Cataloguing tephra fall building damage and vulnerability using remotely obtained data: 2020 Taal eruption, Philippines

Abstract

The 2020 eruption of Taal volcano, Philippines deposited tephra 85 km away in the northern parts of the National Capital Region of the Philippines. Threats of an imminent eruption followed by impacts from widespread tephra falls displaced almost 400,000 citizens and caused widespread building damage. Cataloguing the tephra-falls and analysing their impacts will facilitate measures to build resilience for future eruptions. We used remotely obtained data to create tephra-fall isopach maps as well as to catalogue the damage caused to buildings due to tephra-fall. Three isopach maps were created using different scenarios to understand how different data sources and methods of creation can affect the maps. A six-level damage state (DS) framework was created to classify building damage and was used with the isopach maps to create fragility curves for all DS. The median exceedance load (MEL) of roof collapse (DS4/5) was calculated to be 2.3 kPa and is in line with various other vulnerability papers studying similar roof types – metal sheets of varying conditions and corrosion. We also adapted a data quality framework to understand the effectiveness of using various remotely obtained data. In this paper, 96% (n = 240) and 100% (n = 1,626) of data to estimate tephra-fall thicknesses and building damage respectively were obtained from photographic evidence or aerial images, indicating future replicability and the potential usage of such data for future eruptions. Future work will include using better quality data in conjunction with exposure and probabilistic hazard studies to understand building risk in the area.