A magnitude 5.6 [1] earthquake shook Mexico City on June 5, 2024 [2], but the public seismic alert system did not sound.
The failure of the sirens during a perceptible tremor raises concerns about the reliability of early warning systems in one of the world's most seismically active urban areas.
Miriam Urzúa, a spokesperson for Protección Civil, said the initial seismic energy was insufficient to trigger the system [3]. Additionally, the epicenter of the quake was located beyond the specific distance threshold required to activate the city's sirens [3].
While the tremor was felt by residents, officials reported no damages [1]. The discrepancy between the felt experience and the lack of an alarm has led to public questioning of the system's parameters.
Some reports suggested that specific alert posts, such as those identified as MI C911, do not emit the seismic alert [4]. This technical limitation may contribute to why some residents did not hear the warning even if the system had partially activated.
Protección Civil said the system functioned according to its design. The sirens are programmed to activate only when specific energy, and distance criteria are met to avoid false alarms or unnecessary panic during minor events [3].
“The initial seismic energy was insufficient and the epicenter was beyond the distance threshold.”
This incident highlights the technical gap between a 'felt' earthquake and a 'trigger' earthquake. Because seismic alert systems rely on specific thresholds of energy and distance to prevent mass panic from low-risk tremors, residents may experience shaking without warning. This creates a psychological challenge for public safety officials who must balance the need for caution with the risk of system desensitization.
