Sequential processes in a landslide hazard at a slate quarry in Okayama,Japan |
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Authors: | Hiroshi Suwa T Mizuno S Suzuki Y Yamamoto K Ito |
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Institution: | (1) Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji Kyoto, 611-0011, Japan;(2) Seismic Product Line, Schlumberger K.K., Sagamihara 229-0006, Japan;(3) Department of Earth Sciences, Okayama University, Okayama 700-8530, Japan;(4) Japan Engineering Consultants Co., Ltd., Osaka 531-0072, Japan |
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Abstract: | The 12 March 2001 landslide at a slate quarry in Okayama, Japan killed three workers. Composite studies based on field surveys
of the landslide slope, interviews with local residents and quarry workers, and inspections of hydrological and seismological
data have been used to clarify the causes of this slide and its movements. The results indicate that the landslide was enabled
firstly by the steepness of the slope, which had been undercut by river; secondly, the structure was that of a dip-slope that
was prone to deep-seated slides along bedding planes; thirdly, numerous joints and faults were present. Surprisingly, rainfall,
earthquakes, and explosions do not appear to have played any role in the triggering of this slide. The interviews demonstrated
that the frequency of precursory failures increased over a period of several hours before the 12 March 2001 landslide. Inspection
of the seismograph records and the eyewitness evidence both indicate that the main part of the landslide consisted of two
phases of slope failure within 23 s. After the slide, the frequency of the failures gradually decreased with time over a period
of several days. Three new terms are proposed for landslides: foreslide, mainslide, and afterslide, following the terms foreshock,
main shock, and aftershock used in seismology. |
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Keywords: | Quarry Landslide Dip-slope Undercut slope Precursor Progressive failure |
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