Earthquake stress-drop values delineate spatial variations in maximum shear stress in the Japanese forearc lithosphere
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Abstract
Earthquake stress drop (Δσ) may increase with depth and stress in the brittle lithosphere. However, the range of uncertainty in Δσ and the lack of constraints on absolute stress make it difficult to establish whether they are correlated. Here, we investigate Δσ dependence on depth and maximum shear stress (τmax) based on ~11 years of seismicity in the northeastern Japanese forearc following the 2011 Tohoku-Oki megathrust earthquake. We interpret Δσ estimates computed using both individual spectra and spectral-ratio methods and find that Δσ exhibits a clear depth dependence within the seismically active upper ~60 km of the forearc lithosphere ( ~ 0.8 MPa per 10 km). We further compare Δσ values with quantitative τmax estimates from finite-element models of force balance. We find that median Δσ values increase with τmax in the brittle forearc lithosphere and that earthquake stress release is proportional to τmax. The dependence of Δσ on τmax explains the apparent depth dependence of Δσ and suggests that average Δσ values provide a relative measure of the stress at failure. In the northeastern Japanese forearc, Δσ values remained roughly constant in the decade following the Tohoku-Oki earthquake, suggesting negligible changes in failure stress in the forearc since the mainshock.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Earthquake stress-drop values delineate spatial variations in maximum shear stress in the Japanese forearc lithosphere |
| Series title | Communications Earth and Environment |
| DOI | 10.1038/s43247-025-02877-y |
| Volume | 6 |
| Publication Date | October 29, 2025 |
| Year Published | 2025 |
| Language | English |
| Publisher | Springer Nature |
| Contributing office(s) | Earthquake Science Center |
| Description | 858, 14 p. |
| Country | Japan |