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Estimations of Sensor Misorientation for Broadband Seismic Stations in and around Africa

Ojo, Adebayo Oluwaseun and Zhao, Li and Wang, Xin (2019) Estimations of Sensor Misorientation for Broadband Seismic Stations in and around Africa. Seismological Research Letters, 90 (6). pp. 2188-2204. ISSN 0895-0695. https://resolver.caltech.edu/CaltechAUTHORS:20190828-080514403

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Abstract

To ensure the accuracy of future seismological studies using horizontal‐component data recorded by broadband seismic stations in Africa and environs, we investigate the sensor orientation of 1075 stations belonging to 41 seismic networks deployed in and around the African continent in the past three decades. We applied three independent waveform‐based orientation estimation methods that involve the measurement of P‐wave particle motion based on the principal component analysis, minimizing the P‐wave energy on the transverse component of motion, and measuring intermediate‐period Rayleigh‐wave arrival angles from teleseismic earthquakes. We found that 34.3%–43.5% of the stations are well oriented within 3°, 40%–48.2% have sensor misorientation values between 3° and 10°, whereas 16.5%–18% of the stations are misaligned by more than 10°, most likely true sensor misorientation. The fairly high correlation coefficients (0.71–0.93) and very small mean (−0.01°–0.06°) and median (−0.04°–0.3°) differences suggest a high consistency among the estimates from the three methods. Likewise, the comparison of our results with reported orientations in the metadata at 33 stations demonstrates the robustness of the results obtained in this study. Likewise, the increase in the cross‐correlation coefficients and reduced time shifts between the Rayleigh‐wave signals on the vertical and Hilbert‐transformed radial components when the sensor misorientation angles are corrected show the importance of this study. An investigation of the time dependence of the estimated misorientation angles over the validation period reveals that the sensor orientation remained fairly constant for most stations included in the study. The nearly 180° sensor misorientation angles obtained at some stations led to the suspicion of possible polarity reversal of the seismometer components and/or channel mislabeling that was confirmed with a network manager for two of the seismic stations. Result of this study serves as a reference for future data users and a reminder to seismic network managers to decrease the number of errors that may lead to misorientations in future deployments.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1785/0220190103DOIArticle
ORCID:
AuthorORCID
Ojo, Adebayo Oluwaseun0000-0002-8793-2008
Wang, Xin0000-0002-6180-0058
Additional Information:© 2019 Seismological Society of America. Published Online 28 August 2019. Data and Resources: All the seismic data used in this study are publicly available through the Incorporated Research Institutions for Seismology Data Management Centre (IRIS‐DMC; https://ds.iris.edu/ds/nodes/dmc/, last accessed March 2019). The Python‐based software package to estimate the geographic orientation of the horizontal components of broadband three‐component seismometers from Rayleigh‐wave arrival‐angle measurements is provided by Adrian K. Doran and Gabi Laske and can be publicly downloaded (https://igppweb.ucsd.edu/~adoran/DLOPy.html, last accessed October 2018). The Fortran code to estimate the sensor misorientation from P‐wave particle motion was developed by Fenglin Niu and can be requested from the author. Sac2000 (Goldstein et al., 2003) and Taup (Crotwell et al., 1999) softwares were used for basic seismic data processing. Most of the figures are produced with the Generic Mapping Tools (GMTs) of Wessel et al. (2013). The Standing Order for Data (SOD) program of Owens et al. (2004) was used to retrieve waveforms achieved at the IRIS‐DMC. A Python framework for processing seismological data named ObsPy (Beyreuther et al., 2010) was used to compute the probabilistic power spectral densities (PPSDs). The authors thank the participants of the AfricaArray project and other seismic network managers whose stations are included in this study for installing and maintaining their seismic array. The authors thank Ofonime U. Akpan (Centre for Geodesy and Geodynamics, Nigeria Space Research and Development Agency, Toro, Bauchi State, Nigeria) for the helpful discussions. O. A. O acknowledges the support of the Boya Postdoctoral Fellowship of Peking University. The authors are thankful to Editor‐in‐Chief Zhigang Peng and Associate Editor Brandon Schmandt for handling their article, as well as three anonymous reviewers for their constructive comments and suggestions that helped improve the quality of this article.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
Peking UniversityUNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20190828-080514403
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190828-080514403
Official Citation:Adebayo Oluwaseun Ojo, Li Zhao, Xin Wang; Estimations of Sensor Misorientation for Broadband Seismic Stations in and around Africa. Seismological Research Letters ; 90 (6): 2188–2204. doi: https://doi.org/10.1785/0220190103
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98280
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:28 Aug 2019 16:15
Last Modified:09 Mar 2020 13:19

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