What Controls Maximum Magnitudes of Giant Subduction Earthquakes?

Iskander A Muldashev,Stephan V Sobolev

doi:10.1029/2020gc009145

Iskander A Muldashev, Stephan V Sobolev

Open Access

https://doi.org/10.1029/2020gc009145

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Abstract

AbstractGiant earthquakes with magnitudes above 8.5 occur only in subduction zones. Despite the developments made in observing large subduction zone earthquakes with geophysical instruments, the factors controlling the maximum size of these earthquakes are still poorly understood. Previous studies have suggested the importance of slab shape, roughness of the plate interface contact, state of the strain in the upper plate, thickness of sediments filling the trenches, and subduction rate. Here, we present 2‐D cross‐scale numerical models of seismic cycles for subduction zones with various geometries, subduction channel friction configurations, and subduction rates. We found that low‐angle subduction and thick sediments in the subduction channel are the necessary conditions for generating giant earthquakes, while the subduction rate has a negligible effect. We suggest that these key parameters determine the maximum magnitude of a subduction earthquake by controlling the seismogenic zone width and smoothness of the subduction interface. This interpretation supports previous studies that are based upon observations and scaling laws. Our modeling results also suggest that low static friction in the sediment‐filled subduction channel results in neutral or moderate compressive deformation in the overriding plate for low‐angle subduction zones hosting giant earthquakes. These modeling results agree well with observations for the largest earthquakes. Based on our models we predict maximum magnitudes of subduction earthquakes worldwide, demonstrating the fit to magnitudes of all giant earthquakes of the 20th and 21st centuries and good agreement with the predictions based on statistical analyses of observations.

Highlights

Introduction and Key ObservationsThere are different hypotheses about the role of subduction zone parameters in producing giant earthquakes (GEQs)
We found that low‐angle subduction and thick sediments in the subduction channel are the necessary conditions for generating giant earthquakes, while the subduction rate has a negligible effect
The seismic moments are larger in subduction zones with lower effective friction coefficients

Summary

Introduction

Introduction and Key ObservationsThere are different hypotheses about the role of subduction zone parameters in producing giant earthquakes (GEQs). Based on observations available in the 1970s, Kelleher et al (1974) proposed that the key factor controlling the magnitude of events is the width of the seismogenic zone They suggested that slabs dipping with low angles have a larger contact area with the overriding plates, which allows for the occurrence of GEQs. Later, Ruff and Kanamori (1980) proposed that the maximum magnitude of an earthquake is controlled by two parameters: the age of the subducting plate and the plate convergence rate. The view by Ruff and Kanamori (1980) became the “classical” one until the suggested correlation was violated by a number of GEQs such as the two largest earthquakes of the 21st century, the Great Sumatra/Andaman 2004 earthquake and the Tohoku 2011 earthquake (Heuret et al, 2011)

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