What would you do if you have seconds to prepare for
shaking from an earthquake that has already begun?
More than 143 million people in the united states
are exposed to potentially damaging shaking due to earthquakes.
Most of our nation's earthquake risk is concentrated in highly populated areas
on the active plate tectonic boundaries of the west coast of the continental
united states. The U.S geological survey operates the
ShakeAlert earthquake early warning system
which is part of the advanced national seismic system.
ShakeAlert is not earthquake prediction but a shake alert message issued by the
USGS indicates that an earthquake has begun and shaking is imminent.
[Teacher "....don't let yourself be convinced to do something
that you know is bad and then again..."]
With even a few seconds of warning ShakeAlert can save lives and reduce
injuries by alerting people to take a protective action, such as DROP
COVER and HOLD ON. ShakeAlert further protects people and infrastructure
by triggering automatic actions such as
slowing down trains to prevent derailments, opening firehouse doors so they don't
jam shut, and closing valves to protect water systems
and to stabilize equipment during life critical situations.
How does shake alert work?
When an earthquake occurs
seismic waves carry energy in all directions away from the epicenter.
P waves, similar to sound waves, move quickly through the ground
followed by the slower and generally more damaging S waves and surface waves.
Sensors detect the seismic waves and send that information to a ShakeAlert
processing center which requires that at least four sensors detect the earthquake.
If the earthquake fits the right profile, the USGS
issues a ShakeAlert message. Distribution partners then produce and
deliver an alert to people, and trigger automated systems.
Alert delivery can be before during or after shaking
from s waves and surface waves. Alerts can be delivered to people through apps
designed for cell phones and other wireless devices,
over public address systems, tvs and radios,
and by fema's wireless emergency alert system WEA.
which is also the source of amber alerts. Dor every earthquake there is a region
near the epicenter where alerts will not arrive before
shaking begins. That's because close to the epicenter
the P and S waves are too close together and the ShakeAlert ystem needs time,
often just seconds, to estimate the earthquake's magnitude and shaking
levels before issuing a ShakeAlert message.
That means that people close to the earthquake epicenter
might not get an alert until after the shaking has already started.
those farther away from the epicenter could receive more warning time before
shaking arrives. If an earthquake continues to grow in
size, additional ShakeAlert messages might be issued.
Updating the estimated magnitude and expected shaking for that event
will result in alerts being delivered to a broader area.
The USGS recommends that when you receive an alert
you should take protective action immediately. Do not wait for shaking to arrive.
If you are near the coast in a tsunami prone region
it's important to get to high ground quickly but only after shaking stops.
Before traveling to a new place
learn about both the local hazards and the recommended precautions to take
by reading information found in the city county or state's
emergency management websites. Knowledge of your surroundings and
practicing protective actions are critical components of
preparedness for any disaster, Always remember: if you receive an
earthquake alert, or experience shaking DROP, COVER
and HOLD ON until all shaking stops