地盤研究財団
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Explore the geology
 

Research on the geological environment of the area

Depending on the area, the formation and deposition conditions in the ground are different. There are also many active faults. Such geological information is extremely important basic data in construction work and earthquake disaster prevention examination. The Foundation conducts research on the geological environment of the region, including analysis of sedimentary environment and age of strata, underground structure and active fault investigations.
Geological analysis
By clarifying the sediment age and sedimentary environment (marine / non-marine etc.) and comparing it with multiple survey data in the vicinity, it is possible to know in detail the distribution or geological structure of the stratum in that area.
▲Comprehensive comparison of various analysis results
■Main geological analysis
Analysis item Information obtained
Microfossil comprehensive analysis Sedimentary environment (marine / non-marine, etc.)
Diatom fossil analysis Sedimentary environment (marine / non-marine, etc.)
14C dating Absolute age (about 50,000 years ago-present)
Volcanic ash analysis Estimate of age, wide area contrast of strata
Magnetic susceptibility continuous measurement Detection of volcanic ash that can not be observed with the naked eye

Active fault investigation

Especially since the 1995 Hyogoken Nanbu Earthquake, the importance of seismic examination for inland earthquakes has increased. At the Foundation, we are working on the underlying fault investigation.

●Understanding the exact location and nature of faults
Find the place where the bedrock or stratum etc. has been locally altered (crushed) by fault activity, and estimate the scale of activity from fault continuity, direction, displacement (up and down, horizontal displacement) etc.

●Understanding of active fault activity history and latest activity time
We will conduct surveys to determine what kind of recurrent interval the fault will be in and what time it will happen next.

  地表地質踏査
▲Reflection seismic profiling of the southern part of the Uemachi fault zone
(Osaka Prefecture 1997)
▲Summary of the underground geological structure of the Uemachi fault zone
(Osaka Prefecture 1998)
Seismic reflection survey
Active fault (by urban area active fault map)
Active faults added by the Osaka Prefecture Regional Active Fault Investigation Committee
Estimated active fault (underground) (by urban area active fault map)
Estimated active fault (above ground) (by urban area active fault map)
Foundation depth (m) confirmed in reflection cross section
Foundation depth (km) (Inoue et al. 1997)

Investigation of the Uemachi fault zone
"Research on the Uemachi fault zone" Osaka Prefecture 1996-1998, Osaka City 1995


The Uemachi fault zone, which traverses the Osaka Plain, has been studied and reported since the 1960s. In this survey, we conducted seismic reflection surveys, boring, trench surveys, etc. and compiled them together with the existing survey and research materials. As a result, there are several occurrences of basement rock and sediment formation and deformation of the strata along the Uemachi fault zone, the fault line branches into several from north to south, and the vertical displacement also differs depending on the survey area It was understood in detail.

Strata appeared by cut-and-cut construction of building construction

The photo shows an example of observing the wall surface that accompanies the excavation work when a high-rise building was constructed in the Osaka city area. It is a very valuable opportunity to be able to continuously observe the strata in urbanized areas like Osaka. In this survey, we were able to record the state of the formation to a depth of 30 m.

A state of seismic intensity around 8 m.
In the alluvial sand layer, weeding (fine striated sedimentary structure) is observed.

 



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