Uncertainty estimates in broadband seismometer sensitivities using microseisms
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The midband sensitivity of a seismic instrument is one of the fundamental parameters used in published station metadata. Any errors in this value can compromise amplitude estimates in otherwise high-quality data. To estimate an upper bound in the uncertainty of the midband sensitivity for modern broadband instruments, we compare daily microseism (4- to 8-s period) amplitude ratios between the vertical components of colocated broadband sensors across the IRIS/USGS (network code IU) seismic network. We find that the mean of the 145,972 daily ratios used between 2002 and 2013 is 0.9895 with a standard deviation of 0.0231. This suggests that the ratio between instruments shows a small bias and considerable scatter. We also find that these ratios follow a standard normal distribution (R 2 = 0.95442), which suggests that the midband sensitivity of an instrument has an error of no greater than ±6 % with a 99 % confidence interval. This gives an upper bound on the precision to which we know the sensitivity of a fielded instrument.
KeywordsSeismic instrumentation Network quality Microseisms Broadband seismometers
We thank Luciana Astiz, Thomas Braun, Hunter Knox, Jill McCarthy, Janet Slate, Valerie Thomas, and two anonymous reviewers for their helpful reviews that ultimately improved the content and presentation of this manuscript. We also thank Tom VanZandt for useful discussions regarding some of the phenomena related to linear drift.
The Global Seismographic Network (GSN) is a cooperative scientific facility operated jointly by the Incorporated Research Institutions for Seismology (IRIS), the U.S. Geological Survey (USGS), and the National Science Foundation (NSF). Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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