Observations of Magnetic Sensitivity in EarthScope Transportable Array Broadband Seismometers
Abstract
Modern force feedback seismometers use ferromagnetic metals and magnetic coils in their construction, and as a result these instruments are sensitive to magnetic fields. Possible sources include locally generated magnetism from station electronics (i.e. spinning disks and switched dc currents), variations in the regional ambient geomagnetic field (Forbriger, 2007), and secondary effects of geomagnetically induced currents (Kozlovskaya and Kozlovsky, 2012). Local sources of magnetism can be mitigated when designing a seismometer emplacement, however the larger-scale effects are unavoidable unless the instrument is specially shielded with permalloy.
In general, the sensitivity of various seismic instruments has not been widely explored, and it is especially unknown how prominent this effect may be at high latitudes where geomagnetic activity is pervasive. As such, we focus on characterizing evidence of magnetic sensitivity for stations in the EarthScope Transportable Array (TA), which encompasses 280 broadband seismometers distributed across Alaska and northwestern Canada. These include seismometers at 194 new TA stations in 2-3 meter deep steel or PVC cased postholes, as well as 86 existing stations from other networks that utilize a variety of emplacements including vaults and boreholes. The USGS operates 5 magnetic observatories in Alaska that provide direct observations of regional geomagnetic field intensities. Using these for comparison, we will examine magnetic sensitivity across the TA as a function of geomagnetic activity, seismometer type, emplacement, and geographical location. Initial results show that magnetic sensitivity during major geomagnetic events varies greatly across the array but appears somewhat dependent on the model of seismometer. Characterizing the signals related to magnetic fields can avoid misinterpreting these signals when exploring other phenomena.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S31C0522F
- Keywords:
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- 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 7240 Subduction zones;
- SEISMOLOGYDE: 7294 Seismic instruments and networks;
- SEISMOLOGY