On March 20th, 2005, the West Off Fukuoka Earthquake (M 7.0) occurred near northern Kyushu, Southwest Japan. This earthquake caused a significant amount of damage on Genkai Island off the coast of Fukuoka City. However, minimal damage occurred on mainland Kyushu. On October 23rd, 2004, the Niigata-Ken Chuetsu Earthquake (M 6.8) occurred, resulting in extensive damage despite its relatively small magnitude. Thick, soft sedimentary layers in the Chuetsu area caused the speed of seismic wave propagation to decrease, while the waves themselves were amplified. Sedimentary layer thickness is directly related to the amount of damage that occurs when an earthquake occurs.