169-3 Contributions to Seismicity in Stable Plate Interiors from Straining due to Plate Motion over a Non-Spherical Earth

Session: Advances and Challenges in Seismotectonic Studies in Slow-Deforming Regions

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Abstract:

The rigid-plate hypothesis, a cornerstone of plate tectonics, has long been acknowledged as a useful but incomplete approximation. Plate interiors are not perfectly rigid—while strain rates within them are significantly lower than those near plate boundaries, they can still accumulate substantial deformation and sufficient elastic strain to generate large, destructive earthquakes.

In much of the continental US, seismic hazards are dominated by these comparatively elusive earthquakes occurring in stable continental regions, which are characterized by low associated strain rates, minimal surface expression, and unpredictable recurrence intervals—factors which complicate the task of characterizing seismic hazards using observations alone. Focusing instead on strain-generating processes, we explore the effect of straining resulting from plate motion across varying radii of curvature. Because Earth is well approximated as an oblate spheroid, this deformation affects any section of the Earth's surface moving across latitudes, potentially producing up to 1% accumulated strain (equivalent to strain rates of 10^-4 yr^-1—or ~10^-11 s^-1—at typical plate velocities). Due to its broad geographic extent this effect may be the dominant source of strain in some stable plate interiors, where other sources are usually small. Although the phenomenon has been recognized since the 1970s and previously studied through numerical models, it has remained difficult to quantify precisely.

Here, we present a closed-form solution for the instantaneous strain rates resulting from latitudinal plate motion and map their spatial distribution in relation to seismicity and tectonic setting. We evaluate where these strains may be a significant driver of deformation and seismicity; in such regions, they may provide an approximation of seismic moment release. Incorporating these strains—either as input data or as a post-analysis check—could help analysts better characterize epistemic uncertainty in fault slip rate estimates thereby improving seismic hazard assessments in slow-deforming regions.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10217

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