The Vanuatu subduction zone is known for its high level of seismic activity, where the Australian Plate is subducted beneath the Vanuatu arc. In particular, the southern segment of the subduction zone, located to the west of the Erromango, Tana, and Anatom islands, has been the site of two major earthquakes in the past century and a half: one on March 28, 1875, and another on September 20, 1920.

Despite the significant impact of these earthquakes, their magnitudes have never been accurately determined due to the lack of quantitative data available from before the installation of seismic instruments in 1976.

Both of these earthquakes resulted in tsunamis, but without sufficient tide gauge or paleo-tsunami records, it has been challenging to assess their magnitudes accurately using tsunami inversion techniques.

However, historical records from the Loyalty Islands to the west of the Vanuatu arc have provided detailed descriptions of the impacts of these tsunamis. By comparing these eyewitness accounts with simulated tsunami runups based on realistic earthquake scenarios, it may be possible to estimate the magnitudes of these historical earthquakes with greater precision.

The Loyalty Islands have a history of being impacted by tsunamis generated from local earthquakes, with two destructive tsunamis recorded in 1875 and 1920. Despite limited quantitative data on these events, witness reports and knowledge of the local tectonic context have been crucial in understanding past tsunamis and assessing future tsunami hazards in the region.

To better understand the tsunami hazard facing the Loyalty Islands, this study utilizes historical accounts, tectonic information, and advanced tsunami modeling techniques to create a deterministic tsunami map for the region. By reconstructing past earthquake.

Analysis of historical records from both the March 28th 1875 and September 20th 1920 tsunamis reveals significant impacts on the Loyalty Islands.

Reports from Catholic missionaries on Lifou following the 1875 earthquake indicated a tsunami of notable magnitude. Geological studies in the region suggest a kinematic context of subduction between the Southern Vanuatu and Loyalty Islands, with an estimated horizontal velocity.

Based on this data, a series of earthquake scenarios were developed to model potential ruptures in the offshore Loyalty Islands. Utilizing a tsunami propagation model, the study analyzed runup estimates for the 1875 and 1920 events, detailing the simulated impacts on various coastal sites. The findings provide insights into potential future seismic activity in the region and are supported by collaborations with research institutions and governmental agencies.

Re written from a article by science direct see full article HERE