The tables and figures in this electronic supplement complement the selections in the paper, either illustrating additional components, additional noise analysis, or other stations.
Table S1. Locations and geology of China Digital Seismograph Network (CDSN) and New China Digital Seismograph Network (NCDSN) stations. Station BJI (Baijiatuan, Beijing, China) was relocated to BJT (Baijiatuan, Beijing, China) in 1994; the equipment at MDJ (Mudanjiang, Heilongjiang Province, China) was relocated to a new tunnel at the same site in 2013 but at a higher elevation. Site geology is from Zhou et al. (2005).
Table S2. History of instrumentation at CDSN/NCDSN sites. The secondary sensor models were initially short-period sensors but were replaced by broadband sensors. (DAS, data acquisition system)
Table S3. Year of first observed degradation of the long-period response of the STS-1 seismometers at CDSN/NCDSN stations, as observed in the vertical (LHZ), north (LHN), and east (LHE) channels. No significant degradation was observed at station KMI (Kunming, Yunnan Province, China), MDJ (Mudanjiang, Heilongjiang Province, China), or WMQ (Urumqi, Xinjiang Province, China).
Table S4. Data streams transmitted from the NCDSN stations following the 2013 upgrade. As part of the upgrade, the names of the horizontal channels were changed from N and E to 1 and 2. Thus, LHN became LH1, and LHE became LH2.
Table S5. Results from the verification of orientation and gain at the CDSN/NCDSN sites prior to the 2013 upgrades. Location codes for the orientation corrections are 00 for the primary sensor and 10 for the secondary sensor. These corrections have been made to the metadata, and the dataless SEED volumes have been updated.
Figure S1. Comparison between data and synthetic seismograms for earthquakes in the Sea of Okhotsk (a) before the upgrades (Mw 7.7 8/14/2012) and (b) after the upgrades (Mw 8.8 5/24/2013). For each station channel, the synthetic is in solid black, the primary sensor data is in light gray dashes (location code 00), and the secondary sensor data is in light gray dots (location code 10). The north-component waveforms have been deconvolved to displacement and bandpass filtered between 100 and 400 s. Stations KMI and WMQ were down during the 8/14/2012 event. The comparison for the vertical component is shown in Figure 5 in the main article.
Figure S2. Comparison between data and synthetic seismograms for earthquakes in the Sea of Okhotsk (a) before the upgrades (Mw 7.7 8/14/2012) and (b) after the upgrades (Mw 8.8 5/24/2013). For each station channel, the synthetic is in solid black, the primary sensor data is in light gray dashes (location code 00), and the secondary sensor data is in light gray dots (location code 10). The east-component waveforms have been deconvolved to displacement and bandpass filtered between 100 and 400 s. Stations KMI and WMQ were down during the 8/14/2012 event. The comparison for the vertical component is shown in Figure 5 in the main article.
Figure S3. The 10th percentile noise levels at the China Digital Seismograph Network/New China Digital Seismograph Network (CDSN/NCDSN) stations after the 2013 upgrade. Median estimates of the power spectral density from (a) the 00 LHZ, (b) 00 LH1, and (c) 00 LH2 STS-1 channels. The new low-noise model (NLNM; Peterson, 1993) is plotted in black. The median noise level is shown in Figure 6 in the main article.
Figure S4. The 90th percentile noise levels at the CDSN/NCDSN stations after the 2013 upgrade. Median estimates of the power spectral density from (a) the 00 LHZ, (b) 00 LH1, and (c) 00 LH2 STS-1 channels. The new low-noise model (NLNM; Peterson, 1993) is plotted in black. The median noise level is shown in Figure 6 in the main article.
Figure S5. Coherence between the primary and secondary sensor at station BJT (Baijiatuan, Beijing, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions. This figure shows the coherence since the upgrade, when the Geotech GS-13 was replaced with an STS-2.5.
Figure S6. Coherence between the primary and secondary sensor at station ENH (Enshi, Hubei Province, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions.
Figure S7. Coherence between the primary and secondary sensor at station HIA (Hailar, Neimenggu Autonomous Region, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions. This figure shows the coherence since the upgrade, when the Geotech GS-13 was replaced with an STS-2.5.
Figure S8. Coherence between the primary and secondary sensor at station KMI (Kunming, Yunnan Province, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions.
Figure S9. Coherence between the primary and secondary sensor at station LSA (Tibet, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions.
Figure S10. Coherence between the primary and secondary sensor at station MDJ (Mudanjiang, Heilongjiang Province, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions.
Figure S11. Coherence between the primary and secondary sensor at station QIZ (Qiongzhong, Hainan Province, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions.
Figure S12. Coherence between the primary and secondary sensor at station WMQ (Urumqi, Xinjiang Province, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions.
Figure S13. Coherence between the primary and secondary sensor at station XAN (Xi’an, China) in a 90–110 s period band for the vertical (dark gray circles), the north–south (light gray squares), and the east–west (black diamonds) directions.
Figure S14. Comparison among collocated sensors at the NCDSN (New China Digital Seismograph Network) for the 12 February 2014 event in western China. In this figure, the waveforms from the STS-1, STS-2.5, and Kinemetrics EpiSensor ES-T have been deconvolved to displacement and bandpass filtered between 4 and 20 s; the horizontal channels have been rotated into (a) north and (b) east components. The agreement between the three sensors is quite good, except for a few Kinemetrics EpiSensor ES-T channels with elevated noise levels, such as the north component of station QIZ (Qiongzhong, Hainan Province, China).
Petersen, J. (1993). Observations and modeling of seismic background noise, U.S. Geological Survey Open-File Rept. 93-322, 94 pp.
Zhou, G., B. Zhang, Z. Wu, W. Huang, H. Wang, M. Li, D. He, and C. Hao (2005). CDSN: Present status and future development, Acta Sesimol. Sinica, 18, no. 1, 131–121.
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