Yabe Suguru, Nishida Kiwamu, Sakai Shinichi
Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567 Japan.
Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan.
Earth Planets Space. 2022;74(1):123. doi: 10.1186/s40623-022-01686-3. Epub 2022 Aug 9.
We conducted temporary seismic observations at the Hitachi-Kashiwa Soccer Stadium on a J. LEAGUE game day to obtain unique seismic records due to the collective action (i.e., jumping) of supporters, which were also recorded in a permanent Metropolitan Seismic Observation network (MeSO-net) station. This study investigated seismic wave excitation as well as seismic wave propagation from the stadium to its surroundings. The rhythms of the jumps of the supporters were characterized by analyzing audio data recorded in the stadium, which were compared with the characteristic frequencies observed in the seismic records. The characteristic frequencies in the seismic records are integer multiples of the jumping rhythms, which is consistent with the loading model of jumping people proposed in earlier studies. This implies that seismometers could be useful for monitoring collective human activity. Travel times were studied using deconvolved waveforms because seismic waves generated by the supporters are sinusoidal with vague onset. Polarization analysis was performed to measure the amplitude and polarization azimuths. The observed seismic wave propagation was compared with synthetic waveforms calculated using one-dimensional physical properties based on the Japan Seismic Hazard Information Station (J-SHIS). The synthetic waveforms calculated with the shallow and deep layer combined model are more consistent with observations of travel times and amplitude decay than those calculated with the only deep layer model, although a part of the observations cannot be explained by both models. This result suggests that the subsurface structure of J-SHIS is good in this region, although a more detailed three-dimensional structure and topography must be considered to fully explain the observations. As human-induced seismic signals are expected to be generated in various situations, this study shows that such unique seismic waves can be used as an artificial seismic source for validating and improving local shallow subsurface structural models in urban environments.
我们在日立柏足球场的一场日本职业足球联赛比赛日进行了临时地震观测，以获取由于观众集体行动（即跳跃）产生的独特地震记录，这些记录也被一个永久性的东京都地震观测网络（MeSO-net）台站记录下来。本研究调查了地震波的激发以及从体育场到其周边地区的地震波传播情况。通过分析体育场内录制的音频数据来表征观众跳跃的节奏，并将其与地震记录中观测到的特征频率进行比较。地震记录中的特征频率是跳跃节奏的整数倍，这与早期研究中提出的人群跳跃加载模型一致。这意味着地震仪可用于监测集体人类活动。由于观众产生的地震波是正弦波且起始模糊，因此使用反褶积波形研究了走时。进行了极化分析以测量振幅和极化方位角。将观测到的地震波传播与基于日本地震灾害信息站（J-SHIS）使用一维物理性质计算的合成波形进行了比较。与仅使用深层模型计算的合成波形相比，使用浅层和深层组合模型计算的合成波形在走时和振幅衰减观测方面与观测结果更一致，尽管部分观测结果无法用这两种模型解释。这一结果表明J-SHIS的地下结构在该区域是良好的，尽管必须考虑更详细的三维结构和地形才能充分解释观测结果。由于预计在各种情况下都会产生人为诱发的地震信号，本研究表明，这种独特的地震波可作为人工地震源，用于验证和改进城市环境中的局部浅层地下结构模型。
