It’s impossible to predict when an earthquake will happen. The patterns of migrating birds, abnormally sharp air pressure drops, the tone of goat vocalizations — none of these things actually signal an abrupt shift in the crust of our planet (though dark corners of the Internet may claim they do).

So without warning, entire cities — or in the case of Haiti, entire countries — can be leveled. The only sign an earthquake is about to strike is the ground itself starts to move.

However, before the initial lurch and even well-before the walls start to buckle, there are invisible waves moving through the ground only detected by seismometers. These first waves don't do any damage, but they serve as a clear signal that something worse is coming. With a dense network of sensors in the ground, you can take advantage of the early waves to send a warning downstream.

ShakeAlert — the U. S. Geological Survey’s early warning system — is made of an array of individual seismic stations located throughout the West Coast.

Seattle

WASHINGTON

Historically

active

faults

Portland

OREGON

IDAHO

NEVADA

San Francisco

Seismic

sensor

station

CALIFORNIA

Las

Vegas

Los Angeles

ARIZ.

Transmitter

Battery and

solar array

Cover

Datalogger

Vibrations

from

earthquake

Seismic

sensor

ShakeAlert — the U. S. Geological Survey’s early warning system — is made of an array of individual seismic stations located throughout the West Coast.

Seattle

WASHINGTON

Historically

active

faults

Portland

OREGON

IDAHO

NEVADA

Transmitter

San Francisco

Seismic

sensor

station

CALIFORNIA

Las

Vegas

Los Angeles

Battery and

solar array

ARIZ.

Cover

A datalogger

records and

sends digital

seismic data

through a

transmitter

Vibrations

from

earthquake

A seismic

sensor

detects

vibrations

ShakeAlert — the U. S. Geological Survey’s early warning system — is made of an array of individual seismic stations located throughout the West Coast.

Transmitter

Seattle

WASHINGTON

Battery and

solar array

Portland

Historically

active

faults

OREGON

IDAHO

Cover

NEVADA

A datalogger

records and

sends digital

seismic data

through a

transmitter

San Francisco

Seismic

sensor

station

CALIFORNIA

Las Vegas

Vibrations from

earthquake

Los Angeles

ARIZ.

A seismic

sensor

detects

vibrations

Transmitter

ShakeAlert — the U. S. Geological Survey’s early warning system — is made of an array of individual seismic stations located throughout the West Coast.

Seattle

WASHINGTON

Historically

active

faults

Battery and

solar array

Portland

OREGON

IDAHO

Cover

NEVADA

San Francisco

Seismic

sensor

station

A datalogger

records and

sends digital

seismic data

through a

transmitter

CALIFORNIA

Las Vegas

Vibrations from

earthquake

Los Angeles

ARIZONA

A seismic

sensor

detects

vibrations

Technological speed is the only reason earthquake warnings became possible, and with improvements to the warning technology, they could arrive even faster.

After a catastrophic loss of life in the 8.0-magnitude 1985 earthquake, Mexico launched a warning system that alerted people up to a minute in advance of the Sept. 7 quake. It also gave people in Mexico City 10 to 15 seconds to prepare for the deadly earthquake that struck Sept. 19 -- a shorter lead time due to how close the epicenter was to the capital.

This is what the U.S. Geological Survey, the California governor’s office, and research groups across the West are on their way to accomplishing with ShakeAlert.

To understand seismic waves, imagine that the ground is liquid. In practice this may not make sense, but physically it's entirely legitimate. Dirt, rocks, sediment — all of the things that make up the Earth beneath our feet — are just fluids with a very (very) high density.

Waves move across the ground just like they move across the ocean. It might be helpful to think of them like sound waves in air — when thunder cracks, we know the sound waves exist because we can hear them, but they also rattle the windows and shelves around us. They are literally pushing and pulling the air as they travel through it.

Populated

area

Epicenter

Fault

An earthquake happens when one section of Earth abruptly slips past another along a fault.

Epicenter

Populated

area

Fault

An earthquake happens when one section of Earth abruptly slips past another along a fault.

Epicenter

Populated

area

Fault

An earthquake happens when one section of Earth abruptly slips past another along a fault.

Epicenter

Populated

area

Fault

An earthquake happens when one section of Earth abruptly slips past another along a fault.

Seismic waves come in a few different flavors. Primary waves do little damage and they may be imperceptible, but they “announce” the arrival of the slow surface waves, which jostle everything above ground.

Faster, less damaging

primary waves

Sensors at seismic

stations detect primary waves.

Faster, less damaging primary waves

Sensors at seismic

stations detect primary waves.

Faster, less damaging primary waves

Sensors at seismic

stations detect primary waves.

Faster, less damaging primary waves

Sensors at seismic

stations detect primary waves.

Primary waves come first and fast. They do little damage, but they “announce” the arrival of the secondary waves, which cause the intense shaking.

At the moment of rupture, primary waves careen away from the epicenter like a spring. Imagine laying a slinky on the floor and stretching it out, then letting it go. The pushing-pulling waves you see in the slinky are exactly what's happening in the Earth as the primary wave rolls under your feet.

Alert warning

Data are transmitted immediately to alert centers, analyzed and broadcast as a warning.

