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Fifty years since the first mobile phone call, the technology we carry
around in our pocket is helping to create the world's biggest earthquake
detection system.
O
On 25 October 2022, a 5.1-magnitude earthquake jolted California’s Bay
Area. Fortunately, it was more of a than a violent shake, but reports
from residents across the region flooded into the United States
Geological Survey (USGS) from those who had felt it. There was no damage
reported, but the earthquake was significant in another way – many
people in the area received alerts on their phones before the shaking
started.
More crucially still, many of these phones helped detect the earthquake
in the first place, too.
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Google has been working with USGS and academics at a number of
universities in California to develop an early warning system that
alerts users a few seconds before tremors arrive. It is a brief window
of warning, but a few seconds can give enough time to shelter under a
table or desk. It can also be enough time to slow trains, stop planes
from taking off or landing and keep cars from entering bridges or
tunnels. As such, this system is likely to save lives when stronger
quakes hit.
It uses data from two sources. Initially, the system relied upon a
network of the 700 seismometers – devices that detect earth tremors –
installed across the state by seismologists at USGS, the California
Institute of Technology and University of California Berkeley and the
state government. (Seismometers in two other US states – Oregon and
Washington – also feed into the system, known as ShakeAlert.) But Google
has also been creating what is the world's largest earthquake detection
network through phones owned by members of the public.
Most smartphones running Google's Android operating system have on-board
accelerometers – the circuitry which detects when a phone is being
moved. These are most commonly used to tell the phone to re-orientate
its display from portrait to landscape mode when it is tilted, for
example, and also helps provide information about step-count for
Google's onboard fitness tracker.
But the sensors are surprisingly sensitive, and can also act like a mini
seismometer.
Google has introduced a function that allows users to allow their phone
to automatically send data to the Android Earthquake Alerts System, if
their device picks up vibrations that are characteristic of the Primary
(P) waves of an earthquake. By combining data from thousands or even
millions of other phones, the system can work out whether an earthquake
is happening and where. It can then send out alerts to phones in the
area where the seismic waves are likely to hit, giving an early warning.
And because radio signals travel faster than seismic waves, the alerts
can arrive before the shaking starts in areas away from the epicentre.
Marc Stogaitis, a software engineer at Android, put it like this: "We’re
essentially racing the speed of light (which is roughly the speed at
which signals from a phone travel) against the speed of an earthquake.
And lucky for us, the speed of light is much faster!"
As most of the data is crowdsourced, the technology opens up the
possibility of monitoring for earthquakes in areas where there aren't
extensive networks of expensive seismometers. It means raises the
possibility of providing earthquake alerts in even remote and poorer
regions of the world.
In October 2022, engineers at Google saw phones across the San Francisco
Bay Area light up with earthquake detection data as the seismic waves
travelled outwards from the epicentre.
The now system regularly picks up these shakes. Most recently, on the
afternoon of 4 April 2023, a magnitude 4.5 earthquake that occurred near
Tres Pinos, California was picked up by the ShakeAlert system,
triggering messages on the mobile phones of uses in the area.
Earthquakes are a common occurrence in California, which experiences up
to 100 small quakes a day. Most of these are too small to feel. However,
there are typically several larger earthquakes in California per year,
with around 15-20 above magnitude 4.0.
More widely, of the estimated 16 billion mobile phones in use around the
world, more than three billion run Android on them and the Earthquake
Alerts System is now available in more than 90 countries that are
particularly prone to earthquakes.
But the system has its limitations, particularly in remote areas where
there are few phone users and in quakes that happen offshore, where they
can trigger tsunamis. And while it can help issue alerts a few seconds
in advance, the science of predicting earthquakes before they happen
remains as elusive as ever. (Read more about how scientists are trying
to spot the early signs of these natural disasters.)
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