Resolving Northern Alaska Earthquake Sequences Using the Transportable Array and Probabilistic Location Methods

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1785/0220200142. This is version 1 of this Preprint.

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Authors

Steven John Gibbons , Natalia Ruppert, Ezgi Karasözen, Kasey Aderhold, Ian Dickson

Abstract

Between 2014 and 2017, almost 200 new seismic stations were installed in Alaska and northwestern Canada as part of the EarthScope USArray Transportable Array. These stations currently provide an unprecedented capability for the detection and location of seismic events in regions with otherwise relatively sparse station coverage. Two interesting earthquake sequences in 2018 and 2019 in the northeastern Brooks Range were exceptionally well recorded because of this deployment. First is the aftershock sequence of the Mw 6.4 and Mw 6.0 Kaktovik earthquakes of 12 August 2018, the largest earthquakes recorded to date in the region. The second is the Niviak swarm, southwest of the Kaktovik sequence. Since July 2018, >4000 earthquakes between magnitudes 1 and 4.3 have been recorded across a region exceeding 5000 km2?. We explore how the Bayesloc probabilistic multiple seismic-event location algorithm can better resolve features of these two sequences, exploiting the large numbers of readings that the improved station coverage provides from events down to magnitudes below 2. The Bayesloc calculations consistently move events in the Kaktovik sequence a few kilometers to the northeast, providing an almost linear east-southeast-striking southern limit to the aftershock zone. Analysis of the Bayesloc joint probability distribution of corrections to travel-time predictions indicate that anomalously fast wave propagation to the southwest is likely the most significant contribution to the seismic-event mislocation. The joint relocations are more consistent with Interferometric Synthetic Aperture Radar-inferred coseismic displacement than the network location estimates. The Bayesloc relocation of the Niviak events confirms that the earthquakes are distributed between many distinct clusters of seismicity that have clearer spatial separation following the relocation. The probabilistic relocations motivate both double-difference studies to better resolve clustered seismicity at the smallest spatial scales and systematic multiple event relocation studies to calculate structure and travel-time corrections over larger scales.

DOI

https://doi.org/10.31223/X5B028

Subjects

Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Tectonics and Structure

Keywords

USArray, Bayesloc, Earthquake Location, Kaktovic, seismic networks, The Transportable Array, EarthScope

Dates

Published: 2021-03-25 03:58

License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None.

Data Availability (Reason not available):
All waveform data analyzed in this study is freely available from https://www.iris.edu/hq/. The earthquake catalog data is available from The Alaska Earthquake Center (https://earthquake.alaska.edu/). The Bayesloc software used to perform the relocations is available from (https://www-gs.llnl.gov/nuclear-threat-reduction/nuclear-explosion-monitoring/bayesloc)

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