The Influence of Depth‐Varying Elastic Properties of the Upper Plate on Megathrust Earthquake Rupture Dynamics and Tsunamigenesis

Abstract

Megathrust earthquakes nucleate within the seismogenic zone (Byrne et al., 1988;Hyndman et al., 1997). The updip limit of this region may vary depending on material properties and thermal conditions along the megathrust (Hyndman et al., 1997), but it is commonly defined between 5 and 10 km depth (Scholz, 1998). Yet, megathrust earthquakes may occasionally rupture through the shallow and apparently aseismic region of the fault (<5 km of depth), particularly in areas with sediment-starved trenches and irregular subducting

The 2021 South Sandwich Island Mw 8.2 Earthquake: A Slow Event Sandwiched Between Regular Ruptures

“…Although the shallowest subduction interface is often considered seismically inactive due to the velocity-strengthening frictional properties (Scholz, 1998), some large tsunami earthquakes were found to host major slip at near-trench depths (Kanamori & Kikuchi, 1993;Lay et al, 2011). Lower upper plate rock rigidity at shallow depths has been illustrated to produce tsunami earthquake-like properties, including depleted short period seismic energy and slow rupture (Bilek & Lay, 1999;Sallarès & Ranero, 2019;Sallares et al, 2021), which well explains our observations for E3, suggesting the subduction zone geologic conditions could largely impact the tsunami potential. However, the slow component of the South Sandwich Island earthquake may have a broader depth extent than the traditional tsunami earthquakes.…”

“…At deeper depths (15–50 km), large thrust earthquakes have faster rupture velocities and stronger radiation of short‐period seismic energy with inefficient tsunami generation. Their contrasting rupture characteristics are well interpreted by two distinct types of fault properties; the slow slip of shallow tsunami earthquakes is commonly attributed to weak sediments and low rigidity of the upper plate (Bilek & Lay, 1999; Prada et al., 2021; Sallarès & Ranero, 2019), while the brittle failures of unstable fault patches explain the fast deeper earthquakes.…”

“…At deeper depths (15-50 km), large thrust earthquakes have faster rupture velocities and stronger radiation of short-period seismic energy with inefficient tsunami generation. Their contrasting rupture characteristics are well interpreted by two distinct types of fault properties; the slow slip of shallow tsunami earthquakes is commonly attributed to weak sediments and low rigidity of the upper plate (Bilek & Lay, 1999;Prada et al, 2021;Sallarès & Ranero, 2019), while the brittle failures of unstable fault patches explain the fast deeper earthquakes.On 12 August 2021, a great earthquake (M w > 8) struck the South Sandwich Island region of the south Atlantic Ocean (Figure 1a). This event occurred close to the South Sandwich trench, where the South American plate subducts beneath the South Sandwich plate at a velocity of 7 cm/year (Pelayo & Wiens, 1989).…”

Coseismic Deformation Responses due to Geometrical Structure and Heterogeneity of the Accretionary Wedge: Study Case 2010 Mentawai Earthquake, West Sumatra, Indonesia

“…The elastic properties especially at the upper plate of subduction zone dominantly control large shallow slip and slow rupture which is related to a larger coseismic surface deformation. Incorporation realistic megathrust elastic properties and rigidity variation of the upper plate cannot be neglected and contribute to a better earthquake and tsunami hazard prediction [40].…”

A Method to Generate Initial Fault Stresses for Physics-Based Ground-Motion Prediction Consistent with Regional Seismicity

“…The effect of crustal velocity structure on dynamic rupture and source properties is increasingly recognized (e.g., Prada et al, 2021;Huang, 2021). This effect is exacerbated in our examples, because we did not include the competing effects of cohesion and frictional strengthening at shallow depth.…”