32-16 Rupture Directivity and Its Influence on Coseismic Activation of Sackungen Features in the New Madrid Seismic Zone

Session: Latest Research Advances in Structural Geology and Tectonics (Posters)

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The New Madrid Seismic Zone (NMSZ) is known for M>7 earthquake sequences that occur approximately every 500 years.  Human activity and high erosion rates in the region limit the preservation of geological records, including those of the 1811–1812 events, resulting in scarce data. However, paleoseismic studies and LiDAR imagery suggest that these events triggered displacement on ridge-top extensional features, known as sackungen, along bluffs of the eastern Mississippi River Valley (Delano et al., 2018; Gold et al., 2019). Delano et al. (2018) estimated that these sackungen require ground accelerations exceeding ~0.18 g for activation. To better understand the rupture characteristics of major NMSZ-type events and their potential to trigger sackungen motion, we conducted numerical simulations to investigate how rupture directivity influences high-frequency ground motion in the region. We carried out dynamic rupture simulations to model M7-type scenarios along the Axial (strike-slip) and Reelfoot thrust faults, the two principal fault structures in the NMSZ. Ruptures were initiated at various hypocenters to examine how directivity affects ground motion and sackungen activation. Slip rates from the simulations and the regional velocity model were incorporated into a broadband ground motion simulation platform, using the stochastic finite fault method, to generate high-frequency ground motions at documented sackungen sites. Preliminary results show that Reelfoot fault ruptures produce stronger ground motion at these sites than ruptures on the Axial fault. In particular, north-to-south ruptures along the Reelfoot thrust yield peak ground accelerations exceeding the critical threshold compared to south-to-north. These preliminary findings highlight sackungen as potentially valuable indicators for constraining rupture directivity in past major earthquakes.

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

doi: 10.1130/abs/2025AM-11151

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