HIGH-RESOLUTION SEISMIC REFLECTION SURVEY AT A PROPOSED DAM SITE
A high-resolution seismic reflection survey was conducted at a proposed dam site located in an incised valley of Tara Volcano, western Kyushu, Japan. The purpose of the survey was to delineate the shallow reflectors within volcaniclastic flow deposits and to assess whether they were deformed by recent faulting. Geological assessment of a dam site is quite important for the dam safety. From the viewpoint of geology, geological setting and its structure is the key to judge the site safety for a dam. At the proposed site, the surface is covered by volcaniclastic flow sediments, which overlie Paleogene sandstone formation with irregular unconformity. The shape of this unconformity was the issue to be made clear. Additional problem was whether the volcaniclastic flows were massive or stratified. Foundation rocks are required to have the enough strength to bear the load of dam body. The volcaniclastic rocks at the site were tested to have moderate strength, but the rocks were partly brecciated and permeable revealed from a grid drilling program. Regretfully, even the widely spaced drilling had provided insufficient information on spatial extent of such problematic zones. From the point of view of seismicity, the site and its surrounding area should be tectonically quite. However, several geomorphic lineaments were identified near the site. It was required to evaluate whether the lineaments are volcanotectonic origin or seismogenic. We set three seismic lines on river terraces along the stream and covered about 1.1 km long section including the proposed dam site. The survey result clearly reconstructed the layered structure in the volcaniclastic deposits, and imaged the unconformity with underlying sandstones. The shallow geologic structure beneath the dam site gently dips southward in concordant with the volcaniclastic flow direction, and neither mappable faulting nor deformed structure was imaged in the section, which means the site was tectonically stable during the recent geologic period.
Large dam Dam site geology Concealed fault Seismic reflection High-Resolution
Inazaki Tomio Sakamoto Tadahiko
Public Works Research InstituteMinami-hara 1-6, Tsukuba, JAPAN Public Works Research Institute Minami-hara 1-6, Tsukuba, JAPAN
国际会议
西安
英文
1-9
2005-11-01（万方平台首次上网日期，不代表论文的发表时间）