Dense lower crust elevates long-term earthquake rates in the New Madrid seismic zone

Geophysical Research Letters
By: , and 

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Abstract

Knowledge of the local state of stress is critical in appraising intraplate seismic hazard. Inverting earthquake moment tensors, we demonstrate that principal stress directions in the New Madrid seismic zone (NMSZ) differ significantly from those in the surrounding region. Faults in the NMSZ that are incompatible with slip in the regional stress field are favorably oriented relative to local stress. We jointly analyze seismic velocity, gravity, and topography to develop a 3-D crustal and upper mantle density model, revealing uniquely dense lower crust beneath the NMSZ. Finite element simulations then estimate the stress tensor due to gravitational body forces, which sums with regional stress. The anomalous lower crust both elevates gravity-derived stress at seismogenic depths in the NMSZ and rotates it to interfere more constructively with far-field stress, producing a regionally maximal deviatoric stress coincident with the highest concentration of modern seismicity. Moreover, predicted principal stress directions mirror variations (observed independently in moment tensors) at the NMSZ and across the region.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Dense lower crust elevates long-term earthquake rates in the New Madrid seismic zone
Series title Geophysical Research Letters
DOI 10.1002/2016GL070175
Volume 43
Issue 16
Year Published 2016
Language English
Publisher American Geophysical Union
Publisher location Washington, D.C.
Contributing office(s) Geologic Hazards Science Center
Description 12 p.
First page 8499
Last page 8510
Country United States
State Arkansas, Missouri, Tennessee