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The primary use of the natural hazards data archived at the National Geophysical Data Center (NGDC) and co-located World Data Center for Solid Earth Geophysics (WDC for SEG) is for the mitigation of future disasters. Among the responsibilities of NGDC/WDC for SEG is archiving and disseminating hazards data to city planners, educators, engineers and others engaged in mitigation efforts (approximately 150,000 users per week on our web site). Therefore, it is the purpose of this paper to educate the hazards' community about some of the limitations of these data. It is hoped that enlightened users would have a greater appreciation of data errors and possible sources of misinterpretation of the data. Personnel at NGDC/WDC for SEG are in a unique position to discuss the limitations of hazards data since we compile data from original and secondary sources. We are also in direct contact with the data users and know the applications that they make of hazard data, and the misjudgments that often occur when data limitations are not known. Most hazard catalogs cover periods of less than 200 years and are reasonably complete and accurate for only the past 20 to 50 years. Such catalogs are not sufficient to investigate long term hazard variations. Earthquake, tsunami, and volcano data catalogs, acquired and integrated at NGDC/WDC for SEG, illustrate artificial long-term variations created by cultural and scientific reporting changes, which can introduce unanticipated non-random variations into the catalogs. Inconsistencies are often related to changes in the way magnitudes are calculated, evolving network equipment, and network discontinuities of operation and personnel, among other error sources. Before statistical hazard studies can be done, catalogs need to be clearly understood to identify systematic patterns of an observational nature. |
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