Quick Answer
Aftershocks can continue for months or even years after a primary quake, with some cases lasting up to 20-30 years. The frequency and intensity of aftershocks decrease over time but can still pose a significant risk. Aftershocks can cause widespread destruction and loss of life.
Aftershock Patterns and Risks
Aftershocks often occur in a predictable pattern, with the largest aftershock typically occurring within the first 24-48 hours. The magnitude of aftershocks usually decreases by about 0.5-1.5 units per day. This pattern can help you understand and prepare for the aftershocks that may follow a quake.
Building Collapse and Aftershocks
Buildings that are damaged during a primary quake are at a higher risk of collapse during aftershocks. This is because the structure may not be able to withstand additional stress, leading to a catastrophic failure. If you’re in a damaged building during an aftershock, prioritize evacuation over sheltering in place, as the risk of collapse may outweigh the benefits of seeking temporary shelter.
Dropping, Covering, and Holding
While the doorway myth suggests that standing in a doorway can provide safety during an earthquake, this is not a reliable method. Aftershocks can cause doors to swing violently, putting you at risk of injury. Instead, drop to the ground, take cover under a sturdy piece of furniture or a reinforced doorway, and hold onto the furniture to prevent being knocked over. This can significantly reduce your risk of injury during aftershocks.
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