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

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2018-07, Vol.19 (7), p.2121-2146
• Main Authors: Lallemand, Serge, Peyret, Michel, Rijsingen, Elenora, Arcay, Diane, Heuret, Arnauld
• Format: Article
• Language: English
• Subjects: Amplitude; Aseismic ridges; Dynamics; Earth Sciences; Earthquakes; Fracture zones; Ocean floor; Oceanic trenches; Plate tectonics; proxy; Ridges; Roughness; Roughness parameters; rupture dynamics; Sciences of the Universe; seafloor roughness; Seamounts; Seismic activity; Spatial distribution; Subduction; subduction earthquake; subduction interface; Subduction zones; Tectonics; Trenches; Wavelength; Wavelengths
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2018GC007434

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. Plain Language Summary We have developed a new database characterizing the seafloor roughness seaward of oceanic trenches as a proxy of the roughness of the subduction interface with the aim to evaluate how it influences the occurrence of large interplate earthquakes. Counterintuitively, we observe that the coupling between the converging plates is higher when the plate interface is smooth, and the coupling is low when the interface is rough. Key Points We have developed a new database characterizing seafloor roughness seaward of oceanic subduction trenches The oceanic seafloor prior to subduction is used as a proxy of the seismogenic subduction interface Trench segments are described in terms of short‐ or long‐wavelength parameters High seismic coupling is observed when seafloor roughness is relatively low, and low seismic coupling is associated w