Alert warning

Data are transmitted immediately to alert centers, analyzed and broadcast as a warning.

Alert warning

Data are transmitted immediately to alert centers, analyzed and broadcast as a warning.

Alert warning

Data are transmitted immediately to alert centers, analyzed and broadcast as a warning.

The secondary and surface waves do the damage. They’re slower and they come after the primary waves. Take your slinky and give it a quick upward jolt and you can see these waves in action. This is what the network is warning for — the kind of waves that make the ground look like ocean swells.

Populated area

Slower, more damaging

secondary waves

Populated

area

Slower, more damaging secondary waves

Slower, more damaging secondary waves

Populated

area

Slower, more damaging secondary waves

Populated

area

When the early warning system detects the primary wave, the digital information is sent almost instantaneously — much faster than the damaging waves — so people are given seconds to minutes to prepare.

Every second matters

Once you get the warning, you can take action. You can leave your house, move away from structures or, at the very least, dive under your desk. Factories and plants can shut down operations to prevent loss and damage — and get workers to safety. Though it might not sound like a lot, even a few seconds of advance notice can be important before strong shaking occurs.

Stop vehicles, find cover

and hold on

Move personnel and school children to safe locations

Stopping surgeries and other delicate procedures

Emergency responders can open garage doors and prepare

Stop trains, stop elevators on next floor

Shut off gas lines and protect power grid

Stop vehicles, find

cover

and

hold on

Move personnel and school children

to safe locations

Stopping surgeries and other delicate procedures

Emergency responders can open garage doors and prepare

Stop

trains,

stop elevators on next floor

Shut off gas lines and protect power grid

Stop vehicles, find

cover

and

hold on

Move personnel and school children

to safe locations

Stopping surgeries and other delicate procedures

Emergency responders can open garage doors and prepare

Stop

trains,

stop elevators on next floor

Shut off gas lines and protect power grid

Even in its experimental phase, ShakeAlert has already proved invaluable.

BART — the San Francisco Bay Area's rapid transit system — has used the warnings since 2012 to slow down trains and prevent derailment. The system proved successful in 2014 in the 6.0-magnitude earthquake in Napa, Ca., though the shaker occurred overnight when trains weren't running. A BART representative said the system got the alert as intended.

In 2015, a 4.0 earthquake in Oakland triggered the alert, and BART slowed trains as a result.

The 1906 San Francisco earthquake devastated much of Northern California. Even cities far from the epicenter were hit hard with no warning. If a similar quake were to strike again, an early warning system would give people time to take cover.

50 MILES

Eureka

Over a minute

CALIFORNIA

101

5

80

Sacramento

Napa

10 seconds

Berkeley

No warning

San Francisco

No warning

San Jose

15 seconds

1906 EARTHQUAKE

EPICENTER

Salinas

35 seconds

5

Weaverville

Eureka

Over a minute

Redding

Weott

Chester

Garberville

Red Bluff

101

Portola

Chico

CALIFORNIA

Fort Bragg

5

Williams

Yuba City

80

Cloverdale

Sacramento

Santa Rosa

Napa

10 seconds

Petaluma

Berkeley

No warning

Stockton

San Francisco

No warning

Oakland

Modesto

Fremont

1906 EARTHQUAKE

EPICENTER

Merced

San Jose

15 seconds

Santa Cruz

5

Salinas

35 seconds

50 MILES

Weaverville

Eureka

Over a minute

Redding

Weott

Chester

Garberville

Red Bluff

5

Chico

101

Portola

CALIFORNIA

Fort Bragg

Williams

Yuba City

80

Cloverdale

Sacramento

Napa

10 seconds

Santa Rosa

Petaluma

Berkeley

No warning

Stockton

San Francisco

No warning

Oakland

Modesto

Fremont

1906

EARTHQUAKE

EPICENTER

Merced

San Jose

15 seconds

Santa Cruz

Salinas

35 seconds

5

50 MILES

It began sending test notifications to selected users in California in January 2012. But hundreds of sensors still need to be installed -- something Gov. Jerry Brown and the California state legislature partially funded in 2016 -- and still, once that happens, the system would not be capable of sending alerts via cellular networks.

Quite simply, the cell phone network isn’t fast enough for earthquakes, says Doug Given, the Earthquake Early Warning Coordinator at USGS.

“The Wireless Emergency Alerts system was designed years ago, without consideration for speed,” Given told The Washington Post. “And there are no regulatory requirements about the speed of delivery.”

With just seconds to take cover before an earthquake strikes, the network needs to be lightning fast. It’s not there yet.

Japan already has an early warning system, which automatically alerts cellphones, TV crawlers and radio. Officials have called that system a success, though disasters like the 2011 tsunami couldn't be prevented with seismic warning.

Mexico, China, Taiwan, Korea and Turkey all have early warning systems -- all motivated by major earthquake disasters. Given hopes it won’t take a major loss of life in the U.S. to bring the ShakeAlert system to fully-functional.

“We’re trying to be the counterexample,” he said.

About this story

ShakeAlert is an earthquake early warning system developed by the U.S. Geological Survey along with a coalition of state and university institutions.

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