Earthquake Fingerprint of an Incipient Subduction of a Bathymetric High

Abstract

The resistance of bathymetric highs to subduction results in large‐scale morphological distortions of the outer‐rise, trench, and fore‐arc regions. Once subducted, bathymetric highs induce frictional segmentation along the plate interface that may result in increase or decrease of the plate coupling. However, the mechanics of the collision is inferred mostly from geophysical and geological surveys since earthquakes rarely illuminate finer details of the subduction of seafloor relief. A year‐long and energetic seismic sequence at the Loyalty Ridge (LR)‐Vanuatu Trench allowed us to characterize how strain is released along the collision zone. Earthquakes revealed complex fracturing in the outer‐rise and fore‐arc regions and segmentation of the interface with both limited magnitude events and aftershock productivity. The complex earthquake activity associated to the collision and subduction of the LR appears to support a frictionally segmented interface where Mw ≥ 8 megathrust earthquakes are unlikely to nucleate.

Seamount Subduction and Megathrust Seismicity: The Interplay Between Geometry and Friction

“…Observations from natural cases support contradictory theories on the relationship between seamounts and large megathrust earthquakes (Mochizuki et al., 2008; Scholz & Small, 1997; Wang & Bilek, 2011, 2014). Despite the simplicity of our models, our findings are consistent with the hypothesis that seamounts act as seismic barriers, decreasing both seismic coupling and maximum magnitude of earthquakes (von Huene, 2008; Mochizuki et al., 2008; Wang & Bilek, 2011, 2014; Todd et al., 2018; Passarelli et al., 2022). Seamounts likely act as a barrier to rupture propagation due to a fracture network forming in the upper plate, which decreases seismic coupling and increases creep (Wang & Bilek, 2011, 2014).…”

“…In this area, the presence of seamounts enhances weak interplate coupling (von Huene, 2008; Mochizuki et al., 2008; Wang & Bilek, 2011, 2014) that promotes the nucleation of shallow slow slip events, tsunami earthquakes and microseismicity, and controls the location of tectonic tremors. Observations from the Loyalty Ridge confirm how the presence of bathymetric highs along the subduction zone leads to the development of a complex deformation pattern, and possibly inhibits the occurrence of earthquakes with Mw > 8 (Passarelli et al., 2022). Observations at natural subduction zones suggest that two main mechanisms (i.e., development of the upper plate fracture network and lower friction due to sediments rich in fluids) associated with subducting seamounts are responsible for stress heterogeneities and, in turn, promote earthquakes of relatively lower magnitude.…”

“…However, it is still not clear whether seamounts act as asperities, promoting ruptures (Bilek et al., 2003; Heuret et al., 2011; Scholz & Small, 1997; Thatcher, 1990) or barriers, inhibiting large earthquakes propagation (e.g., Collot et al., 2017; Kodaira et al., 2000; Marcaillou et al., 2016; Mochizuki et al., 2008; Morton et al., 2018; Wang & Bilek, 2011; Xia et al., 2021). Recent studies suggest that seamount subduction creates a fracture network along its path, promoting smaller earthquakes and creeping (Mochizuki et al., 2008; Passarelli et al., 2022; Wang & Bilek, 2011, 2014), but opposite scenarios have also been proposed in which seamounts indent the overlying plate, increasing normal stress and promoting large earthquakes (Bilek et al., 2003; Cloos & Shreve, 1996; Husen et al., 2002; Scholz & Small, 1997). Seamounts are also thought to influence pore fluid pressure and sediment consolidation and, in turn, megathrust strength and slip behavior.…”

Seamount subduction and megathrust seismicity: the interplay between geometry and friction.

“…Observations from natural cases support contradictory theories on the relationship between seamounts and large megathrust earthquakes (Mochizuki et al, 2008;Scholz & Small, 1997;Wang & Bilek, 2011. Despite the simplicity of our models, our findings are consistent with the hypothesis that seamounts act as seismic barriers, decreasing both seismic coupling and maximum magnitude of earthquakes (von Huene, 2008;Mochizuki et al, 2008;Wang & Bilek, 2011Todd et al, 2018;Passarelli et al, 2022). Seamounts likely act as a barrier to rupture propagation due to a fracture network forming in the upper plate, which decreases seismic coupling and increases creep (Wang & Bilek, 2011.…”

Observing the full ocean volume using Deep Argo floats

“…Ocean bathymetry has a fundamental impact on the pathway and strength of ocean currents (Wilson et al, 2022), and amplitude of ocean mixing (Mashayek et al, 2017), and can influence heat and freshwater exchange between the ocean and atmosphere (de Boer et al, 2022). Variations in the shape of the seafloor can dictate the magnitude and frequency of earthquakes (Passarelli et al, 2022) and the generation and propagation of tsunamis (Salaree and Okal, 2020). Less than 24% of the seafloor topography from the General Bathymetric Chart of the Ocean (GEBCO) dataset is constrained by shipboard sounding measurements or other direct measurements, and is limited mostly to Exclusive Economic Zones (Tozer et al, 2019;Wölfl et al, 2019;GEBCO Bathymetric Compilation Group, 2022).…”