What are the two factors that can determine the amount of destruction that results from an earthquake?

Answer 1

• Their magnitude (the amount of energy released by the earthquake, which effects the energy of the seismic waves and the damage they can cause).
• The proximity of the epicentre to populated or urban areas (the closer the earthquake epicentre, the more energy will be retained by the earthquake waves and the greater the damage)
• The local ground conditions (seismic waves have a much lower amplitude in hard rock than in soft ground making the damage caused by seismic waves much greater in soft grounds. Also liquefaction may occur in soft ground where there is pore water which acts to significantly reduce bearing capacity and makes building collapse much more likely)
• The construction techniques employed in the area and the enforcement of applicable construction codes or standards will affect how destructive an earthquake is (earthquake resistant designs will obviously reduce the damage caused by seismic waves, on the other hand, in countries or areas where poor building practices are followed - e.g. insufficient steel reinforcement in concrete, the use of cheap or poorly sourced aggregates which reduce the strength of concrete or the construction on poor founding materials without the requisite foundation engineering will all act to increase the damage caused by earthquakes).