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Earthquake nucleation and fault slip complexity in the lower crust of central Alaska

Tape, Carl and Holtkamp, Stephen and Silwal, Vipul and Hawthorne, Jessica and Kaneko, Yoshihiro and Ampuero, Jean-Paul and Ji, Chen and Ruppert, Natalia and Smith, Kyle and West, Michael E. (2018) Earthquake nucleation and fault slip complexity in the lower crust of central Alaska. Nature Geoscience, 11 (7). pp. 536-541. ISSN 1752-0894. doi:10.1038/s41561-018-0144-2.

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Earthquakes start under conditions that are largely unknown. In laboratory analogue experiments and continuum models, earthquakes transition from slow-slipping, growing nucleation to fast-slipping rupture. In nature, earthquakes generally start abruptly, with no evidence for a nucleation process. Here we report evidence from a strike-slip fault zone in central Alaska of extended earthquake nucleation and of very-low-frequency earthquakes (VLFEs), a phenomenon previously reported only in subduction zone environments. In 2016, a VLFE transitioned into an earthquake of magnitude 3.7 and was preceded by a 12-hour-long accelerating foreshock sequence. Benefiting from 12 seismic stations deployed within 30 km of the epicentre, we identify coincident radiation of distinct high-frequency and low-frequency waves during 22 s of nucleation. The power-law temporal growth of the nucleation signal is quantitatively predicted by a model in which high-frequency waves are radiated from the vicinity of an expanding slow slip front. The observations reveal the continuity and complexity of slip processes near the bottom of the seismogenic zone of a strike-slip fault system in central Alaska.

Item Type:Article
Related URLs:
URLURL TypeDescription ReadCube access
Tape, Carl0000-0003-2804-7137
Holtkamp, Stephen0000-0002-8863-2322
Silwal, Vipul0000-0001-9699-3489
Hawthorne, Jessica0000-0002-4117-2082
Kaneko, Yoshihiro0000-0003-2342-0131
Ampuero, Jean-Paul0000-0002-4827-7987
Ji, Chen0000-0002-0350-5704
Ruppert, Natalia0000-0003-0589-1159
Smith, Kyle0000-0002-8335-4722
West, Michael E.0000-0003-4855-9295
Additional Information:© 2018 Macmillan Publishers Limited, part of Springer Nature. Received: 28 November 2017; Accepted: 30 April 2018; Published: 4 June 2018. Seismic instruments, data archiving and data access were supported by the U.S. National Science Foundation grants EAR-1352668 and EAR-1645313, the Alaska Earthquake Center, the IRIS Data Management Center and the PASSCAL Instrument Center. Y.K. was supported by Rutherford Discovery Fellowship from the Royal Society of New Zealand. Author Contributions: All authors contributed to the manuscript. C.T., S.H. and V.S. performed the seismological analyses of the two events. J.H. performed the phase coherence analysis (Fig. 3). Y.K., J.P.A. and J.H. contributed the rate-and-state modelling and interpretation. C.J. performed the source time function estimation. C.T., N.R., K.S. and M.E.W. were responsible for the deployment of FLATS seismic stations. N.R. and S.H. discovered the high-frequency and low-frequency signals for the 2015 event. S.H. discovered the low-frequency foreshock (VLFE) of the 2016 event. Data availability: All seismic data used in this study, notably from the FLATS (XV) seismic network (, are publicly available from the IRIS Data Management Center ( Expanded results of moment tensor inversions are available in ref. 56. The authors declare no competing interests.
Funding AgencyGrant Number
Alaska Earthquake CenterUNSPECIFIED
IRIS Data Management CenterUNSPECIFIED
Royal Society of New ZealandUNSPECIFIED
Issue or Number:7
Record Number:CaltechAUTHORS:20180405-134047605
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85647
Deposited By: George Porter
Deposited On:08 Jun 2018 16:24
Last Modified:15 Nov 2021 20:30

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