Coordinated activity gives large pedestrian crowds a distinctive seismic signature

This research reveals that large pedestrian crowds produce distinctive seismic signals, which are particularly strong in the 1–2 hertz frequency range. These signals align with the typical walking frequencies of humans. However, energetic outdoor gatherings featuring coordinated activity generate even stronger and more crowd-dependent seismic signals compared to everyday pedestrian traffic.

Asaf Inbal of Tel Aviv University conducted a study analyzing data from the 2020 Black Lives Matter march in Troy, New York, which involved around 11,000 participants, and a 2021 pilgrimage in Meron, Israel, attended by approximately 100,000 people. The 2021 pilgrimage tragically led to a crowd crush that resulted in 45 fatalities.

Inbal's findings suggest that the intensity of seismic signals is amplified more significantly and scales more rapidly with the size and nature of the crowd. This amplified response seems to be a result of coordinated activities like marching, rhythmic jumping, and chanting, which set these gatherings apart from uncoordinated crowds.

What makes these findings intriguing is that the seismic amplitudes associated with coordinated activities increase more swiftly as the crowd size grows. This indicates that crowd size alone does not determine seismic excitation; rather, the type of activity also plays a critical role, becoming even more influential among larger groups.

Earlier research, including a notable 2020 study on reduced seismic noise levels during COVID-19 lockdowns, demonstrates how human-generated seismic noise fluctuates over time, but fewer studies have focused on short-term, hourly variations. Inbal's exploration into Tokyo's MeSO-Net data set, comprised of roughly 300 accelerometers primarily located in schoolyards, allowed him to detect the seismic signals originating from school activities.

By leveraging data from the Crowd Counting Consortium, a public resource cataloging political protest movements, Inbal constructed scaling relationships that link ground motion to crowd behavior. He refers to these relationships as "People's Magnitude," emphasizing that the seismic signals are not solely influenced by the number of people present but also by how they move and coordinate.

Inbal's research draws parallels with studies on collective crowd behavior conducted by physicists, both of which highlight the potential collective impact of human interactions on their surroundings.