ANALISIS PENGARUH KARAKTERISTIK SEDIMEN TERHARAP INDEKS KERENTANAN SEISMIK KOTA MAKASSAR

ANDI AZHAR RUSDIN, Dr. Danang Sri Hadmoko, M.Sc.

2015 | Tesis | S2 Geografi

Kota Makassar merupakan salah satu kota yang rentan akibat gempabumi karena terletak di atas endapan aluvium. Penelitian ini dilakukan menggunakan 100 titik pengukuran mikrotremor. Tujuan dari penelitian ini adalah: (1) untuk mengetahui sebaran ketebalan sedimen di Kota Makassar, dan (2) untuk mengetahui pengaruh karakteristik sedimen terhadap indeks kerentanan seismik. Penelitian ini menggunakan teknik Standard Spectral Ratio (SSR) dan teknik Horizontal to Vertical Spectral Ratio (HVSR). Analisis ini digunakan untuk mengetahui sebaran frekuensi dominan serta sebaran ketebalan sedimen, Selain itu analisis statistik juga digunakan untuk mengetahui hubungan antara karakteristik sedimen dan kedalaman muka airtanah dengan variasi indeks kerentanan seismik. Hasil penelitian menunjukkan bahwa sebaran frekuensi dominan memiliki hubungan signifikan dengan ketebalan sedimen. Frekuensi dominan rendah memiliki ketebalan sedimen tebal dan terdapat di bagian barat Kota Makassar. Ketebalan sedimen di bagian timur Kota Makassar lebih tipis karena memiliki nilai frekuensi dominan yang tinggi. Teknik pengukuran Standard Spectral Ratio (SSR) sangat tepat digunakan untuk mendapatkan nilai ketebalan sedimen dibandingan menggunakan Teknik Horizontal to Vertical Spectral Ratio (HVSR) karena hasil ketebalan sedimen SSR mendekati nilai ketebalan sedimen hasil pengeboran. Terdapat hubungan antara karakteristik sedimen dan kedalaman muka airtanah terhadap variasi indeks kerentanan seismik. Indeks kerentanan seismik tinggi terdapat di lapisan sedimen pasir yang tebal dengan ketebalan sedimen yang tebal serta kedalaman muka airtanah yang dangkal, sebaliknya indeks kerentanan rendah terdapat pada lapisan sedimen pasir yang tipis dengan batuan tufa dangkal dan memiliki ketebalan sedimen yang dangkal serta kedalaman muka airtanah dalam. Kata kunci: karakteristik sedimen, indeks kerentanan seismik, SSR, HVSR.

Makassar is the one of cities that is vulnerable due to earthquakes because it is located above the aluvium sediments. This study was conducted using 100 microtemor measurement points. The aim of this study are: (1) to determine sediment thickness distribution in Makassar, and (2) to determine the effect of sediment characteristic of the seismic vulnerability index. This study used the Standard Spectral Ratio technique (SSR) and the Horizontal to Vertical Spectral Ratio techniques (HVSR). This analysis is used to determine the distribution of the dominant frequency and distribution of sediment thickness. Furthermore, statistical analysis was also used to determine the relationship between the characteristics of the sediments and the depth of the groundwater level over variation of seismic vulnerability index. The results showed that the dominant frequency distribution has a significant relationship with the thickness of the sediments. The low dominant frequency has thicker sediment thickness and contained in the western area of the city of Makassar. In reverse, the thickness of the sediments in the eastern area is thinner because it has a high value of the dominant frequency. Measurement techniques of Standard Spectral Ratio (SSR) is ideal to use to get the value of the thickness of sediment compared using techniques Horizontal to Vertical Spectral Ratio (HVSR) as the result of SSR sediment thickness approaches the sediment thickness drilling results. There is a relationship between the characteristics of the sediments and the depth of groundwater level on the variation of the seismic vulnerability index. High seismic vulnerability index contained in a thick layer of sand sediments with thick sediment thickness and shallow depth of groundwater table, otherwise low vulnerability index contained in a thin layer of sand sediments with shallow tufa rock and shallow sediment thickness and depth of the groundwater table. Keywords: characteristics of sediment, seismic vulnerability index, SSR, HVSR

Kata Kunci : karakteristik sedimen, indeks kerentanan seismik, SSR, HVSR; characteristics of sediment, seismic vulnerability index