Microtremor Assessment to Investigate the Local Site Response and the Depth of Weathering Rock at Institut Teknologi Sumatera Campus Area

Maria Rosalita Pujiastuti Sudibyo, Erlangga I. Fattah, Cahil Suhendi, Reza Rizki

Abstract


Local site effects related to the local geology can influence the damage of earthquake, by amplifying or deamplifying the horizontal movement of ground motion. To characterize the site effects in a local area, the natural frequency and the amplification factors can be estimated by performing Horizontal-to-Spectral Ratio on microtremor data. The amplification factors and natural frequency obtained then can be used to estimate the seismic vulnerability and the depth of the bedrock. This method is applied by recording the microtremor data in 1.5x1.5 km2 ITERA campus area, deploying 11 points of measurements. The recording of 45 to 60 minutes long for each point has been done to accommodate the lowest possible natural frequency we may obtain. The HVSR estimation shows that there are two predominant frequency, F0 and F1, ranging from 0.7 to 1.31 Hz and 3.88 to 8,71 Hz. These two dominant frequencies are associated with two layers of tuff, a soft weathered laying on a thicker and stiffer tuff rock layer. The amplification factors Ao are varied from 2.5 to 9 and is considered as the low bound of the real amplification factor. The depth of the soft weathered tuff is estimated ranging from 8 to 18 m. The seismic vulnerability estimated from this research is ranged from 7 to 65, implying that the area has mid-level of vulnerability.


Keywords


site effect; microtremor; HVSR; ground motion

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References


SESAME European Research Project (2004), Guidelines for the Implementation of the H/V Spectral Ratio Technique on Ambient Vibrations: Measuring, Processing, and Interpretation, European Commision – Research General Directorate Project.

Panou, A., Hatzidimitriou,K, and C. Papazachos (2005), Ambient noise horizontal-to-vertical spectral ratio in site effects estimation and correlation with seismic damage distribution in urban environment: the case of the city Thessaloniki (Northern Greece). Soil Dynamics and Earthquake Engineering, 25, 261-274.

Nakamura, Y. (1989), A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface, Report of Railway Technical Research Institute (RTRI), Vol 30, No. 1.

Nakamura, Y. (2000), Clear identification of fundamental idea of Nakamura's technique and its applications, Proceedings of the XII World Conference Earthquake Engineering. Paper no 2656

Mangga, A., Amirudiddin, S. Suwarti, T., Gafoer, S., and Sidarto (1994). Geology of Tanjungkarang Quadrangle, Sumatera. Geological Research and Development Centre, Bandung, 19pp.

Konno, K., and T. Ohmachi (1998), Ground motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremors, Bull. Seism. Soc. Am, 228-241.

Lermo, J., and F. Chavez-Garcia (1994), Are microtremors useful in site response evaluation? Bull. Seism. Soc. Am, 84, 1350-1364.

Bonilla, L., Steidl, J., Tumarkin, A., and R. Archuleta (1997), Site Amplification in the San Fernando Valley, California: Variability of Site-Effect Estimation using the S-Wave, COda, and H/V Methods, Bull. Seism. Soc. Am, 3, 710-730.

Wald, D.J., and T.I. Allen (2007), Topographic Slope as a Proxy for Seismic opographic Slope as a Proxy for Seismic Site-Conditions (V 30S ) Around the Globe Around the Globe, U.S. Geology Survey, Virginia.

Allen, T.I., and D.J. Wald (2009), On the Use of High-Resolution Topographic Data as a Proxy for Seismic Site Conditions (VS30), Bull. Seism. Soc. Am,99, 935-943.


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