PEMETAAN TINGKAT RESIKO GEMPABUMI DAERAH LIWA DAN SEKITARNYA BERDASARKAN PENGUKURAN MIKROTREMOR THE RISK LEVEL MAPPING OF EARTHQUAKE IN LIWA AND VINICITY BASED ON MICROTREMOR MEASURMENT

Lidia Hartati, Prof. Dr. Sismanto

2014 | Tesis | S2 Ilmu Fisika

Pengukuran mikrotremor telah dilakukan di daerah Liwa dan sekitarnya, Lampung Barat, Lampung. Pengukuran ini dilakukan untuk mengetahui sebaran tingkat resiko gempabumi berdasarkan nilai Peak Ground Acceleration (PGA) yang didukung oleh nilai periode dominan , amplifikasi , indeks kerentanan seismik , ketebalan lapisan sedimen , dan ground shear strain . Pengukuran dilakukan bersama Pusat Survei Geologi (PSG) Bandung, dengan menggunakan seismometer tiga komponen tipe Lennartz 0,2 Hz SARA sebanyak 66 titik pengukuran. Data dianalisa dengan menggunakan metode Horizontal to Vertical Spectral Ratio (HVSR). Hasil analisa HVSR menghasilkan frekuensi dominan dan amplifikasi . Kemudian menghitung nilai indeks kerentanan seismik, ketebalan lapisan sedimen, PGA dan ground shear strain. Perhitungan nilai PGA dilakukan dengan menggunakan persamaan empiris Kanai untuk gempabumi tanggal 15 Februari 1994. Selanjutnya dilakukan perhitungan tingkat resiko gempabumi. Hasil penelitian menunjukkan bahwa daerah Liwa dan sekitarnya memiliki nilai PGA berkisar antara 123,5–483,5 gal dengan intensitas VIII–X Modified Mercalli Intensity (MMI). Nilai periode dominan berkisar antara 0,1–1,6 detik. Nilai amplifikasi berkisar antara 2,4–5,6. Nilai ketebalan lapisan sedimen berkisar antara 11,1–203,1 meter. Nilai indeks kerentanan seismik berkisar antara 0,9–58,5 detik. Nilai ground shear strain berkisar antara 0,004–0,133 gal detik. Berdasarkan klasifikasi tingkat resiko gempabumi dari data tersebut dapat disimpulkan bahwa daerah Liwa dan sekitarnya sangat rentan terhadap gempabumi, yang memiliki tingkat resiko dari resiko besar satu sampai resiko sangat besar satu dengan intensitas skala terbukti VIII–IX MMI dan IX–X MMI. Kata Kunci: Mikrotremor, HVSR, Peak Ground Acceleration, Ketebalan Lapisan Sedimen, Indeks Kerentanan Seismik, Ground Shear Strain.

Microtremor measurments have been conducted in Liwa and vinicity, Lampung Barat, Lampung. This measurment is performed to determine the risk level distribution of earthquake based on Peak Ground Acceleration (PGA) , which is supported by dominan period To values, amplification , ground seismic vulnerability index , sediment layer thickness and ground shear strain .The measurements were performed by Geological Survey Center (PSG) Bandung, by using three componens seismometer Lennartz type 0.2 Hz SARA at 66 points. The data analysis using Horizontal to Vertical Spectral Ratio (HVSR) method. The results of the HVSR analysis are the dominan frequency and amplification . Then the calculation of the ground seismic vulnerability index, sediment layer thickness, PGA and ground shear strain. The calculate of PGA values using by Kanai empirical equations for earthquake February 12, 1994 event. Then the calculation performed of the risk level of earthquake. The results show that the Liwa and vinicity have PGA values rangs from 123.5–483.5 gal or VII-IX Modified Mercalli Intensity (MMI). Dominan period values rangs from 0.1–1.6 second, amplification values rangs from 2.4–5.6, thickness sediment layer values rangs from 11.1–203.1 meters, the ground seismic vulnerability index values rangs from 0.9–58.5 second and ground shear strain values rangs from 0.004–0.133 gal second. Based on the risk level classification of earthquake from these data, can be concluded that the Liwa and vinicity vulnerable of the earthquake, which has the risk level is from the big risk one to the bigger risk one, with proven scala VII-IX MMI and IX-X MMI. Key words: Microtremor, HVSR, PGA, Sediment Layer Thickness, Ground Seismic Vulnerability Index, Ground Shear Strain.

Kata Kunci : Mikrotremor, HVSR, Peak Ground Acceleration, Ketebalan Lapisan Sedimen, Indeks Kerentanan Seismik, Ground Shear Strain.