Shallow slow earthquakes have been documented along shallow plate interfaces near trenches. Recent geophysical observation networks located offshore of Japan enable us to analyze shallow tremors in the Nankai Trough and the Japan Trench. Onshore seismic stations are also important for detecting shallow very low frequency earthquakes (VLFEs) and for evaluating their seismicity prior to the deployment of offshore observation networks. This study analyzes data from ocean bottom seismometers to estimate the seismic energy radiation of such tremors, from which we observe along-strike heterogeneity. Tremors with higher seismic energy rates tend to have longer recurrence intervals, which has also been observed for deep tremors. This study also estimates seismic moment releases of shallow VLFEs at the Japan Trench observed by onshore seismic stations using Green's function in a local three-dimensional seismic velocity model. The scaled energy, which is the ratio of the seismic energy (rate) to the seismic moment (rate), is ~10⁻⁹. Shallow slow earthquakes located off the Kii Peninsula and Cape Muroto in the Nankai Trough have higher values (10⁻⁹–10⁻⁸), while shallow slow earthquakes located off the Kii channel in the Nankai Trough and in the Japan Trench have lower values (10⁻¹⁰–10⁻⁹), which are similar to the values estimated for deep slow earthquakes. By comparing the cumulative seismic energy of the shallow tremors with the cumulative seismic moment of shallow VLFEs, we evaluate the monitoring of shallow tremors and shallow VLFEs in the Japan Trench, suggesting that monitoring shallow VLFEs based on data from onshore seismic stations could miss many (~90% at most) of the seismic moment releases by small magnitude but frequent events.

沿沟槽附近的浅板界面记录了浅慢地震。位于日本海上的最新地球物理观测网络使我们能够分析南海海槽和日本海沟中的浅震。陆上地震台站对于检测浅层超低频地震（VLFE）和在部署海上观测网络之前评估其地震活动性也很重要。这项研究分析了来自海底地震仪的数据，以估算此类地震的地震能量辐射，从中我们观察到沿震带的非均质性。具有较高地震能级的地震往往具有较长的复发间隔，这在深部地震中也已观察到。这项研究还估计了日本海沟中浅层VLFE的地震矩释放，这些地震是在本地三维地震速度模型中使用格林函数通过陆上地震台站观测到的。标度能量约为10，是地震能量（比率）与地震矩（比率）之比^-9。位于南开海槽的纪伊半岛和室户角附近的浅慢地震的值较高（10 ^-9 –10 ^-8），而位于南开海槽和日本海沟的Kii通道附近的浅慢地震的值较低（ 10 ^-10 –10 ^-9），类似于深部慢地震的估计值。通过将浅地震的累积地震能量与浅VLFE的累积地震矩进行比较，我们评估了日本海沟中对浅地震和浅VLFE的监测，这表明基于陆上地震台站的数据来监测浅VLFE可能会错过很多（地震力矩的释放幅度很小，但频率很高，最多约90％。