Many seismologists have said that Earthquakes do not kill people, building do. This is because most deaths from earthquakes are caused by buildings or other human constructions falling down during an Earthquake. Earthquakes located in isolated areas far from human population rarely cause any deaths. Thus in earthquake prone areas, strict building codes requiring the design and construction of buildings and other structures that will withstand a large earthquake will reduce the death toll.
Damage from Earthquakes.
- Ground Shaking: Shaking of the ground caused by the passage of seismic waves near the epicenter of the earthquake is responsible for the collapse of most structures. The intensity of ground-shaking depends on distance from epicenter and on the type of bedrock underlying the area. In general, loose unconsolidated sediment is subject to more intense shaking than solid bedrock. Damage to structures from shaking depends on the type of constructions. Concrete and masonry structures, because they are brittle and are more susceptible to damage than wood and steel structures which are more flexible.
- Ground Rupture: Ground rupture only occurs along the fault zone that moves during the earthquake. Thus structures that are built across fault zones make collapse, where as structures built adjacent to, but not crossing the fault, may survive.
- Fire: Fire is a secondary affect of earthquakes. Because power lines may be knocked down and because natural gas lines may rupture due to an earthquake, fires are often started closely following an earthquake. The problem is compounded if water lines are also broken during the earthquakes since there will not be a supply of water to the extinguish the fires once they have started. In 1906 earthquake in San Francisco, more than 90 % damage to buildings was caused by fire.
- Rapid Mass Wasting Process: In mountainous regions are subjected to earthquakes, ground-shaking may trigger rapid mass-wasting events like rocks and debris falls, rocks and debris slides, slumps, and debris avalanches.
- Landslides and Avalanches: Earthquakes can cause landslides and avalanches, which may caused damage in hilly and mountainous areas.
- Tsunamis: Tsunamis are giant ocean waves that can rapidly travel across oceans. Earthquakes that occur along coastal areas can generate tsunamis, which can cause damage thousand kilometers away on the other side of ocean. For examples, the 2004 Indian Ocean earthquakes.
- Impacts on Humans: Earthquakes can cause diseases, lack of basic necessities, loss of life, general properly damage, road and bridges damage, and collapse of buildings or destabilization of the foundations of building which may lead to collapse in future earthquakes. This can cause total devastation for those affected as the country may not have the funds for regeneration of lives and possessions. An earthquake can ruin someone’s life forever, only 3% buildings in Kobe, for instance, have earthquake in insurance; therefore un-enabling them to get back onto their feet again.
- Liquefaction: Liquefaction is a process that occurs in water-saturated unconsolidated sediments due to shaking. In areas underlying by such material, the ground-shaking causes the grains to loose grain-to-grain contact, and thus the material tends to flow. You can demonstrate this process to yourself if you go to the beach. Stand on the sand just after an incoming wave has passed. The sand will easily support your weight and you will not sink very deeply into the sand if you stand still. But if you started to shake your body while standing on this wet sand, you will notice that the sand begins to flow as a result of liquefaction, and your feet will sink deeper into the sand.
Measurement of an Earthquake