[HQR06-P03] Characteristics of gradient of valley plaine in Ibaraki Prefecture
Keywords:valley plaine, garadient, liquefaction
As a result, the valley plain/flood plain steeper than gradient 1/100 accounted for only less than 10 percent by the extended, and its location was limited to a valley head. The gradient of the valley plain dissecting the plateau is steeper than roughly 1/500. Liquefaction caused by the 2011 off the Pacific coast of Tohoku Earthquake didn't occur at the valley plain steeper than gradient 1/500.
On the other hand, most of the flood plain along great rivers in Ibaraki Prefecture have a gentler gradient than the gradient of approximately 1/500, and no particular correlation was found between the liquefaction occurrence spots and the gradient.
For the liquefaction risk assessment based on the landform classification, the valley plain/flood plain needs to be divided into the flood plain along the great rivers and the valley plain dissecting the plateau, and the valley plain has a gradient more than 1/500.
In addition, as a result of sampling using a hand auger and particle size analysis in the valley bottom plain dissecting the plateau, coarse sand was dominant at a deeper than 3 m in the upstream core with a gradient more than 1/100. The result of analysis is supporting the supposition that a rough grain-size deposits are accumulated at steeper valley plains.
Prof. Naofumi Yamaguchi of Ibaraki University lent us bowling machinery. Miss. Kaho Hashimoto who is Ibaraki University student and her family had been very kind for an offer in land of sampling sites.