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Earthquake nucleation in the lower crust by local stress amplification

Campbell, L. R., Menegon, L., Fagereng, Å. and Pennacchioni, G. 2020. Earthquake nucleation in the lower crust by local stress amplification. Nature Communications 11 (1) , 1322. 10.1038/s41467-020-15150-x

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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.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Earth and Ocean Sciences
Publisher: Nature Research
ISSN: 2041-1723
Date of First Compliant Deposit: 12 March 2020
Date of Acceptance: 14 February 2020
Last Modified: 13 Mar 2020 11:30
URI: http://orca.cf.ac.uk/id/eprint/130382

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