Christchurch Earthquake Aftermath. Christchurch, Canterbury, New Zealand. February 22, 2011.
The most obvious danger brought by earthquakes is shaking ground. Depending on its intensity, this motion itself can damage or destroy building materials, which get stretched and bent beyond their tolerances. The ground’s movement can take the form of waves running along the surface of the ground. As the wave runs under a building, the structure can lean, potentially tipping over. Then, when the shaking stops, the ground often settles to a different level compared to where it was previously, causing buildings, roads, and other structures to become unstable, topple, or break apart. Shaking ground can also trigger other types of ground movement, unleashing landslides, avalanches, or mudslides, especially in mountainous regions.
An automobile lies crushed under the third story of this apartment building in the Marina District. The ground levels are no longer visible because of structural failure and sinking due to liquefaction. Loma Prieta, Marina District of San Francisco, California, USA. October 17, 1989.
Another phenomenon caused by shaking ground is soil liquefaction. This happens when the shaking ground stirs up groundwater, mixing this water with soil near the surface. The result is a new, soft soil mixture that behaves like quicksand. When soil liquefaction happens below a building, the previously stable soil underneath the structure transforms into mush, causing the building to sink, tip, or break apart. Once the earthquake stops, the groundwater will gradually seep back down into the earth, allowing the soil near the surface to become firm once again. As the soil firms, the building will stop settling and come to rest in its altered position. Liquefaction is particularly common in places with sandy soil and groundwater at shallow depths in the soil.
Displacement along Fault Lines
When an area containing a fault line gets hit by an earthquake, the land can break into new masses, separated by the fault line. Structures that were built across the fault will then be cleaved apart. If a road, for example, happens to cross the fault line, it can be sliced apart at the fault, with the two new pieces separated by a chasm or even pushed past each other, depending on the movement of the earth’s plates.
An aerial view of Minato, Japan, a week after a 9.0 magnitude earthquake and subsequent tsunami devastated the area. March 18, 2011.
Floods
Earthquakes often bring a serious risk of flooding, due to the fact that they can destroy natural or manmade barriers that hold water in place. Dams can be weakened to the point of failure, or toppled entirely, by an earthquake. The water, previously restrained by the dam, will immediately follow gravity’s path to lower ground, submerging, damaging, or sweeping away anything in its path.
Earthquakes along the ocean floor can cause tsunamis, giant tidal waves bringing immense destruction to coastal areas they hit. A similar phenomenon, called a seiche, can occur on lakes. Although seiches are usually smaller than tsunamis, they are still capable of destroying lakefront property if the earthquake has sufficient force.
Fires
Earthquakes can also cause fires by pulling down power lines, ripping apart gas pipes, or toppling wood burning stoves or fireplaces. Although the resulting fires can vary in severity, their effect is often worsened as the earthquake disrupts emergency crews’ ability to extinguish them.
Image sources: shelby-dog, U.S. Geological Survey, and Ethan Johnson
--------------
This article is intended for informational purposes only. Before beginning any construction project at your home or taking steps to prepare for an emergency, please ensure that you take necessary safety precautions; consult construction professionals, your local authorities, and disaster safety experts whenever necessary. Water Damage Defense accepts no responsibility for the actions you take during an emergency or as you prepare for one.