Did the Android alert really anticipate the earthquake in Venezuela?

In the last few hours there have been many comments on the nature of this notification, but cAs specified by the seismologist Alessandro Amato in an in-depth study for INGVterremoti, the statement according to which the telephones would have anticipated the phenomenon is not scientifically accurate, since the citizens received the alert after the earthquake had already occurred or, to be precise, when the tremor had already begun.

The rupture process of a fault as large as the one that was activated in Venezuela, about 200 kilometers long, in fact lasts a few tens of seconds and, while the fracture propagates emitting energy in the form of seismic waves, the areas closest to the hypocenter undergo an immediate shaking. The monitoring technology is not based on predicting earthquakes, a possibility ruled out by modern science, but exploits the fact that the first waves produced, the P waves, are faster and less destructive than the subsequent shear or jolt waves, called S waves.

The difference in arrival times between the two wave fronts increases with the distance from the epicenter, offering a margin that at 50 kilometers can be 10-15 seconds, but which unfortunately disappears almost completely for those who are directly above the epicentral area. By having instruments capable of measuring the motion of the ground, it is possible to quickly estimate the intensity of the ongoing shaking to predict its impact on the surrounding areas, a key principle of early warning systems known as Earthquake Early Warning System which exploits digital signal transmission at the speed of light, far exceeding the speed of propagation of telluric waves.

This mechanism follows that of tsunami warnings, where however the marine propagation times measurable in minutes or hours allow significantly higher safety margins for informing coastal populations. In the specific case of Venezuela, the Android Earthquake Alerts system developed by Google with the scientific support of the University of Berkeley’s seismological laboratory and its main creator Richard Allen, did not use a traditional seismic network, but quickly and massively analyzed the data coming from the tiny accelerometers integrated into mobile devices.

Although such home sensors do not guarantee the high quality of professional scientific instruments, their strength lies in their numerical capillarity, given that compared to a few hundred or thousands of official seismometers present even in the most monitored regions such as Japan, California or Italy, millions of active smartphones exist in the same territory. The success of the alert last June 24 was also favored by the peculiar geological evolution of the event, characterized by two strong tremors in rapid succession.

As told by Alessandro Amato in the in-depth article, data from the US agency USGS indicate a first event of magnitude 7.2 at 22:04:33 UTC and a second episode of magnitude 7.5 which occurred just 39 seconds later. Since the duration of the fault rupture for the first earthquake was quantifiable in a few tens of seconds, the second and more powerful shock began when the previous one was still in progress or had just ended, prompting researchers from the National Institute of Geophysics and Volcanology to hypothesize a single complex rupture process, with two main energy release zones along the same tectonic structure.

Image credits INGV

The analyzes carried out on satellite and seismological data indicate that the fault has propagated from West to East, moving precisely in the direction of Caracas and worsening the overall impact on the capital. The entire process of generating waves on the surface of the fault lasted about a minute and a half, although the perception of the shaking by the population lasted much longer due to the phenomena of reflection and refraction of the waves within the earth’s crust. Google’s alert reached distant areas such as the island of Curacao, about 300 kilometers from the epicentre, however estimating a magnitude of 6.2, a value significantly underestimated compared to the real data and about 90 times lower than the energy actually released by the 7.5 magnitude earthquake.

A few seconds can still make the difference in allowing people to move away from windows and heavy objects, or in preparing themselves psychologically by reducing the panic effectas demonstrated by various sociological studies also conducted in Italy. The Italian territorycharacterized by a high seismic risk, has been experimenting with early warning systems for some time, although a historical mistrust remains linked to the fact that earthquakes on the peninsula generally present smaller magnitudes and shorter faults than those of Venezuela or Turkey, concentrating the main damage within a few kilometers from the epicenter, right inside the so-called “blind zone”.

Nonetheless, technological progress in data transmission has made it possible to implement innovative solutions, such as the early warning system applied by the Italian Railway Network and the University of Naples on the Rome-Naples high-speed route, while the INGV has started experiments for a national warning network, a sector in which Google’s technology is not currently operational.

Lto protect human life, as Alessandro Amato’s analysis concludes, cannot in any case rely exclusively on the timeliness of a notification on a mobile screensince a ten or twenty second warning does not offer the material time to abandon a building, but only allows you to take shelter under solid structures such as tables or benches. The real reduction of seismic risk therefore remains inextricably linked to the structural quality of the building stock and to systematic anti-seismic adaptation interventionsparticularly in the most dangerous areas of the country. In Venezuelan urban areas, the advance notification still gave many families time to reach safety.