why do some earthquakes cause more deaths than others

Why do some earthquakes cause more damage than others? If they occur near large urban areas with many people,
transport services, large buildings and services such as gas and electricity - there can be a great amount of deaths and damage In Poor countries - LEDC's they have poorly built buildings, few emergency facilities, and the equipment to help rescue people - a good term to use is that they have a poor infrastructure.


In rich countries - MEDC's such as the USA they prepare for an earthquake with drills and have a great deal of trained emergency personnel and equipment to go to help the injured.


They also try to build to withstand earthquake damage - ie The Transamerica building Earthquake's release compressional shear and surface waves with the surface waves being the slowest and most destructive. Depending on the material the Surface waves (Love and Rayleigh waves) pass through they will increase or decrease in amplitude or frequency.


Bedrock or solid material decreases the amplitude and frequency of these waves causing less overall shaking. Unconsolidated sediment however increases both amplitude and frequency causing more violent shaking.


This is why there can be pockets of more destruction and less destruction depending on the underlying stratigraphy. Buildings also oscillate at a certain frequency i. e. Tacoma narrows bridge (galloping girde) so if the frequency that the seismic waves are oscillating at match the buildings frequency it will cause it to engage in harmonic motion and eventually tear itself apart.


Smaller or shorter buildings tend to have higher frequencies whereas larger skyscrapers will oscillate at a lower frequency.