TSUNAMI MAGNITUDE SCALE BASED ON DEEP-OCEAN ASSESSMENT AND REPORTING OF TSUNAMIS (DART) BUOY WAVE HEIGHT DATA

A variety of methods have been developed to calculate tsunami magnitude and intensity. Since most tsunami measurements are obtained from tide gauges at the shore, or run-up elevation and wave height observations from the coastline, it is difficult to create a tsunami magnitude scale that would exclude local effects resulting from different bathymetry and coastal geometries.

This project aims to address this issue by developing a new tsunami magnitude scale that will utilize deep ocean measurements. Since Deep-Ocean Assessment and Reporting of Tsunamis (DART) buoys are located in the deep ocean, the data these buoys provide will avoid the local effects; thus, giving us measurements that reflect the physical properties of the source more accurately. With this, we also aim to improve our understanding of the relationship between earthquakes and tsunamis, which will contribute to improved tsunami predictions.

This study analyzes DART buoy wave height data for six of the most significant earthquake-generated tsunamis in the last 15 years. These data are used to directly measure the maximum tsunami wave heights in the deep ocean. To develop a tsunami magnitude scale based on these data, we use an approach similar to the original method to calculate local earthquake magnitudes, as developed by Charles Richter in the 1930s. The equation used to solve for a measure of the tsunami magnitude (𝑎_0𝑗) is

a_ij = a_0jr_ij^-nexp(-kr_ij)

where 𝑎_𝑖𝑗 is the observed wave height amplitude; i and j represent the station and the event, respectively; 𝑟_𝑖𝑗 is the distance between the source and the receiver; and, n and k are attenuation coefficients that will be the same for all stations and event pairings.

We have obtained tsunami wave height data from the DART buoys, and removed outliers and data from malfunctioning buoys. Preliminary results show that we can fit curves of the above form that represent the best fit to our data per event, supporting our hypothesis that we can develop a tsunami magnitude scale using this method. Our next goal is to obtain consistent values for n and k, which can then be used to calculate 𝑎_0𝑗 per event and subsequently develop a tsunami magnitude scale based on those values.