Initial Impact of the Global Seismographic Network Quality Initiative on Metadata Accuracy

The IRIS/USGS Global Seismographic Network (Butler et al. , 2004) is used to investigate earth structure at multiple scales, to capture information about massive earthquakes impossible to obtain at regional scales, and to characterize seismicity in regions of the world where instrument coverage is poor. A key design goal of the GSN, to place high performance instruments at 2,000 km spacing around the planet, has largely been achieved except for portions of the ocean basins. Several agencies, including the USGS National Earthquake Information Center, the NOAA Tsunami Warning Centers, and the United Nations Comprehensive Test Ban Treaty Organization, now utilize GSN seismic data to accomplish their missions. Those who use GSN data rely upon the accuracy of the metadata provided to them through the IRIS’ Data Management System (DMS). The DMS in turn distributes response information supplied by the GSN network operators, the USGS Albuquerque Seismic Laboratory (ASL) and the University of California, San Diego’s Project IDA (IDA). Improved metadata will aid researchers who seek to model earth structure in greater detail as well as those who seek to characterize seismic sources at varying scales. The GSN’s operators continually assess engineering information to ensure that waveform quality is maximized and that published metadata accurately reflect the instrument response of the data acquisition systems (DASs). A detailed description of those operational procedures currently used to accomplish these goals can be found at the IRIS GSN Quality web page (http://www.iris.edu/hq/programs/gsn/quality). One important element of this effort is the practice of colocating a portable, broadband seismometer in proximity to GSN sensors during field-maintenance visits to verify the in situ sensors’ calibration and orientation. The calibration of this portable sensor is measured in the laboratory. Without this additional experimental evidence, the validity of comparing the outputs of permanent and temporary sensors and also …