Abstract
Tephra from large explosive eruptions can cause damage to buildings over wide geographical areas, creating a variety of issues for post-eruption recovery. This means that evaluating the extent and nature of likely building damage from future eruptions is an important aspect of volcanic risk assessment. However, our ability to make accurate assessments is currently limited by poor characterisation of how buildings perform under varying tephra loads. This study presents a method to remotely assess building damage to increase the quantity of data available for developing new tephra fall building vulnerability models. Given the large number of damaged buildings and the high potential for loss in future eruptions, we use the Kelud 2014 eruption as a case study. A total of 1154 buildings affected by falls 1–10 cm thick were assessed, with 790 showing signs that they sustained damage in the time between pre- and post-eruption satellite image acquisitions. Only 27 of the buildings surveyed appear to have experienced severe roof or building collapse. Damage was more commonly characterised by collapse of roof overhangs and verandas or damage that required roof cladding replacement. To estimate tephra loads received by each building we used Tephra2 inversion and interpolation of hand-contoured isopachs on the same set of deposit measurements. Combining tephra loads from both methods with our damage assessment, we develop the first sets of tephra fall fragility curves that consider damage severities lower than severe roof collapse. Weighted prediction accuracies are calculated for the curves using K-fold cross validation, with scores between 0.68 and 0.75 comparable to those for fragility curves developed for other natural hazards. Remote assessment of tephra fall building damage is highly complementary to traditional field-based surveying and both approaches should ideally be adopted to improve our understanding of tephra fall impacts following future damaging eruptions.
Highlights
With populations surrounding volcanoes growing faster than the average global rate, eruptions will increasingly impact human settlements and livelihoods (Barclay et al, 2019; Freire et al, 2019)
Locations in which to assess building damage were selected based on the availability of high-resolution satellite imagery (30–70 cm pixels), the desire to record damage in areas where the most severe damage was reported to have occurred as well as across a wide range of tephra fall hazard intensities, as this is advised for accurate vulnerability assessment (Rossetto et al, 2014; Wilson et al, 2017)
Where K is the number of groups the data is split into for K-fold cross validation, Ntest set is the number of buildings in the test set whose damage state is being predicted and ncorrect predictions is the number of buildings whose predicted damage state matches the observed damage state
Summary
With populations surrounding volcanoes growing faster than the average global rate, eruptions will increasingly impact human settlements and livelihoods (Barclay et al, 2019; Freire et al, 2019). Media images and videos from some of the most heavily impacted villages do not feature any buildings that have experienced complete roof collapse (e.g. Berita Satu, 2014; Kreer, 2014) Inconsistencies between these reports, rapid building repairs and the wide area over which buildings were damaged all suggest remote sensing as an ideal method for assessing building damage from this eruption. Locations in which to assess building damage were selected based on the availability of high-resolution satellite imagery (30–70 cm pixels), the desire to record damage in areas where the most severe damage was reported to have occurred as well as across a wide range of tephra fall hazard intensities, as this is advised for accurate vulnerability assessment (Rossetto et al, 2014; Wilson et al, 2017). None of the roof cladding has changed colour and the structure of the roof is the same
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