Earthquakes are an example of seismic activity created by plate boundaries. They can be caused by the subduction of oceanic crust which is densest at 2.9 g/cm3 under continental crust which weighs 2.7g/m3 at destructive plate boundaries. Earthquakes can also occur along conservative plate boundaries such as that shared by the Pacific and North American plates which move at 5-9 cm/year and 2-3 cm/year respectively causing the 1994 Los Angeles earthquake along the San Andreas fault alongside which lies the San Gregorio and Hayward faults. Earthquakes have different impacts dependent on the location of their foci, the point at which they originate from underground, the presence of land in the surrounding areas, but also the human factors such as land use, population density and the use of earthquake proofing technologies to limit earthquake impacts.
The Boxing Day tsunami in 2004 was created due to an earthquake along the 3 plate junction where the Philippine, Pacific and Eurasian plates all meet. The 15-20 m slip along a 1600km slip plane created an earthquake measures at 9.1 on the logarithmic Richter scale making it one of the most intense earthquakes in history. It caused a tsunami wave which resulted in the deaths of 180000 people according to a UN report, though other sources suggested it reached 300000. The Kobe earthquake which devastated the port of Osaka Bay resulted in 6300 deaths and 35000 serious injuries. This earthquake measured 7.1 on the Richter scale meaning that it was less powerful as each step up the scale is a 10 fold increase in power and a 30 fold increase in intensity. The impacts in terms of death were vastly different as a result of the lower reading on the scale and therefore it can be argued that natural factors such as the origin of the earthquake and its force are important factors in determining the impact of earthquakes.
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