Hakim, Aliful Choirul (2019) Penentuan Ground Profile dan Peak Surface Acceleration (PSA) dengan Metode Inversi Mikrotremor Single Station untuk Zonasi Bahaya Gempabumi Pulau Lombok. Other thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Terdapat dua fenomena gempabumi yang cukup merusak di tahun 2018 sebesar M 6,4 dan M 7 di Kabupaten Lombok Timur. Namun kerusakan parah terjadi di wilayah Kabupaten Lombok Barat, Kota Mataram, dan Kabupaten Lombok Utara dimana ketiga lokasi tersebut jauh dari episenter gempa. Hal ini membuktikan bahwa potensi kerusakan infrastruktur tidak hanya bergantung pada magnitudo dan fungsi jarak sumber gempa, melainkan adanya local site effect atau karakteristik tanah. Penelitian ini bertujuan untuk mengetahui karakteristik dinamis tanah berdasarkan parameter Periode Dominan (Tdom), Vs30, dan site classification serta mendapatkan persebaran nilai Peak Surface Acceleration (PSA). Metode yang digunakan yaitu analisis HVSR (Horizontal to Vertical Spectral Ratio) dan inversi kurva eliptisitas gelombang Rayleigh dari pengukuran mikrotremor single station. Hasil pengolahan yang didapat menunjukkan bahwa Kabupaten Lombok Barat, Kota Mataram, dan bagian barat Kabupaten Lombok Utara didominasi lapisan sedimen yang lunak dibuktikan dengan nilai Tdom relatif tinggi (0,60 detik - 2,16 detik) dan Vs30 relatif rendah (185,18 m/s – 460.54 m/s) serta sebagian besar masuk pada kategori kelas situs SD (stiff soil / tanah lunak). Model ground profile kecepatan gelombang geser (Vs) 3D memperlihatkan adanya penebalan sedimen di ketiga wilayah yang sama hingga ±100 meter. Sehingga wilayah ini rentan akibat deformasi tanah akibat gempa. Adapun distribusi nilai Peak Surface Acceleration (PSA) didapat berdasarkan pengaruh site class terhadap Peak Ground Acceleration (PGA) berdasarkan SNI 1726:2012. Pulau Lombok bagian selatan memiliki nilai PSA relatif tinggi untuk semua jenis periode, sedangkan Pulau Lombok bagian barat didominasi nilai PSA periode panjang 1,0 detik (SM1). Tingginya nilai PSA berpotensi menimbulkan guncangan tanah yang cukup kuat saat terjadi gempa. Penelitian ini diharapkan dapat menjadi referensi dalam pembuatan desain respon spektra untuk meminimalisir kerusakan infrastruktur gedung berbagai tingkat akibat kejadian gempa.
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There are two fairly destructive earthquake phenomena in 2018 of M 6.4 and M 7 in East Lombok District. However, severe damage occurred in the West Lombok District, Mataram City, and North Lombok District where the three locations were far from the earthquake epicenter. This proves that the potential for infrastructure damage does not only depend on the magnitude and the earthquake source distance, but rather the presence of local site effects or soil characteristics. This study aims to determine the dynamic characteristics of the soil based on the parameters of Dominant Period (Tdom), Vs30, and site classification and get the distribution of Peak Surface Acceleration (PSA) values. The method used are HVSR analysis (Horizontal to Vertical Spectral Ratio) and inversion of Rayleigh wave ellipticity curve from single station microtremor measurements. The results of processing obtained showed that West Lombok Regency, Mataram City, and the western part of North Lombok Regency were dominated by sedimentary layers which were softly proven by relatively high Tdom values (0.60 seconds - 2.16 seconds) and relatively low Vs30 (185.18 m / s - 460.54 m / s) and included in the SD (stiff soil / soft soil) site category. The shear wave velocity (Vs) 3D ground model shows sediment thickening in the same three regions up to ± 100 meters. So that this region is vulnerable due to soil deformation due to the earthquake. The distribution of Peak Surface Acceleration (PSA) values is based on the effect of site class on Peak Ground Acceleration (PGA) based on SNI 1726: 2012. The southern part of Lombok Island has a relatively high PSA value for all types of periods, while the western part of Lombok Island is dominated by a long period of 1.0 seconds PSA (SM1). The high value of PSA has the potential to cause ground shaking hazard that are strong enough when an earthquake occurs. This research is expected to be a reference for the design of spectra response to minimize damage of building infrastructure at various levels due to earthquake events.
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