ABSTRACT

In this article, the authors make a brief report on the strong ground motions observed in the midst of the heavily damaged zone during the 16 April Mw 7.0 mainshock of the 2016 Kumamoto, Japan, earthquake. The observation was accidentally made by a dense seismic array that was deployed by the authors with the intention of observing aftershocks of the 14 April Mw 6.2 event, which later turned into the foreshock of the Mw 7.0 event. The observed ground motions are characterized by a large‐amplitude pulse with an approximate period of 1 s that is predominant in the east–west (EW) components, which is comparable in shape to those observed during the 1994 Northridge and the 1995 Kobe earthquakes. In particular, the observed ground motions exceed the largest observed ground motions during the 1995 Kobe earthquake in terms of spectral accelerations in the 0.5–1.2 s period range. The importance of these records is that this was observed in the midst of a heavily damaged zone, where the ratio of totally collapsed wooden houses, due either to the foreshock or the mainshock, reportedly reached as high as 50% causing significant loss of life. Therefore, the records should be used in future research to reveal how the buildings were damaged, to develop appropriate measures, and to mitigate damages attributed to future large earthquakes.

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