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Resolving northern Alaska earthquake sequences using the transportable array and probabilistic location methods

Steven J. Gibbons, Natalia A. Ruppert, Ezgi Karasozen, Kasey Aderhold and Ian Dickson
Resolving northern Alaska earthquake sequences using the transportable array and probabilistic location methods
Seismological Research Letters (July 2020) Pre-Issue Publication


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.

ISSN: 0895-0695
EISSN: 1938-2057
Serial Title: Seismological Research Letters
Serial Volume: Pre-Issue Publication
Title: Resolving northern Alaska earthquake sequences using the transportable array and probabilistic location methods
Affiliation: Norges Geotekniske Institutt, Oslo, Norway
Published: 20200722
Text Language: English
Publisher: Seismological Society of America, El Cerrito, CA, United States
References: 45
Accession Number: 2020-079373
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps
N67°00'00" - N71°00'00", W148°00'00" - W144°00'00"
Secondary Affiliation: University of Alaska Fairbanks, USA, United StatesKasey Aderhold, USA, United StatesUniversity of Colorado, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202022
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