Because earthquake shock sometimes decreases the frequency at which the ground vibrates, especially at soft soil sites, the strength of strong ground motion during an earthquake is an important characteristic that can affect the degree to which geological structures and buildings collapse.
Most research focuses on the reduction in peak frequency of site response caused by strong ground motion. But in an article published recently in the journal Geophysical Research Letters, Kaoru Sawazaki and colleagues at Japan's Tohoku University sought instead to document peak frequency recovery following large earthquakes.
By analyzing coda waves, which are seismic wave trains generated by energy scattering due to soil and crustal heterogeneities, the authors estimated peak frequency recovery using data from seismometers vertically separated in boreholes at two sites following Japan's 2000 Western Tottori Earthquake, and at a site following the 2003 Tokachi-Oki Earthquake.
The researchers found that the peak frequency at relatively solid sites after the Western Tottori Earthquake took a few years to recover to the value before the earthquake, but that the weak site after the Tokachi-Oki earthquake recovered within an hour.
Authors: Kaoru Sawazaki, Haruo Sat, Hisashi Nakahara, and Takeshi Nishimura: Department of Geophysics, Graduate School of Sciences, Tohoku University, Sendai, Japan.
Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL027938, 2006
The above story is based on materials provided by American Geophysical Union. Note: Materials may be edited for content and length.
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