This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Large pedestrian crowds generate distinctive seismic signals depending on their collective behavior, according to a new study that includes data from Tokyo schools and outdoor gatherings in the United States and Israel. These seismic signals are strongest in the 1–2 hertz frequency band, which is consistent with human walking frequencies.
But energetic outdoor gatherings produce signals that are stronger and more dependent on crowd activity than everyday pedestrian traffic, Asaf Inbal of Tel Aviv University reports in Seismological Research Letters. Inbal analyzed data from the 2020 Black Lives Matter march in Troy, New York, which included approximately 11,000 people, and a 2021 pilgrimage in Meron, Israel, that included about 100,000 people. The 2021 pilgrimage was the site of a deadly crowd crush that killed 45 people.
The increased amplification and scaling observed for these two events "likely reflect the more energetic and synchronized nature of motion during protests, marches and pilgrimages," Inbal writes, such as marching, rhythmic jumping and chanting. "We found that crowds engaged in coordinated activity tend to generate stronger seismic signals than similarly sized crowds engaged in uncoordinated activity," he explained. "More surprisingly, the seismic amplitudes associated with coordinated activity increase more rapidly with crowd size," Inbal added.
"This suggests that seismic excitation does not depend simply on the number of people. The type of activity also matters, and its influence becomes increasingly significant for larger crowds." Inbal's previous work on microseismicity in noisy urban environments, to learn more about how seismic noise levels affect earthquake detection, led to his interest in pedestrian seismic noise. Earlier studies, such as the well-known 2020 paper on the "seismic quiet" that fell over the world during COVID-19 lockdowns, demonstrate how human seismic noise levels rise and fall over long periods.
"However, relatively few studies have examined hourly variations. This motivated me to examine the Tokyo MeSO-Net data set, where I found a strong influence of school activity on seismic noise levels," Inbal said. The dense network of roughly 300 accelerometers installed as part of MeSO-Net is mostly located in Tokyo schoolyards, allowing Inbal to characterize the seismic signals of human activity during school hours.
The Tokyo observations "led me to consider whether seismic data could be used to characterize ground motion generated by human crowds more broadly," he said. Inbal used data from the Crowd Counting Consortium catalog, a public resource that collects data on political protest movements, to develop the ground-motion scaling relationships he used in his study. Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly.
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