Estimating tsunami run-up

Abstract

Tsunami risk reduction activities rely on a sound knowledge of the hazard characteristics. Our understanding of these characteristics is derived from empirical measurements, numerical models or established rules. Conventional methods used to delineate areas vulnerable to tsunami inundation are often calculated from estimated maximum wave height at the coast and ''rules-of-thumb''. Applying such rules may give unreliable results for decision-makers. Using basic hydraulic principles and assumptions, this paper improves on the existing rules by developing and testing new equations for predicting tsunami maximum depth profiles and inundation distances. The proposed equations require knowledge of shoreline wave-crest level, the onshore ground profile and an index for onshore roughness (a ratio of distance between protrusions to a local friction factor). As a tsunami wave moves inland, the equations demonstrate that there will usually be an exponential decline in peak water depth. The equations also confirm that a smaller spacing between onshore roughness elements, such as trees or houses, will give a steeper decline in peak depth due to increased friction as a wave moves inland. Furthermore, where ground level is rising faster than friction head is being lost, it is predicted that the water level of a tsunami will rise above the shoreline wave-crest level. The ground slope at which run-up starts to exceed shoreline wave-crest level can be predicted from the shoreline wave-crest level and roughness spacing. Results predicted by the new equations are verified by comparison with tsunami run-up measurements made in Samoa and Java.

Effects of Source Faulting and Fringing Reefs on the 2009 South Pacific Tsunami Inundation in Southeast Upolu, Samoa

“…Nevertheless, our observations corroborate that tsunamis are highly sensitive to source parameters, with significant spatial inundation variability for a given source model. In addition, the observations suggest that one-dimensional tsunami attenuation modeling of offshore wave heights at coast, which is sometimes used to estimate tsunami inundation hazard, is not adequate for use in reef fringed islands (e.g., Smart et al, 2015 10.1029/2020JC016537 Figure 8. Sequence of inundation due to the first tsunami wave for scenario Lay et al (2010) Version C at Lepa and Saleapaga.…”

Post-earthquake cordons and their implications

“…The Wellington CBD shown in Figure 4, for example, is a city where such a response plan would be useful, as the advised tsunami evacuation zones overlap much of the CBD. Mapping tsunami inundation and exposure in high-risk locations is an active area of research (Dall’Osso et al, 2014; Smart et al, 2016; Usha et al, 2012). Where a potential cordon zone is identified, effective communication to the public about its purpose and location is essential, to help build trust and avoid confusion and uncertainty in the local population.…”

Effects of source faulting and fringing reefs on the 2009 South Pacific tsunami inundation in southeast Upolu, Samoa

“…Nevertheless, our observations corroborate that tsunamis are highly sensitive to source parameters, with significant spatial inundation variability for a given source model. In addition, the observations suggest that one-dimensional tsunami attenuation modeling of offshore wave heights at coast, which is sometimes used to estimate tsunami inundation hazard, is not adequate for use in reef fringed islands (e.g., Smart et al, 2015).…”