Microzonation of the seismically active region along the Seulimum fault

Abstract

Banda Aceh and Aceh Besar regency is located between the two active faults, the Seulimeum and Aceh segments. In the near future, a large infrastructure development will be constructed in an area closed to the Seulimum fault. One of the development areas is the Campus II of Universitas Syiah Kuala. To prevent possible damage of infrastructure by a devastating earthquake, the developer needs to consider soil and rock types where the building is located. A region characterized by soft soil can lead to seismic amplification which can cause the damage of buildings and infrastructure. The objective of the research is to investigate the types of soil and rocks, called microzonation, in a seismically active region closed to the Seulimum fault. The types of rocks or soils can be classified based on the values of shear wave velocity (Vs) derived from the microtremor data. The acquisition of seismic data was carried out using a 4.5 Hz triangle array geophone at 35 measurement points. The microtremor data at each location was analysed by using the Spatial Autocorrelation (SPAC) to obtain the Rayleigh wave dispersion curve. The Vs values are then classified based on SNI 1726:2019. The results of the microtremor analysis showed that the Vs values are relatively high ranging from 300 m/s – 1500 m/s at different depths associated with hard rock as also observed in the field. At depth of 30 km, Vs30 is higher in the west and in the southeast while in the north the velocity is lower at around 300 m/s. It is suggested to investigate more detail and local type of rocks before infrastructure development to mitigate possible damages.