Seismic Hazards

It is essential to study earthquakes because it is a very serious natural disaster that can strike at any moment in time without giving any signs at all. In this module, we will study more about this hazard in detail. We will be using the term ‘seismic hazard’ when referring to earthquakes and the effects it has. Here is an overview of what you will learn in this module:

  • The study of seismic hazards and how it can help to minimize the effects of earthquakes.
  • The effects of earthquakes on humans and the environment.
  • The different kinds of seismic hazards.

First, we need to define what seismic hazard is: It is the rate of possibility that an earthquake will happen in a certain geographic location, in an estimated time frame, and possesses a movement from the ground which can be measured through intensity levels.

Earthquake

These hazards comprise any physical event which can be linked with an earthquake that may create harmful effects on people’s everyday lives.

What hazards can earthquakes bring?

We can break these hazards into two classes: the main earthquake hazards and the secondary earthquake hazards. How can we differentiate them from each other? Let’s take a look.

Main earthquake hazards – these are hazards which can be directly associated with the occurrence of an earthquake. The examples of main earthquake hazards are:

  • Shaking of land – this is one of the scariest earthquake hazards that the disaster could bring. Its damage can be fatal depending on the intensity of the earthquake because the ground becomes unstable and begins to move violently.
    The trembling is associated with the ease that the earthquake waves pass through the earth’s surface. This triggers the energy stored in stressed rocks to release when a fault has been moved.
    There are several factors that need to be considered when measuring the damage that earthquakes bring, including:

    • The intensity of the land movement.
    • The duration of the land movement.
    • The frequency of the land movement.
    • The possibility of recurrence of the land movement.

 

  • Landslide – this is another seismic hazard that must be taken seriously as it can cause a big impact in terms of damages and casualties. These landslides are caused by a forceful land motion from the pressure of the earthquake. This can cause the less stronger slopes to start sliding.
Landslide
  • Liquefaction – this is a seismic hazard that happens when there is a reduction in the sturdiness of the soil due to the shaking of the land. This seismic hazard can be linked to the massive number of damage. It often begins in saturated soils as these soils have a gap between particles which is packed with water. Liquefaction is often triggered by an earthquake which produces floods as a consequence.
Liquefaction
  • Surface Rupture – this is the tearing apart of a structure because the two sides of the fault slide against each other.
Surface Rupture

Secondary earthquake hazards – these seismic hazards happen due to the assistance of the main hazards. Although they are secondary to the main hazards, they can sometimes be more destructive than the main hazard.

  • Tsunami – this seismic hazard is often earthquake-induced. It is a chain of waves that are produced in a body of water because of a system that produces motion in the water column.
    Tsunami

    Some examples of the systems that can produce tsunamis aside from earthquakes are:

    • Volcanic activities
    • Landslides
    • Explosions that are caused by bombs from illegal fishing.

Tsunamis can greatly affect coastlines which can cause a massive amount of damage to assets and life.

  • Seiche – this is a vertical wave in an enclosed water body. It is often generated by shock waves from earthquakes. These seiches are most common in bays, harbors, lakes, and swimming pools.
Seiche
  • Flooding – this is generated by tsunamis which is a secondary earthquake hazard. Large amounts of water rush into land areas, causing damage and destruction to homes, buildings, cars, and trees.
Flood
  • Fires – this seismic hazard happens when a strong earthquake causes electrical damage to structures which can eventually turn into a fire.
Fires
  • Mudflows – this occurs whenever there is an onset of landslides with the added water from rains or other foreign substances. It can affect a region or community dramatically.
Mudflows

These are the seismic hazards that you can expect when there is an earthquake.

Have you ever wondered what the preventive measures are and the actions that we can do to minimize its effects? The following are actions that we can take:

  • During earthquakes, find a secure place, like a sturdy table, and hide under it. Cover your head with your hands and arms.
  • The government ensures that buildings have passed the standards of safety to assure that it will not tremble when an earthquake happens.
  • Attend earthquake drills so you know what to do if an earthquake strikes.
  • Stay away from coastal areas when an earthquake occurs because a tsunami can strike at any point.
  • Develop an emergency plan so you will be ready when there is an earthquake.

To conclude, you have studied the different seismic hazards, so you now have an idea of how an earthquake can be a nightmare for all of us – humans, plants, and animals as well as our infrastructure. However, with proper knowledge and preparation, the effects and casualties due to the above hazards can be minimized.

 

Image sources:
  1. Landslide: https://commons.wikimedia.org/wiki/Landslide
  2. Seiche: https://commons.wikimedia.org/wiki/File:Seiche_on_Saginaw_Bay_(20878994180).jpg
  3. Fires: https://commons.wikimedia.org/wiki/File:Napa_Sonoma_fires.jpg
  4. Tsunami: https://commons.wikimedia.org/wiki/File:Damage_of_Tsunami_in_Tagajo.JPG
  5. Floods: https://commons.wikimedia.org/wiki/File:Flood102405.JPG
  6. Mudflow: https://commons.wikimedia.org/wiki/File:Armero_Mudflow_and_ruins.jpg
  7. Liquefaction: https://en.wikipedia.org/wiki/Soil_liquefaction
  8. Earthquake: https://www.researchgate.net/figure/A-building-destroyed-by-the-earthquake-Wikimedia_fig3_326821510
  9. Rupture: https://en.wikipedia.org/wiki/Earthquake_rupture