The Use of Intensity Scales In Exploiting Tsunami Historical Databases

Abstract:

Post-disaster assessments for historical tsunami events (>15 years old) are either scarce or contain limited information. In this study, we are assessing ways to examine tsunami impacts by utilizing data from old events, but more importantly we examine how to best utilize information contained in tsunami historical databases, in order to provide meaningful products that describe the impact of the event. As such, a tsunami intensity scale was applied to two historical events that were observed in New Zealand (one local and one distant), in order to utilize the largest possible number of observations in our dataset. This is especially important for countries like New Zealand where the tsunami historical record is short, going back to only the 19th century, and where instrument recordings are only available for the most recent events. We found that despite a number of challenges in using intensities -uncertainties partly due to limitations of historical event data - these data with the help of GIS tools can be used to produce hazard maps and offer an alternative way to exploit tsunami historical records. Most importantly the assignment of intensities at each point of observation allows for utilization of many more observations than if one depends on physical information alone, such as water heights. We hope these results may be used towards developing a well-defined methodology for hazard assessments, and refine our knowledge for past tsunami events for which the tsunami sources are largely unknown, and also for when physical quantities describing the tsunami (e.g. water height, flood depth, run-up) are scarce.