Digitized Waveforms Obtained from Videotaped Pictures of Landscape Shaking during Large Earthquakes

Since the history of strong motion observation began, with the successful acquisition of acceleration records (with a maximum acceleration of 0.23 g) during the Long Beach California earthquake in 1933 (Hudson, 1984), strong-motion records have accumulated for over sixty years. However, there are not yet enough records for us to understand fully the strong ground motions caused by large earthquakes. For this reason we must depend upon traditional investigations of seismic intensities, using questionnaire surveys and on-site damage distribution surveys, for data to supplement our instrumental measurements of strong ground motions. As an alternative to earthquake intensity investigations, our attention has focused on the usage of videotaped pictures that have recorded objects shaken by strong ground motions during earthquakes. Motivation for this study is derived from the experiences of recent damaging earthquakes in Japan, where TV stations broadcast such videos quite soon after the events. We were also stimulated to present this study by the fact that in Japan video cameras have become extremely widespread throughout the country. The number of video cameras in Japan exceeds 10 million, whereas the number of strong-motion seismometers installed in Japan as of February 1997 is about 6,000, according to a recent survey conducted by the Japan Science and Technology Agency. Also, in Japan we have over 50,000 convenience stores. In most of these stores, several security cameras are installed and are always in operation. Moreover, an enormous number of security cameras are installed at automatic teller machines (ATM's). Recently, videotaped pictures from convenience stores have attracted the attention of some earthquake engineers and seismologists in works by Ohori et al. (1995a, 1995b) and Kikuchi (1995a, 1995b). Ohori et al. (1995a) utilized the videotaped pictures from security cameras in convenience stores in Kushiro to calibrate the seismic intensities obtained from their questionnaire …