Historical Seismograms - Evidence from the AD 2000 Izu Islands ...

THE U.S. GEOLOGICAL SURVEY’S DATABASESOF SEISMICEVENTSJ. N. TaggartU. S. Geological SurveyBox 25046, Mail Stop 967Denver Federal Center, Denver, CO 80225, USAW. H. K. Lee and K. L. MeagherMS-977, U. S. Geological SurveyMenlo Park, CA 94025, USAABSTRACTLists of seismic events are now on databases at the U.S. Geological Survey’sNational Earthquake Information Center in Golden, Colorado, andin Menlo Park, California. These controlled-access computer files describethe location, size, focal characteristics, and effects of earthquakesand large explosions. Some also refer to sources of information, point toassociated observations, estimate parametric uncertainties and indicatethe precision of the data. The databases thus make it easy to access largequantities of data for many purposes. For example, various databaseparameters are used to plot seismicity maps, delineate active faults andaftershock zones, evaluate the probabilities of earthquake recurrence, evaluatethe rate at which regional strain energy is released, compare the publishedhypocenters of different agencies, compare estimates of magnitudesor seismic moments, plot focal mechanisms, and evaluate regional stresspatterns.The databases are organized into lists of global, national, regional andlocal earthquake events. The global, regional, and local event lists arearchived with associated observational data for future research applications.Each database comes with interactive computer codes that promptthe user to select the type, range, and output format of the data. Otherinteractive codes are used by database administrators to add, modify, ordelete individual event listings, and to sort, merge, correct, or tag duplicateevent listings among the entire contents of the database. Thus,the databases are not static, but are continually modified when new databecome available.1. IntroductionDuring the past century, scientists and lay observers have recorded nearly 1 millionearthquakes throughout the world. The quantity of data on seismic eventsis staggering, even discounting the several hundred thousand microeart hquakesrecorded locally or regionally that are included in this total. Seismologists of theU.S. Geological Survey (USGS) have developed computer databases that list mostof these seismic events so that they can be studied efficiently - a necessity for furtherresearch. The databases are on computers at the National Earthquake Informationcenter (NEIC) in Golden, Colorado, and in Menlo Park, California.Historical Seismogramsand Earthquakes of the World142