Earthquake nucleation in the lower crust by local stress amplification

Campbell, L. R.; Menegon, L.; Fagereng, Å.; Pennacchioni, G.

Abstract

Deep intracontinental earthquakes are poorly understood, despite their potential to cause significant destruction. Although lower crustal strength is currently a topic of debate, dry lower continental crust may be strong under high-grade conditions. Such strength could enable earthquake slip at high differential stress within a predominantly viscous regime, but requires further documentation in nature. Here, we analyse geological observations of seismic structures in exhumed lower crustal rocks. A granulite facies shear zone network dissects an anorthosite intrusion in Lofoten, northern Norway, and separates relatively undeformed, microcracked blocks of anorthosite. In these blocks, pristine pseudotachylytes decorate fault sets that link adjacent or intersecting shear zones. These fossil seismogenic faults are rarely >15 m in length, yet record single-event displacements of tens of centimetres, a slip/length ratio that implies >1 GPa stress drops. These pseudotachylytes represent direct identification of earthquake nucleation as a transient consequence of ongoing, localised aseismic creep.

Citation

Campbell, L. R., Menegon, L., Fagereng, Å., & Pennacchioni, G. (2020). Earthquake nucleation in the lower crust by local stress amplification. Nature communications, 11(1), Article 1322. https://doi.org/10.1038/s41467-020-15150-x

• Journal Article Type: Article
• Acceptance Date: Feb 14, 2020
• Online Publication Date: Mar 12, 2020
• Publication Date: 2020-12
• Deposit Date: Apr 3, 2022
• Publicly Available Date: Apr 4, 2022
• Journal: Nature Communications
• Publisher: Nature Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 11
• Issue: 1
• Article Number: 1322
• DOI: https://doi.org/10.1038/s41467-020-15150-x
• Keywords: Geophysics; Seismology; Structural geology; Tectonics
• Public URL: https://hull-repository.worktribe.com/output/3752761