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Long-term Erosion as a Catalyst of Shallow Seismicity in Stable Continental Regions – a Global View

Description: 

The causes of seismicity and present-day deformation in Stable Continental Regions (SCRs) remain an open scientific question. Numerous driving mechanisms and local conditions may be at play, from steady-state far-field plate tectonic stresses to transient effects associated with Late Pleistocene glaciations, or structural weakening from tectonic inheritance. Here, we study the effects of long-term erosion on crustal stresses and the potential promotion of seismicity in SCRs. A theoretical analysis is performed using 2D numerical mechanical models of SCR lithosphere of various rheological properties subjected to a variety of steady-state localized erosion rates over 1 – 10 Myr. Predicted crustal stresses vary depending on geotherms, lithologies and erosion rates, but all models show a common pattern of horizontal tension in the upper crust (0 – 10 km depth) of up to a few 10s of MPa over a few Myr. A simple Mohr-Coulomb analysis shows that these erosion-driven stress perturbations can promote seismicity of all faulting styles (normal, strike-slip, reverse) in SCRs associated with very low reliefs and mostly homogeneous erosion rates, such as Western Australia or central North America. In other settings associated with more complex topography and erosion patterns, geometrical relationships between background stresses and erosion-driven stresses must be considered. We show a few examples, including the western Alps and the Appalachian Mountains, where long-term erosion rates promote local seismicity and its specific faulting style. In some cases, erosion may even be the overarching cause of the local upper crust stress field and seismicity. Because the lithosphere response to long-term localized erosion is close to that of an elastic plate, the maximum stress perturbations are focussed in the uppermost crust (ca. 0 – 5 km depth). This effect may thus provide an explanation for the tendency of SCRs earthquakes to concentrate at very shallow depths, as observed in large events but also increasingly in small-magnitude background seismicity.

Session: Earthquakes, Lithospheric Structure, and Dynamics in Stable Continental Region - II

Type: Oral

Date: 4/17/2025

Presentation Time: 11:00 AM (local time)

Presenting Author: Stephane

Student Presenter: No

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