Source rupture characteristics and ground motion simulation of the southernmost Ryukyu subduction zone 31 March 2002 Mw7.1 earthquake

Abstract

An Mw 7.1 Ryukyu subduction zone earthquake struck northern Taiwan in 2002. The joint source inversion result indicates that rupture mainly propagated toward the northwest and produced a significant directivity. The long-period strong ground motion observed in northern Taiwan was directly related to source rupture effects. To assess the seismic risk in Taiwan and even East Asia more generally, it is necessary to carefully consider the various types of megathrusts that occur in the southern Ryukyu subduction zone. • An Mw 7.1 Ryukyu subduction zone earthquake struck northern Taiwan in 2002. • Rupture mainly propagated toward the northwest resulted in a strong directivity. • Long-period strong ground motion was directly related to source rupture effects. • Megathrust in Ryukyu subduction needs to carefully consider to assess seismic risk. On March 31, 2002, a magnitude 7.1 earthquake occurred off the coast of eastern Taiwan. The Taipei 101 Financial Building was under construction at that time and due to extremely strong long-period shaking, two cranes on the top floor collapsed and fell to the ground, killing five people. This earthquake was caused by a rupture of the southern Ryukyu subduction zone. The result of a joint source inversion showed that the slip originated at the mid-depth subduction interface off the eastern coast and then propagated to the western fault plane with a rupture velocity of approximately 3.0 km/s. Forward ground motion simulation indicated that the main cause of the long-period strong motion in northern Taiwan was directly related to source effects, including long rupture lasting, rupture directivity and source radiation. The seismic waves were further amplified by the soft sediments in the Taipei basin which also resulted in longer vibration time in Taipei City.