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Microtremor Survey and Spectral Analysis of a Coseismic Landslide: a Case Study in Subao Village,
Ningxia, China〇Xiaobo LI, Jingshan BO, Issei DOI, Gonghui WANG, Toshitaka KAMAI

Seismic landslide is a common geological disaster,

To study the spectrum characteristics of Subao

some of which has the characteristics of “large scale,landslide site, we used a digital accelerograph tolongsurface,measure the microtremor on the sliding mass,fragmented slip mass, heavy losses and high risk”,

landslide bed and soil mass of slopes around theusually causing serious casualties and economic losses.

landslide (Fig. 2). The sampling rate is 200, and theThe study of the spectrum features of typical landslide

data acquisition time is about 600s.

sliding

distance,

gentleslidingsites is crucial to better understanding the possible site
response during earthquake, and then evaluate the riskof landslide. Therefore, we chose the Subao landslide
to carry out microtremor survey and spectral analysis.
Subao landslide (Fig. 1) located in Subao village, Xijicounty, Ningxia Hui antonomous region, China, which
was a giant coseismic loess landslide induced by 1920
Haiyuan great earthquake (M = 8.5). The landslide
was located in the IX-grade seismic intensity area, ofshear liquefaction failure mode and belonged to aloess contact surface landslide. The landslide plane
was of irregular configuration, about 1435 m in length,
400 m in width and 30 m in mean thickness, of theoriginal height of 153 m, gradient of 12°and apparent
friction factor of 0.14, a typical low angle and longFig. 2 The layout of microtremor points

distance landslide.
Then, based on the H/V method, applying the open
sourcesoftwareGeopsy(www.geopsy.com)

tocalculate and analyze the test data. The results areshown in Fig. 3. According to the results, we can draw
the following conclusions: (1) Most H/V curves of soil
mass of slopes around the landslide had clear peak,
the range of the predominant frequency is 2.2~2.9Hz,
Fig. 1 The full view of Subao landslide

the peak amplification factor is 2.3~4.0, which were(Lens pointing, 165°)

well reflected the magnification effect of groundmotion about the soil mass and terrain; (2) H/V curves
1Fig. 3 The H/V curves for different points. The points M01~M11 are on the slopes around the landslide ,the points
M12~M13 are on the sliding mass, and the points M14~M15 are on the landslide bed.

of the sliding mass were relatively gentle, multi-peakunable to well reflect the spectral features of thetype, without significant predominant ranges, the peaklandslide site.

amplification factor is 1.9~2.2, reflecting the complex

Accordingly, we found the spectral characteristics

interface of the soil after sliding and the no obvious

of soil mass of the slopes around the landslide are theamplification effect of the ground motion; (3) H/Vreliable parameters for studying the dynamic stability

curves at the outcrop of the landslide bed were had aof the landslide site. This would not only provide anarrow and steep predominant frequency band, thecriterion

range of the predominant frequency is 2.4~2.6Hz, thegeomechanical models of slopes, but also provide thepeak amplification factor

important calculation parameter for the inversion ofis 4.6~4.8,

showingsignificant topographic effect; (4) Compared with theforthereasonableestablishment

ground motion based on coseismic landslide.

stable soil mass of slopes around the landslide, thesliding mass was of complicated soil structure and thespectral characteristics were not obvious, therefore
2of