Roughness Characteristics of Oceanic Seafloor Prior to Subduction in Relation to the Seismogenic Potential of Subduction Zones

Abstract

We have developed a new approach to characterize the seafloor roughness seaward of the trenches, as a proxy for estimating the roughness of the subduction interface. We consider that abrupt elevation changes over given wavelengths play a larger role in the seismogenic behavior of the subduction interface than the amplitude of bathymetric variations alone. The new database, SubRough, provides roughness parameters at selected spatial wavelengths. Here we mainly discuss the spatial distribution of short‐ (12–20 km) and long‐wavelength (80–100 km) roughness, RSW and RLW, respectively, along 250‐km‐wide strips of seafloor seaward of the trenches. Compared with global trend, seamounts show distinct roughness signature of much larger amplitudes at both wavelengths, whereas aseismic ridges only differ from the global trend at long wavelengths. Fracture zones cannot be distinguished from the global trend, which suggests that their potential effect on rupture dynamics is not the consequence of their roughness, at least not at these wavelengths. Based on RLW amplitude, segments along subduction zones can be defined from rough to smooth. Subduction zones like the Solomons or the Ryukyus appear dominantly rough, whereas others like the Andes or Cascadia are dominantly smooth. The relative contribution of smooth versus rough areas in terms of respective lateral extents probably plays a role in multipatch rupture and thus in the final earthquake magnitude. We observe a clear correlation between high seismic coupling and relatively low roughness and conversely between low seismic coupling and relatively high seafloor roughness.

How Subduction Interface Roughness Influences the Occurrence of Large Interplate Earthquakes

“…Individual figures for all subduction zones in Table 2 can be found in Figures S2 to S16 in the supporting information. As can be seen in Figure 7, all the subduction zones with RLR > 50% face mainly smooth to moderately rough seafloor, as shown in Figure 5 and demonstrated as well by Lallemand et al (2018). Figure 8 shows density distributions for the long-wavelength roughness signal of the subduction zones displayed in Figures 6 and 7, illustrating which roughness amplitudes are the most common for these regions.…”

“…Finally, we discuss our main findings by looking at how they relate to the results and concepts previously published. the trench, presented by Lallemand et al (2018). They have developed an approach to estimate the roughness signal at different spatial wavelengths to characterize the seafloor bathymetry prior to subduction, to be used as a proxy for the roughness of the subduction interface (Figure 1).…”

Rough Subducting Seafloor Reduces Interseismic Coupling and Mega‐Earthquake Occurrence: Insights From Analogue Models

“…Global studies have shown that large earthquakes (M W ≥ 7.5) preferably occur along a smooth subduction interface and that rough subducting seafloor is associated with lower seismic coupling and a creep-like behavior (Bassett & Watts, 2015;Lallemand et al, 2018;van Rijsingen et al, 2018;Wang & Bilek, 2014). Global studies have shown that large earthquakes (M W ≥ 7.5) preferably occur along a smooth subduction interface and that rough subducting seafloor is associated with lower seismic coupling and a creep-like behavior (Bassett & Watts, 2015;Lallemand et al, 2018;van Rijsingen et al, 2018;Wang & Bilek, 2014).…”

Coupled Evolution of Deformation, Pore Fluid Pressure, and Fluid Flow in Shallow Subduction Forearcs

“…A number of studies have suggested that subducting basement relief strongly affects megathrust stress state and slip behavior (Das & Watts, 2009; Lallemand et al, 2018; van Rijsingen et al, 2018; Wang & Bilek, 2011, 2014), the rupture dynamics of subduction earthquakes (Kodaira et al, 2000; Lay, 2015; Nakatani et al, 2015; Ye et al, 2016, 2018), and long‐term margin evolution and mass transport as governed by subduction erosion and accretion (Bassett & Watts, 2015; Kopp, 2013; von Huene et al, 2004; von Huene & Scholl, 1991). The overall conceptual picture is one of a structurally disrupted upper plate, a highly heterogeneous stress state, pervasive shearing and fracturing promoted by the irregular geometry, and spatially complex patterns of basal erosion and material underplating.…”

“…Also, sediment thickness on the incoming plate differs drastically among subduction zones, ranging from less than 1 km for almost 50% of subduction zones globally, to over 7 km for sediment‐rich subduction zones such as Makran and the Southern Antilles (Scholl et al, 2015). Geomorphological observations indicate spatially variable roughness of subducting seafloor at different subduction margins (Kopp, 2013; Lallemand et al, 2018; Ryan et al, 2009). Field and laboratory observations have also documented variations in other parameters, including plate convergence rate (DeMets et al, 2010), slab dip angle (Hayes et al, 2018), and subduction décollement strength (Ikari, 2019; Ikari & Kopf, 2017).…”