Seismic and gravity constraints on plate flexure and mantle rheology along the whole Hawaiian-Emperor seamount chain

The Hawaiian-Emperor seamount chain is a hotspot-generated intraplate volcanic chain that has yielded key constraints on the rigidity of Earth's tectonic plates. However, previous studies have shown significant variability in the effective elastic thickness, T_e, a proxy for the long-term strength of the lithosphere, along the chain. While low T_e (10-20 km) at the Emperor Seamounts and high T_e (17-37 km) at the Hawaiian Ridge are expected because of their differences in volcano and plate age, the change between them appears abrupt and occurs in the vicinity of the bend in the chain. To investigate this variability, we estimated T_e along 3000 profiles - spaced 2 km apart along the chain - from gravity and flexure modeling, calibrated using constraints from deep seismic experiments carried out in 2018 and 2019. Here we show that, contrary to previous predictions, T_e changes gradually along the chain and that weak zones can exist within the interior of a large, otherwise rigid, plate and may, we speculate, facilitate the initiation of intra-oceanic subduction in response, for example, to changes in plate motion and eventually lead to their break-up.