Measurement of ground response of Semarang coastal region risk of earthquakes by Horizontal to Vertical Spectral Ratio (HVSR) microtremor method

Abstract

The study was conducted to determine the response of the Semarang Coastal area to eartquakes by measuring the micro tremor response with 3 component seismographs at 110 locations on the Semarang coastal region that were distributed almost evenly. From the micro tremor data, it is processed using Gyopsy software to get the dominant frequency and amplification values. The dominant frequency value and its amplification are then made a map with surfer 13, and the results are then overlaid on the RBI map for qualitative interpretation. The results of this study are dominant frequency and their amplification in the Semarang coastal region maps. The dominant frequency values range from 0.5 Hz - 10 Hz. Based on the dominant frequency values, can be grouped into three categories, namely low frequency values that are less than 2.5 Hz associated with sediment thickness values of more than 30 m and areas with moderate frequencies with values between 2.5 - 4 Hz associated with sediment thickness 10 - 30 m, and high frequency indigo between 4 Hz - 10 Hz is associated with a sediment thickness of 5-10 m. Areas with low frequencies dominate the study area. Areas with medium and high frequency values are only a small part of the study area. The amplification values vary between 0.5 - 8.5. While the amplification value can also be grouped into 3 parts, namely the amplification of less than 2.75 associated with hard rocks almost dominates the central part of the study area, the amplification value between 2.75 - 5.15 associated rocks or soil with moderate violence is only a small part as between low and high values in the study area, and values of more than 5.15 associated with soft soils that dominate the northern and the southern part of the study area.. If the area around Semarang has an earthquake, the location with a large amplification will be more prone to earthquake disasters.