Seismic Hazard and Risk: Fragility and Vulnerability of Housing in Lombok Island, West Nusa Tenggara, Indonesia, in Response to 2018 Earthquakes

Abstract:

A series of earthquakes struck Lombok Island, West Nusa Tenggara, Indonesia, in 2018. The first earthquake occurred on July 29 with magnitude Mw 6.4. A week later, the second earthquake hit the island on August 5 with magnitude Mw 6.9. The third major event struck on August 19 with Mw 6.3 and ten hours later, the last major earthquake occurred with Mw 6.9. There were hundreds of aftershocks that followed the main events with the largest recorded magnitude was Mw 5.9. The earthquakes killed over 500 people, injured thousands, and near half million people were displaced. The intensity of ground shaking resulted in over 120,000 damaged houses and hundreds public facilities (health centres, mosques, and schools). This natural disaster occurred two years ago and until now there have been few studies related to the series of earthquakes. This study emphasizes seismic hazard and risk analysis with a focus on developing housing vulnerability and fragility models for Lombok Island. The research involves post-event surveys to gather information about building structure types and level of damage as well as ground motion analysis using GMPEs suitable for Lombok Island (Abrahamson, et al, 2014; Boore, et al, 2014; Chiou and Youngs, 2014; Campbell & Bozorgnia, 2014) and stochastic method. This research aims to fill the knowledge gap on how fragile and vulnerable the existing structure in Lombok under varying degree of seismic loading. The post-earthquakes surveys revealed there are five housing types in Lombok Island which are Unreinforced Masonry (URM), Concrete Hollow Block (CHB), Infill Masonry (IM), Confined Masonry (CM), and Wood Frame (WF). URM dominates the housing type in the island up to 70% and show poor performance with >50% in unrepairable condition. The percentages of CHB, WF, CM, and IM are 10%, ~8%, ~7%, and ~5%, respectively. The housing damage survey will be integrated with ground motion simulation result to produce fragility and vulnerability models of each building type useful for the Indonesian government in quantifying the seismic risk to reduce the impact of the future event.