Pedestrian crowds shake the ground in ways scientists can now tease apart. Writing in Seismological Research Letters, researcher Asaf Inbal at Tel Aviv University shows human footfall peaks near one to two hertz — walking pace — yet synchronised motion packs a louder punch than everyday traffic of similar size. Marches, protests and pilgrimages amplify and climb faster with headcount than ordinary city bustle.
His examples include roughly eleven thousand people at a 2020 justice march in Troy, New York, and about one hundred thousand pilgrims at Meron, Israel, in 2021, a gathering later scarred by a fatal crush. Shared stepping, jumping and chanting, the paper argues, help explain the stronger excitation. Inbal half-jokingly labels the scaling a “People’s Magnitude”: metrics that track how bodies move, not only how many gather.
Curiosity began with Tokyo’s MeSO-Net — around three hundred accelerometers, many planted in schoolyards — where daily classroom rhythms leapt out of the noise. That hourly pattern pushed him to ask whether seismic archives could describe crowds more generally. Protest tallies compiled by the Crowd Counting Consortium then helped relate event size to ground motion across cases.
Borrowing ideas from physicists who study collective motion, he wonders whether a changing seismic fingerprint might flag behavioural shifts before cameras or manual counts do — useful for safety and urban science. The article stops short of saying seismometers replace policing; it argues they add an independent, physics-based lens on mass gatherings. Whether agencies ever adopt the method operationally is unsettled — as basic research, though, the study already shows crowds can be told apart by physics alone.
