Journal of Natural Disaster Science

RESTORING CLIPPED RECORDS OF NEAR-FIELD STRONG GROUND MOTION DURING THE 1995 HYOGO-KEN NANBU (KOBE), JAPAN EARTHQUAKE

Takao KAGAWA
Researcher, Geo-Research Institute, Osaka Soil Test Laboratory, Osaka
Kojiro IRIKURA
Professor, Disaster Prevention Research Institute, Kyoto University, Kyoto
and
Isamu YOKOI
President, Tokyo Sokushin Co. Ltd., Tokyo

(Received 12 September, 1996 and in revised form 11 December, 1996)

Abstract

During the 1995 Hyogo-ken Nanbu (Kobe), Japan Earthquake, the Committee of Earthquake Observation and Research in the Kansai Area (CEORKA) obtained strong ground motion records near the heavily damaged area. Records at the Kobe University, Kobe (Motoyama) and Amagasaki sites unfortunately were clipped because of large ground motion or seismometer imbalance. The first two sites are very close (less than 2 km) to the source fault, and the Amagasaki site is about 10 km from the east edge of the fault. The clipped data are considered very important to the study of the source process and strong motion characteristics.

These ground motions were recorded by servo velocity type seismographs. The clipping characteristics of this type of seismograph were studied. Under clipping, the seismograph shifted the zero line of the record proportional to the clipped amplitude. The clipped records were corrected to restore the actual ground motion at the sites by numerically solving the equations that control the instruments.

After correction of the clipped portions of the records, the maximum velocity of the vertical component at the Kobe University site was found to be about 19 cm/s. At the Kobe (Motoyama) site, the respective maximum horizontal and vertical velocities were about 78 and 50 cm/s. The restored horizontal peak velocity at the Amagasaki site was about 50 cm/s.

Key words

1995 Hyogo-ken Nanbu Earthquake, strong motion record, clipped record, servo velocity seismograph