Proposal of a depth-based tsunami intensity scale for coastal buildings based on building vulnerability index: A contribution towards an integrated tsunami intensity framework

Tsunamis pose a persistent threat to coastal regions particularly to its dense population and the built environment. One of the key components in managing tsunami risks lies in understanding its intensities. Understanding potential intensity in correlation with tsunami's characteristics and the vulnerability of at-risk elements are essential for an effective tsunami risk management. This study proposes an eight-grade tsunami intensity scale centered on identifying potential damage to coastal buildings. A Building Vulnerability Index (BVI) which is utilized to determine vulnerability levels of coastal buildings was refined through an expert opinion survey. Additionally, field data from three major tsunami events, each triggered by different mechanisms, provided empirical data for the construction of the scale. Ordinal regression analysis was conducted on the sampled buildings to link inundation depths and damage states across four building vulnerability classes. Results from the analysis provide evidence that more vulnerable buildings reach substantial damage states at lower inundation depths compared to more resilient buildings. Following this, a tsunami intensity scale with eight discrete grades was constructed to offer a simple yet robust tool that is intended to streamline this approach for local stakeholders, particularly where complex data or assessment technique remains inaccessible or unfeasible. The study concluded that the proposed scale can be further refined as more post-tsunami survey data particularly from different regions and source events become available. In addition to refining the BVI formulation, tsunami induced currents, or other hydrodynamic drivers can be integrated in future iterations to move towards an integrated tsunami intensity framework.