It was almost midnight last Tuesday when Mexico City's seismic alert woke up Carmina Robles.
The 76-year-old said she jumped out of bed and made for the nearest weight-bearing column, hoping it would provide protection when the earthquake struck. The minutes passed and nothing moved so she went back to bed.
"I said to myself: 'Oh God, please don't let it be like the one in 1985,'" Robles recalled the anxiety she felt at first. "I got scared, but thankfully nothing happened."
About 12 hours later the sirens wailed again, prompting the evacuation of schools, offices and public buildings across the city. This time some residents did report feeling a mild tremor.
Many residents still remember the 8.5 magnitude quake of 1985 that killed 12,843 people, according to official figures. Fear of a repeat is seen in the way phone lines can crash from people calling round to check up on relatives and friends after they feel a tremor, even when there is no obvious sign of damage.
But the activation of the capital's dramatically expanded early warning alert this week to prepare people for two barely perceptible tremors has raised questions about whether the technology is being overused, and concerns it is provoking unnecessary panic or perhaps even alert fatigue.
"The early warning system has proven to be useful and effective," Armando Cuellar Martínez, of the Mexican office in charge of the alert told VICE News. "It gives people time to prepare."
But while Cuellar complained about a "lack of education on earthquakes that needs to be taken care of," he also acknowledged that the wider dissemination of the alert in recent years calls for new parameters for deciding when it should be activated.
The epicenters of the earthquakes Mexico City residents worry about tend to be hundreds of miles away along the Pacific coast, rooted in movements of the Cocos and North American tectonic plates. The city's vulnerability even to these resides in its location on top of a dried out lake bed where the water-clogged ground amplifies the impact of the earthquake's energy once it arrives.
The distance from the actual site of the energy release, however, gives the Mexican capital the life-saving possibility of an early warning system that can give residents up to two minutes to prepare themselves before the shaking starts. Japan is one of the few other countries where similar early-warning systems exist.
The Mexican system, set up in 1991, relies on sensors monitoring seismic activity along the Pacific coastline through the states of Jalisco, Colima, Oaxaca, northern Guerrero, and Colima. The sensors activate the alarms when they pick up a tremor above 5 on the Richter Scale.
In previous decades the alert was only broadcast on the radio, in the metro, government buildings and state sector schools.
In recent years, however, the alarms have got more personal, regularly sounding out through smartphone apps that have sometimes been wrongly activated.
This year Mexico City has also expanded the number of street speakers emitting the alarm from 1,800 to 8,200.
Some say the sirens set off this week – the first for a tremor with a magnitude of 4.6 that the sensors initially logged as over 5, and the second with a magnitude of 5.5 – are causing unnecessary fear and disruption.
"When you hear the alarm you get scared because of how loud it it is," Lucia Hernández, a 26-year-old shopkeeper said. "Then nothing happens, and you are left unnecessarily panicked."
And while some panic, others now barely pay attention.
College student Gabriela Garay told VICE News that she only believes an earthquake is taking place if she feels it.
"Whenever I hear the alert, I ignore it," she said.
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