Earthquake rupture below the brittle-ductile transition in continental lithospheric mantle

• Published in: Science Advances
• Main Authors: Prieto, Germán A., Froment, Bérénice, Yu, Chunquan, Poli, Piero, Abercrombie, Rachel
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Association for the Advancement of Science 2017
• Subjects: continental lithosphere; rheology; earthquake sources; directivity; lithosphere; rupture mechanics; Molnar; Hager; Seismological Facilities for the Advancement of Geoscience and EarthScope
• Online Access: https://doi.org/10.1126/sciadv.1602642; https://www.ncbi.nlm.nih.gov/pmc/PMC5351985

Earthquakes deep in the continental lithosphere are rare and hard to interpret in our current understanding of temperature control on brittle failure. The recent lithospheric mantle earthquake with a moment magnitude of 4.8 at a depth of ~75 km in the Wyoming Craton was exceptionally well recorded and thus enabled us to probe the cause of these unusual earthquakes. On the basis of complete earthquake energy balance estimates using broadband waveforms and temperature estimates using surface heat flow and shear wave velocities, we argue that this earthquake occurred in response to ductile deformation at temperatures above 750°C. The high stress drop, low rupture velocity, and low radiation efficiency are all consistent with a dissipative mechanism. Our results imply that earthquake nucleation in the lithospheric mantle is not exclusively limited to the brittle regime; weakening mechanisms in the ductile regime can allow earthquakes to initiate and propagate. This finding has significant implications for understanding deep earthquake rupture mechanics and rheology of the continental lithosphere. © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. Distributed under a Creative Commons Attribution Noncommercial License 4.0 (CC BY-NC). Submitted 26 October 2016; Accepted 3 February 2017; Published 15 March 2017. We thank W. P. Chen, P. Molnar, B. Hager, B. Schmandt, G. Beroza, and anonymous reviewers for fruitful discussions. We acknowledge U. Faul for help in temperature modeling. Funding: G.A.P. and P.P. was supported by the NSF (grant EAR-1521534). Incorporated Research Institutions for Seismology (IRIS) Data Services were funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope proposal under the NSF cooperative agreement (EAR-1261681). Author contributions: G.A.P., B.F., R.A., and P.P. designed the study and processed the data. C.Y. and G.A.P. developed the temperature modeling. All authors discussed the results ...