mw 6.0 event that generated a small tsunami. In both the synthetic and real cases, our method successfully estimates reasonable displacement waveforms. Additionally, we show that the computed waveforms improve the results of the finite fault modeling process. In other words, the proposed method will be useful for estimating the details of the rupture mechanism of offshore earthquakes as a complement to onshore observations. Plain Language Summary Ocean‐bottom observations enable us to obtain near‐fault displacement records associated with an offshore earthquake. However, simple integration of ocean‐bottom acceleration records leads to physically unrealistic displacement records. Here we propose a new method to estimate offshore coseismic displacement waveforms. First, we evaluate our method using synthetic records and then apply it to an offshore earthquake that generated a small tsunami. In both cases, our method successfully estimates reasonable displacements. Additionally, we show that the computed waveforms improve the results of the earthquake source modeling process. In other words, the proposed method will be useful for estimating the details of the rupture mechanism of offshore earthquakes as a complement to onshore observations. Key Points Propose a new method to estimate the near‐fault displacement waveform associated with an offshore earthquake Our method adopts the Kalman filter approach to combine the collocated strong‐motion seismometer and ocean‐bottom pressure gauge Since the obtained displacement waveforms have fault rupture information, it can improve the finite fault model