6.7: Hazards from Earthquakes

Hazards from Earthquakes

Earthquakes are among nature’s most destructive phenomena, and there are numerous hazards associated with them. Ground shaking can lead to falling structures, making it the most dangerous earthquake-related hazard. The intensity of ground shaking depends on several factors, including the size of the earthquake, the duration of shaking, the distance from the epicenter, and the material the ground is made of. Solid bedrock will not shake much during a quake, rendering it safer than other ground materials. Typically, seismic waves will amplify as they encounter weaker geologic materials (sediments), and this amplification can be destructive (Figure 6.16).

Watch the video below on amplification.

In addition to wave amplification, loose, water-saturated sediments or artificial fill can serve as sites for liquefaction Links to an external site.. Normally, friction between grains holds them together; however, as unconsolidated sediments are shaken, water surrounds every grain, eliminating the friction and allowing them to liquefy (Figure 6.17). Liquefaction can cause major damage to buildings and infrastructure, sand and water to be ejected in “sand volcanoes Links to an external site.”, and the ground surface to be permanently deformed. 

 

Want to see a fun experiment? Check out this video below:

 

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Large (M7.5+) earthquakes typically displace the seafloor, which can trigger tsunamis Links to an external site.. These large ocean waves are often associated with subduction zone earthquakes. The Sumatra-Andaman earthquake in 2004 Links to an external site. triggered a tsunami in the Indian Ocean that resulted in almost 230,000 deaths. In 2011, the Tohoku earthquake Links to an external site. off the coast of Japan triggered a tsunami wave that heavily impacted the country, killing more than 15,000 and causing the meltdown of the Fukushima Daiichi Nuclear Power Plant.

Earthquakes can also 1) ignite fires, like the conflagration experienced following the Great San Francisco Earthquake Links to an external site. of 1906, 2) result in major ground rupture, like the rupturing experienced during the Ridgecrest earthquakes in 2019 (Figure 6.18), and 3) trigger landslides, like. the more than 10,000 landslides experienced in the LA area in the wake of the Northridge earthquake in 1994. Typically, landslides will occur in areas with steep slopes, like the mountains, or underwater. Underwater landslides may also trigger tsunami, and, if coupled with a subduction zone earthquake, may result in a taller-than-predicted wave. Earthquake-prone areas can take steps to minimize destruction, such as implementing strong building codes, early warning systems, addressing poverty and social vulnerability, retrofitting existing buildings, and limiting development in hazardous zones. Earthquake forecasting Links to an external site. (Figure 6.19) can help communities plan for their future risk. Want to know your hazard potential? Visit the California Department of Conservation’s EQ Zapp: California Earthquake Hazards Zone Application Links to an external site..