A microtremor analysis for microzonation of seismic vulnerability index by using horiziontal to vertical spectral ratio in the southern area of Klaten regency

Abstract

The dominant frequency and amplification factor are the parameter used to determine the value of seismic vulnerability index of an area. This research aims to determine the f0 and A0 in the southern area of Klaten regency. Besides, in this research a value range of Kg in the southern area of Klaten regency is obtained.This research was done in the southern area of Klaten regency by using P.A.S.I Seismograph Mod. 16S24-P, 3D Borehole Geophone Model GFA 60/100. The data acquisition was done in 12 different locations with the interval being about 5 km. In each location, the measurement needed 20 minutes and was done with three times repetition. The microtremor data obtained were processed by using the Geopsy software so that HVSR curve was obtained. From the HVSR curve, the f0 and A0 value can be determined which then were used to determine the value of Kg. After that, the value range of f0, Ao, and Kg obtained was made into a contour map by using Software Surfer.The result of the research shows that the value of f0 in the southern areas of Klaten regency is in the range of 4.104 Hz to 9.300 Hz, the value of A0 is in the range of 1.326 to 2.328, and the value of Kg is in the range of 4.259 × 10-5 s2/cm to 59.873 × 10-5 s2/cm. The microzonation result with the minimum Kg value of 3.00 × 10-1 s2/cm is located in Pedan Subdistrict and the maximum Kg value of 15.704 × 10-1 s2/cm is spread in Prambanan Subdistrict.