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Aftershock

Earthquakes can cause primary and secondary hazards, some of which you can be prepared for. Building collapses and aftershocks are two of the most commonly known dangers. Utility line ruptures, fires, chemical leaks, liquefaction and landslides are just a few examples of additional hazards caused by major earthquakes. If a major earthquake occurs, you should be aware of these potential hazards as you look for help and begin recovering from the disaster.

Aftershocks are earthquakes that follow the largest shock of an earthquake sequence. They are usually smaller than the mainshock and within 1-2 rupture lengths distance from the mainshock. Aftershocks can continue over a period of weeks, months, or years. After the 1886 Summerville earthquake, 300 aftershocks were recorded in the Lowcountry for a 2 ½ year period. In general, the larger the mainshock, the larger and more numerous the aftershocks, and the longer they will continue.

Primary Effects

Primary Effects are features that are always present in a severe earthquake. When the earthquake is over, review what has occured.

  • Buildings collapse
  • Electric lines and gas mains can snap
  • Large areas of ground can shift position
  • Large bodies of water can rise and fall

Secondary Effects

Secondary effects are other disasters caused by the ground movement of earthquakes. Most of the damage done by earthquakes is due to secondary effects that can occur over very large regions, causing wide-spread damage, such as:

Landslides
These occur in hilly/mountainous regions. The damage caused can range from blocked roads to possibly huge property damage and many deaths.

Soil Liquefaction
This happens when the movement caused by an earthquake forces water to seep into the material beneath a building. This causes saturated granular material to lose its strength and briefly change into a liquid from a solid. This forces the foundations of structures to become very unstable and sink into the ground.

Fires
Earthquakes can easily cause fires. Ground movements can lead to gas and fuel leaks in pipes, cutting off electrical cables, etc. The destruction of water pipes makes it harder to fight such fires should they occur. The Earthquake of 1906 in San Francisco ruptured the main water supply, and as a result, there was extensive fire damage.

When the earthquake is over, review what has occurred.

  • Check on the status of your family’s physical health and the safety of your home.
  • You will probably be on your own for three days or more if roads or bridges are damaged and/or blocked. Be prepared to take care of your family until help arrives.
  • Take one step at a time and pay attention to the mental health of your family.

After you've recovered:

  • Restock your Supplies Kit.
  • Review and update your personal emergency plan.
  • Get trained and volunteer so you can help others in your community.
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