Inversion of ocean surface currents to obtain coseismic seafloor deformation.

During an earthquake, the coseismic deformation of the ocean floor is transmitted through the water column. If the earthquake’s energy is sufficiently large, it can uplift the ocean surface, and the subsequent collapse due to gravity leads to the propagation of waves as a tsunami. This perturbation also creates current fields, as water is pushed away from the uplifted area, which carry information about the seafloor deformation, including its rate and distribution. By measuring the surface current fields, information about the earthquake’s underwater spatial and temporal part characteristics can be obtainable. Using data measured directly above the source, in conjunction with onshore measurements, may lead to better resolution of the inverted seismic source, especially near the shallower parts of the rupture, complementing traditional inversion methods, such as geodetic data based models. 
As a first step, this work presents a method for inverting the sea surface current field induced by coseismic deformation, isolated from background currents such as tidal or wind-driven currents, to determine the distribution of deformation at the sea bottom, assuming a flat ocean floor and instantaneous deformation. We use a simple linear fluid model to relate the coseismic effects to surface ocean currents and test robust inversion methods, assessing the associated uncertainties, using synthetic data and, as a benchmark, the deformation distribution from the 8.8 2010 Mw Maule earthquake. This approach offers novel insights into the use of new datasets for retrieving seismic source information.