Video Content Analysis of the 2018 Sulawesi Tsunami, Indonesia: Impact at Palu Bay

摘要

Water surface disturbances at two locations were captured by two separate witness videos few minutes before the Sulawesi tsunami hit the Palu City, Indonesia on Sep 28, 2018. One of these videos shows top-view of both locations with surface disturbances. The other video shows the side-view of one of the locations with surface disturbance (also recorded in the top-view video), as a fast-moving bore (broken wave with splash). This work performs a Video Content Analysis (VCA) to locate these surface disturbances and to give a rough estimate of the wave characteristic and evolution when the videos were recorded. For the top-view video, VCA was done on a single frame that depicts two observable areas of tsunami generation with a pair of tall sharp-crested waves (unbroken waves). Width of the wave fronts and height of the tall sharp-crested waves are determined using this selected frame. For the side-view video, a sequence of video frames were used to determine the splash height, wave speed and acceleration of the fast-moving bore. In addition, our work points out some similar wave characteristics between the tall sharp-crested waves observed in the videos and waves generated by a submarine landslide lab experiment from the literature. Using simple tools, e.g., Google Earth for three-dimension measurement and satellite view and basic geometrical optics methods, we give a rough estimate of the wave size, velocity and acceleration during the recorded time. As per the results, the observable tall sharp-crested wave fronts have approximate widths of 383 and 461 m and crest-trough heights about 24 and 29 m. The fast-moving bore has an average speed of approximately 22 m/s (78 km/h) with an acceleration of similar to 1:18 m/s(2). This work provides information which cannot be retrieved by post-event field survey, and we consider that the information could be useful for numerical modelers to validate their simulations, sources and model physics by comparing quantitatively to res