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Magnetic field variations in Alaska; recording space weather events on seismic stations in Alaska

Adam T. Ringler, Robert E. Anthony, David C. Wilson, Abram C. Claycomb and John Spritzer
Magnetic field variations in Alaska; recording space weather events on seismic stations in Alaska
Bulletin of the Seismological Society of America (June 2020) Pre-Issue Publication

Abstract

Seismometers are highly sensitive instruments to not only ground motion but also many other nonseismic noise sources (e.g., temperature, pressure, and magnetic field variations). We show that the Alaska component of the Transportable Array is particularly susceptible to recording magnetic storms and other space weather events because the sensors used in this network are unshielded and magnetic flux variations are stronger at higher latitudes. We also show that vertical-component seismic records across Alaska are directly recording magnetic field variations between 40 and 800 s period as opposed to actual ground motion during geomagnetic events with sensitivities ranging from 0.004 to 0.48 (m/s (super 2) )/T. These sensitivities were found on a day where the root mean square variation in the magnetic field was 225 nT. Using a method developed by Forbriger (2007, his section 3.1), we show that improving vertical seismic resolution of an unshielded sensor by as much as 10 dB in the 100-400 s period band using magnetic data from a collocated three-component magnetometer is possible. However, due to large spatial variations in Earth's magnetic field, this methodology becomes increasingly ineffective as the distance between the seismometer and magnetometer increases (no more than 200 km separation). A potential solution to this issue may be to incorporate relatively low-cost magnetometers as an additional environmental data stream at high-latitude seismic stations. We demonstrate that the Bartington Mag-690 sensors currently deployed at Global Seismographic Network sites are not only acceptable for performing corrections to seismic data, but are also capable of recording many magnetic field signals with similar signal-to-noise ratios, in the 20-1000 s period band, as the observatory grade magnetometers operated by the U.S. Geological Survey Geomagnetism Program. This approach would densify magnetic field observations and could also contribute to space weather monitoring by supplementing highly calibrated magnetometers with additional sensors.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: Pre-Issue Publication
Title: Magnetic field variations in Alaska; recording space weather events on seismic stations in Alaska
Affiliation: U. S. Geological Survey, Albuquerque, NM, United States
Published: 20200630
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 43
Accession Number: 2020-060722
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch map
N51°00'00" - N72°00'00", W130°00'00" - E173°00'00"
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: 202017
Program Name: USGSOPNon-USGS publications with USGS authors
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