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ABSTRACT Earthquakes generate infrasound in multiple ways. Acoustic coupling at the surface from vertical seismic velocity, termed local infrasound, is often recorded by infrasound sensors but has seen relatively little study. Over 140 infrasound stations have recently been deployed in Alaska. Most of these stations have single sensors, rather than arrays, and were originally installed as part of the EarthScope Transportable Array. The single sensor nature, paucity of ground-truth signals, and remoteness makes evaluating their data quality and utility challenging. In addition, despite notable recent advances, infrasound calibration and frequency response evaluation remains challenging, particularly for large networks and retrospective analysis of sensors already installed. Here, we examine local seismoacoustic coupling on colocated seismic and infrasound stations in Alaska. Numerous large earthquakes across the region in recent years generated considerable vertical seismic velocity and local infrasound that were recorded on colocated sensors. We build on previous work and evaluate the full infrasound station frequency response using seismoacoustic coupled waves. By employing targeted signal processing techniques, we show that a single seismometer may be sufficient for characterizing the response of an entire nearby infrasound array. We find that good low frequency (<1 Hz) infrasound station response estimates can be derived from large (Mw>7) earthquakes out to at least 1500 km. High infrasound noise levels at some stations and seismic-wave energy focused at low frequencies limit our response estimates. The response of multiple stations in Alaska is found to differ considerably from their metadata and are related to improper installation and erroneous metadata. Our method provides a robust way to remotely examine infrasound station frequency response and examine seismoacoustic coupling, which is being increasingly used in airborne infrasound observations, earthquake magnitude estimation, and other applications.
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Sensor orientation of the TMD seismic network (Thailand) from P-wave particle motions
Abstract The Thai Meteorological Department (TMD) seismic network began development in 2008. There are a total of 71 seismic stations consisting of 26 borehole stations and 45 surface stations currently installed. The three-component data from the TMD seismic network have been widely used in previous seismological studies. In a recent analysis, we have found that sensor orientation as reported in the site metadata is sometimes significantly incorrect, especially for borehole stations. In this study, we analyze P-wave polarization data from regional and teleseismic earthquakes recorded in the network to estimate the true instrument orientation relative to geographic north and compare that to station metadata. Of the 45 surface stations, we found that at present, ~ 82% are well oriented (i.e., aligned within 0–15° of true north). However, 8 sites have sensors misoriented by more than 15°, and some stations had a temporal change in sensor orientation during an upgrade to the seismic system with replacement of the sensor. We also evaluated sensor orientations for 26 TMD borehole seismic stations, from 2018 to the 2022. For many of the borehole stations, the actual sensor orientation differs significantly from the TMD metadata, especially at short-period stations. Many of those stations have sensor misorientations approaching 180°, due to errors in the ambient noise analysis calibration techniques used during installation. We have also investigated how this sensor misorientation affects previous seismic studies, such as regional moment tensor inversion of earthquakes sources and receiver function stacking. We have found that the large deviations in sensor orientation can result in erroneous results and/or large measurement errors. A cause of the orientation error for borehole sites could be a combination of strong background surface ambient seismic noise coupled with an incorrect reference instrument response.
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- Award ID(s):
- 1714892
- PAR ID:
- 10442489
- Date Published:
- Journal Name:
- Geoscience Letters
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 2196-4092
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1186/s40562-023-00278-7
