Seismic Alert: why it sometimes sounds like low-intensity tremors

The Mexican Seismic Warning System is scheduled to use speakers for telluric movements above 6 degrees on the Richter scale

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CIUDAD DE MÉXICO, 19SEPTIEMBRE2021.- Las
CIUDAD DE MÉXICO, 19SEPTIEMBRE2021.- Las personas que andaban en bicicleta detuvieron su marcha al escuchar la alarma sísmica en punto de las 11:30 sobre Paseo de la Reforma, a la altura del Ángel de la Independencia, por el simulacro con hipótesis de temblor que convocó Protección Civil, en el marco de la conmemoración de los sismos de 1985 y 2017, ambos ocurridos un 19 de septiembre. FOTO: MOISÉS PABLO/CUARTOSCURO.COM

Mexico City and several states in the country were again surprised with the preventive warning of the Mexican Seismic Warning System (SASMEX), so thousands of citizens evacuated their homes or work in order to safeguard themselves in the event of an accident.

This system works by evaluating three algorithms that boast “high reliability” to determine their possible magnitude. This is equated in more than two Sasmex stations throughout Mexico and immediately determines a projection of intensity on a Richter scale.

If it exceeds 6 Richter degrees, the alerts distributed in Mexico will be triggered to prevent citizens from the earthquake reaching their entity; however, this system is not accurate at first and on several occasions the Seismic Alert is triggered by low-intensity telluric movements.

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People left their homes and offices when they heard the seismic alarm in CDMX, however, citizens said they didn't feel any movement (Photo: Karina Hernández/Infobae)

Why is the seismic alert triggered for low intensity tremors?

In summary, the Sasmex algorithm that projects the intensity estimates that rarely corresponds to the official magnitude, so as a prevention it activates alerts if they are close to 6 degrees of the Richter scale, with a high margin of error due to immediacy.

*Information in development