First observations of the seiche that shook the world

TL;DR

This paper reports the first direct observations of a global seiche linked to mega-tsunamis in Greenland, using satellite altimetry and seismic data, validating previous theories and demonstrating new methods for studying extreme oceanic events.

Contribution

It provides the first direct observational evidence of a seiche caused by mega-tsunamis, using satellite data and advanced modeling, and introduces methods to analyze sparse altimetric data.

Findings

Validated seiche theory with direct satellite observations

Estimated initial seiche amplitude at 7.9 meters

Highlighted satellite altimetry's role in studying extreme events

Abstract

On September 16th, 2023, an anomalous 10.88 mHz seismic signal was observed globally, persisting for 9 days. One month later an identical signal appeared, lasting for another week. Several studies have theorized that these signals were produced by seiches which formed after two landslide generated mega-tsunamis in an East-Greenland fjord. This theory is supported by seismic inversions, and analytical and numerical modeling, but no direct observations have been made -- until now. Using data from the new Surface Water Ocean Topography mission, we present the first observations of this phenomenon. By ruling out other oceanographic processes, we validate the seiche theory of previous authors and independently estimate its initial amplitude at 7.9 m using Bayesian machine learning and seismic data. This study demonstrates the value of satellite altimetry for studying extreme events, while also highlighting the need for specialized methods to address the altimetric data's limitations, namely temporal sparsity. These data and approaches will help in understanding future unseen extremes driven by climate change.