Constraint on the recurrence of great outer-rise earthquakes from seafloor bathymetry

Abstract

Great outer rise earthquakes are a tsunami hazard as they occur on steeply dipping faults (Lay et al., 2009). The largest instrumentally recorded of these events are the 1933 Sanriku Japan earthquake (M w = 8.4) and 1977 Sumba Indonesia earthquake (M w = 8.3) (Lay et al., 2009). Seafloor bathymetry (Kobayashi et al., 1998) and plate kinematics indicate a great M w ≥ 8 outer rise earthquake on the zone of the great Tohoku M w 9 event can occur at most once in 7 megathrust cycles.

The fingerprints of flexure in slab seismicity

“…1c,g), and in the process of unbending the plate would simply return to an undisturbed elastic state. The occurrence of intermediate depth seismicity, along with a range of other observations, provides a strong argument that this is not the case (Chapple & Forsyth, 1979;Goetze & Evans, 1979;Billen et al, 2003;Sleep, 2012).…”

“…Because this value greatly exceeds inferred yield stresses, inelastic deformation is expected to accommodate the large proportion of bending strains in slabs (Chapple & Forsyth, 1979), with brittle deformation dominating in the cold regions (Goetze & Evans, 1979). These predictions are supported by the observation that the cumulative strain of fault throws near the trench (Sleep, 2012), as well as the seismic moment of OBZ earthquakes (Chapple & Forsyth, 1979) are close to the total strain (rate) inferred from the change in curvature. An important consequence of inelastic deformation is the fact that the flexural stress state is often inverted with respect to the sign of the slab curvature (Engdahl & Scholz, 1977).…”

The Fingerprints of Flexure in Slab Seismicity

“…Because this value greatly exceeds inferred yield stresses, inelastic deformation is expected to accommodate the large proportion of bending strains in slabs (Chapple & Forsyth, 1979), with brittle deformation dominating in the cold regions (Goetze & Evans, 1979). These predictions are supported by the observation that the cumulative strain of fault throws near the trench (Sleep, 2012), and the seismic moment of OBZ earthquakes (Chapple & Forsyth, 1979) are close to the total strain (rate) inferred from the change in curvature. An important consequence of inelastic deformation is the fact that the flexural stress state is often inverted with respect to the sign of the slab curvature (Engdahl & Scholz, 1977).…”

“…If slabs behaved as perfectly elastic sheets, stress would vary systematically with the total curvature (e.g., Figures 1c and 1g), and in the process of unbending, the plate would simply return to an undisturbed elastic state. The occurrence of intermediate depth seismicity, along with a range of other observations, provides a strong argument that this is not the case (Billen et al., 2003; Chapple & Forsyth, 1979; Goetze & Evans, 1979; Sleep, 2012).…”

8. Earthquake sources of the Australian plate margin: revised models for the 2018 national tsunami and earthquake hazard assessments

“…Burbidge et al (2008a) include a normal fault source near the location of the 1977 Sumba earthquake with alternative maximum magnitudes of 8.5 and 9.0, but do not consider outer-rise events elsewhere. Sleep (2012) uses plate kinematics to argue that the rate of moment release for outer-rise events on a particular part of the Japan trench should be 0.45% that of the corresponding megathrust. This is in part based on an assumed maximum seismogenic depth of 30 km, which is shallower than sources models for the Sumba earthquake, with maximum depths of 50 km (Gusman et al, 2009;Lynnes & Lay, 1988), and the 1933 Sanriku earthquake, with a maximum depth of 70 km (Kanamori, 1971).…”