Evidence for Deeply Subducted Lower‐Plate Seamounts at the Hikurangi Subduction Margin: Implications for Seismic and Aseismic Behavior

Abstract

Seamounts are prominent seafloor features found globally at convergent margins, where their eventual subduction has been observed to have significant effect on upper plate morphology, and is predicted to influence megathrust slip behavior. While shallow subduction of partially buried seamounts has been inferred to play a role in tectonic erosion and deformation of the upper plate (e.g., Dominguez et al., 1998;Von Huene & Scholl, 1991), less is known about what happens as a seamount subducts further because of the limited resolution of geophysical methods commonly used to identify subducting seamounts. Previous studies have imaged buried seamounts at shallow stages of subduction (e.g.,

Spatial Variation of Shallow Stress Orientation Along the Hikurangi Subduction Margin: Insights From In‐Situ Borehole Image Logging

“…Basement topographic variation, such as uplifted basement blocks or seamounts, can introduce gravity and density changes within the crust creating geomechanical inhomogeneities (e.g., Bassett et al, 2022;Chow et al, 2022). Such geomechanical inhomogeneities can add horizontal compressional stress around the uplifted basement margins and extensional stress above them, changing the stress orientations (Artyushkov, 1973;Bott, 1991; (2002).…”

Strong Upper‐Plate Heterogeneity at the Hikurangi Subduction Margin (North Island, New Zealand) Imaged by Adjoint Tomography

“…Feature A (Figure 4) is also visible at depth in northern Hawke's Bay (Figure 13e), and is discussed in further detail in Chow et al. (2022).…”

“…These features are visible at both Northern and Central Hawke's Bay, providing a link between V s structure and geologic observations of crustal structure, deposition age, and sedimentary composition (Francis et al, 2004). Feature A (Figure 4) is also visible at depth in northern Hawke's Bay (Figure 13e), and is discussed in further detail in Chow et al (2022). (Edbrooke et al, 2015;Mortimer, 2004) and the final velocity models (M28) at 3 km depth.…”

“…The results for features B and C are discussed in Section 7 alongside tectonic interpretations. The point spread functions for features A, B, and E are discussed in detail in Chow et al (2022).…”

“…Visible in both V s and V p /V s along this boundary are shallow, upper-plate expressions of the two high-velocity, low-V p /V s anomalies identified as features A and B in Section 5. These are discussed in detail in Chow et al (2022).…”