We analyzed strong-motion records at the ground and borehole in and around the Kanto Basin and the seafloor in the Japan Trench area from three nearby offshore earthquakes of similar magnitudes (Mw 5.8-5.9). The seafloor strong-motion records were obtained from S-net, which was established to enhance tsunami and earthquake early warnings after the 2011 great Tohoku-oki earthquake disaster. The borehole records were obtained from MeSO-net, a dense network of seismometers installed at a depth of 20 m in the Tokyo metropolitan area. The ground records were obtained from the K-NET and KiK-net networks, established after the 1995 great Hanshin-Awaji earthquake disaster. The MeSO-net and S-net stations record the shakings continuously, while the K-NET and KiK-net records are based on triggering thresholds. It is crucial to evaluate the properties of strong motions recorded by the S-net for earthquake early warning (EEW). This paper compared the peak ground accelerations (PGAs) and peak ground velocities (PGVs) between the S-net and K-NET/KiK-net stations. Because the MeSO-net records were from the borehole, we compared the PGAs and significant durations of the low-frequency motions (0.1 to 0.5 Hz) between the S-net and MeSO-net stations from identical record lengths. We found that the horizontal PGAs and PGVs at the S-net sites were similar to or larger than the K-NET/KiK-net sites for the S wave. In contrast, the vertical PGAs and PGVs at the S-net sites were similar to or smaller than those at the K-NET/KiK-net sites for the S wave. Particularly, the PGAs and PGVs for the P-wave parts on the vertical-component records of S-net were, on average, much smaller than those of K-NET/KiK-net records. The difference was more evident in the PGAs. The average ratios of S-wave horizontal to vertical PGAs were about 2.5 and 5 for the land and S-net sites, respectively. The low-frequency PGAs at the S-net sites were similar to or larger than those of the MeSO-net borehole records. The significant durations between the two-networks low-frequency records were generally comparable. Quantification of the results from a larger dataset may contribute to ground-motion prediction for EEW and the design of the offshore facilities.

中文翻译：

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关东盆地附近S-net海底地震台站地震预警强震参数评价

我们分析了附近发生的三场类似震级（Mw 5.8-5.9）的近海地震中关东盆地及其周围的地面和钻孔以及日本海沟地区海底的强震记录。海底强震记录来自S-net，S-net是为了在2011年东北大地震后加强海啸和地震预警而建立的。钻孔记录是从 MeSO-net 获得的，MeSO-net 是一个密集的地震仪网络，安装在东京都市区 20 m 的深度。地面记录来自 K-NET 和 KiK-net 网络，这些网络是在 1995 年阪神-淡路大地震灾难后建立的。MeSO-net 和 S-net 站连续记录震动，而 K-NET 和 KiK-net 记录基于触发阈值。评估 S-net 记录的强震特性对于地震预警 (EEW) 至关重要。本文比较了 S-net 和 K-NET/KiK-net 站之间的峰值地面加速度 (PGA) 和峰值地面速度 (PGV)。由于 MeSO-net 记录来自钻孔，因此我们比较了相同记录长度的 S-net 和 MeSO-net 台站之间的 PG​​A 和低频运动的显着持续时间（0.1 至 0.5 Hz）。我们发现 S-net 站点的水平 PGA 和 PGV 与 S 波的 K-NET/KiK-net 站点相似或更大。相比之下，S 网站点的垂直 PGA 和 PGV 与 S 波的 K-NET/KiK-net 站点的垂直 PGA 和 PGV 相似或更小。特别是，S-net 垂直分量记录上 P 波部分的 PGA 和 PGV 平均为，远小于 K-NET/KiK-net 记录的记录。这种差异在 PGA 中更为明显。对于陆地和 S-net 站点，S 波水平与垂直 PGA 的平均比率分别约为 2.5 和 5。S-net 站点的低频 PGA 与 MeSO-net 钻孔记录相似或更大。两个网络低频记录之间的显着持续时间通常具有可比性。对来自更大数据集的结果进行量化可能有助于 EEW 的地面运动预测和海上设施的设计。S-net 站点的低频 PGA 与 MeSO-net 钻孔记录相似或更大。两个网络低频记录之间的显着持续时间通常具有可比性。对来自更大数据集的结果进行量化可能有助于 EEW 的地面运动预测和海上设施的设计。S-net 站点的低频 PGA 与 MeSO-net 钻孔记录相似或更大。两个网络低频记录之间的显着持续时间通常具有可比性。对来自更大数据集的结果进行量化可能有助于 EEW 的地面运动预测和海上设施的设计。