Earthquakes & Liquefaction
Earthquakes
An earthquake is what happens when two blocks of the earth suddenly slip past one another, along fault lines. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter. Sometimes an earthquake has foreshocks, smaller earthquakes that happen in the same place as the larger earthquake that follows. The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock.1 Earthquakes are measured by the Richter Magnitude Scale, ranging from 1 to 10 in Magnitude of intensity of ground shaking.
Soil Liquefaction
Liquefaction occurs when loosely packed, water-logged sediments (soil) near the ground surface lose their strength in response to strong ground shaking. Liquefaction occurring beneath buildings and other structures can cause major damage during earthquakes, because the soil vibrates and acts similar to quicksand.
Earthquake Facts
- Earthquakes strike suddenly, violently and without warning at any time of the year and at any time of the day/night.
- Smaller earthquakes often follow the main shock.
- Ground shaking from earthquakes can collapse buildings and bridges; disrupt gas, electric and phone service and, sometimes, trigger landslides, avalanches, flash floods, fires and huge, destructive ocean waves (tsunamis).
- Most earthquake-related injuries result from collapsing walls, flying glass and falling objects.2
Earthquake Safety Tips
- Drop, Cover and Hold. Most injuries during earthquakes occur because of tripping and suffering sprains / fractures and head injuries from falling debris.
- If you are in bed, stay there, curl up and hold on, and cover your head.
- Stay indoors until the shaking stops and you are sure it is safe to exit.
- Be aware that smoke alarms and sprinkler systems frequently go off in buildings during an earthquake, even if there is no fire.
- If you smell gas, get out of the building and move as far away as possible.
- If you are outdoors, find a clear spot and drop to the ground, avoid buildings, power lines, trees, and streetlights as possible.
- If you're in a vehicle, pull over to a clear location and stop. Avoid bridges, overpasses and power lines if possible. After the shaking has stopped, drive on carefully, avoiding bridges and ramps that may have been damaged.
- If a power line falls on your vehicle, do not get out. Wait for assistance.3
For more information about earthquakes and liquefaction, visit:
1 Source: https://www.usgs.gov/natural-hazards/earthquake-hazards/science/science-earthquakes?qt-science_center_objects=0#qt-science_center_objects
2 Source: https://www.fema.gov/earthquake-fast-facts
3 Source: https://www.redcross.org/get-help/how-to-prepare-for-emergencies/types-of-emergencies/earthquake.html
