Abstract—Microtremors measurement in Kebon Agung area (deltaic area of Porong river) which is located in the district of Sidoarjo, Indonesia using short period seismometer type TDL-303S (three components) was conducted at 23 sites with sampling rate of 100 Hz. Geologically, this location is a deltaic sedimentation which will be used as a new artery way of Porong. This area will replace the Porong toll road which is broken, caused by Mud Volcano in Sidoarjo. Measurements spacing used in this research was 400 m with average recording time was 30 minutes.
Microtremors analysis is performed using Horizontal to Vertical Spectral Ratio (HVSR) to understand dynamic characteristic of sediment layer, such as natural frequency (f0) and peak ratio of HVSR (A). This analysis is very useful for mapping of seismic microzonation, amplification factor, and vulnerability of seismic index.
The results showed that the range of natural frequency in Kebon Agung area is between 0,573 and 1,264 Hz with average is below of 1 Hz. Spectral ratio of H/V ranges from 6,265 to 12,356. By using natural frequency and peak of HVSR summation, it is concluded that Kebon Agung area has moderate potential of seismic risk. The values of seismic index vulnerability range from 43 to 150. From these three analysis, it is estimated that a site in the northern part of the river has the highest vulnerability of seismic risk.

Index Terms—HVSR, natural frequency, vulnerability of seismic index, microtremors, seismic microzonation.

Susilo is with the Geophysics Study Program, Physics Department, Faculty of Science, and Geoscience and Hazard Mitigation Research Center, University of Brawijaya Malang (65145), Indonesia (e-mail: adisusilo@ub.ac.id).
S. H. Wiyono is with the Meteorological, Climatology and Geophysics Agency, Tretes, Pandaan, Indonesia (e-mail: shwiyono@yahoo.de).

 

Cite: Adi Susilo and Samsul H. Wiyono, "Frequency Analysis and Seismic Vulnerability Index by Using Nakamura Methods at a New Artery Way in Porong, Sidoarjo, Indonesia," International Journal of Applied Physics and Mathematics vol. 2, no. 4, pp. 227-230, 2012.