ABSTRAK Gempabumi dapat menimbulkan bahaya likuifaksi yang dapat merusakkan bangunan dan sarana infrastruktur khususnya di wilayah perkotaan di Indonesia. Investigasi geoteknik bawah permukaan telah dilakukan di daerah Patalan, Bantul, Yogyakarta, untuk mendapatkan gambaran susunan lapisan tanah dan kekuatannya, menentukan kedalaman dan ketebalan lapisan tanah yang berpotensi likuifaksi dan penurunan lapisan tanah akibat likuifaksi. Analisis potensi likuifaksi dilakukan menggunakan data CPT (cone penetration test) dan N-SPT (standard penetration test), dengan mempertimbangkan nilai percepatan getaran tanah maksimum (p.g.a) sebesar 0,25g, magnitudo gempabumi sebesar 6,2 SR dan muka airtanah setempat. Hasil penyelidikan menunjukkan bahwa lapisan tanah lepas selama gempabumi terdiri dari pasir lanauan dan lanau pasiran pada kedalaman antara 0,2 -12,8 m. Analisis potensi likuifaksi mengindikasikan bahwa ketebalan lapisan tanah yang berpotensi terlikuifaksi bervariasi antara 0,2 m dan 5,2 m, Sedangkan penurunan total lapisan tanah terutama terkonsentrasi di wilayah bagian tengah yang terletak di jalur Patahan Opak dengan besaran antara 0,21 cm hingga 12,98 cm.
-An assessment of surface rupture and collateral ground failures can help to evaluate the impact of future earthquakes. This paper presents the results of a field survey conducted to map the surface rupture and geotechnical phenomena associated with the ground shaking during the July 2, 2013 earthquakes in Tanah Gayo Highland. The objectives of this survey are to document and to characterize the surface ruptures as well as to identify types of earthquake-induced ground failures. Results of the survey identified four best sites of possible surface rupture. Two locations are obvious surface ruptures that can be traced on primary topographic feature of the active fault segment from the north to the south, crossing Pantan Terong Hill. The fault segment has a total mapped length of 19 km, with WNW trending zone and a dextral rupture offset. The ground shaking also resulted in landslides and liquefaction in areas underlain by very fine-grained tuffaceous sands. Based on the field survey, it can be concluded that the newly defined active fault segment, the Pantan Terong segment, is likely the segment that ruptured at the July 2, 2013 Tanah Gayo earthquake. Due to the soil types and unstable rocky slopes in the hilly Central Aceh region, large-scale landslides are primary risks during an earthquake event in this region.
A landslide susceptibility mapping is essential for landslide hazard mitigation to reduce the associated risk. This paper aims to present the results of the landslide susceptibility modeling in the Citarik sub-watershed using three bivariate statistical-based methods, i.e., frequency ratio (FR), information value (IV), and weight of evidence (WoE). The main objective of this study is to evaluate the significance of the threshold of the area under curve (AUC) value in parameter selection. In this study, 118 landslide pixels were compiled from Google Earth images, unmanned aircraft vehicle (UAV) aerial photos taken just after the landslide, official landslide reports, and field observation. Thirteen landslide causative factors were prepared in Geographic Information System (GIS) environment, derived from various satellite images and maps. The landslide data were divided into two groups, 70% of data as training data and the rest as test data. Two scenarios that involve a different number of parameters were compared to explain the threshold of the AUC value in parameter selection and model accuracy. The result of this study shows that the AUC value threshold of 0.6 for parameter selection cannot be applied in all cases, and the performance of both two scenarios was excellent in assessing landslide susceptibility in this study area. Those three landslide susceptibility zonation maps of the best scenario showed that the sub-watershed's northern, northeastern, south-eastern, and southern parts were under high to very high susceptibility to landslides, including the Cimanggung area where a recent deadly double landslide occurred.
The September 30, 2009 Padang earthquake has resulted in damages to infrastructures and buildings and a death toll of 383 in Padang City. Numerous liquefaction and ground deformations caused by the earthquake were particularly evidence in the areas few kilometers from the coast. The paper presents results of the previous field geotechnical investigations of liquefaction potential and the recent liquefaction observations in Padang City. A microzonation map was created using the data from liquefaction potential analyses and liquefaction potential indexes. The predicted liquefaction susceptibility zones showed a good agreement with site observations. The assessment suggests that the liquefaction susceptibility decreases to the northeast away from the coastal line.
Pengetahuan mengenai kerentanan likuifaksi di suatu wilayah kota pesisir yang rawan gempabumi besar sangat diperlukan dalam perencanaan tataruang untuk mengurangi bencana seismik. Makalah ini menyajikan hasil evaluasi potensi likuifaksi di wilayah Kota Banda Aceh berdasarkan metode uji penetrasi konus untuk menghasilkan mikrozonasi kerentanan penurunan lapisan tanah akibat likuifaksi di wilayah ini. Hasil analisis menunjukkan bahwa potensi likuifaksi terdapat pada lapisan tanah pasir dan campuran pasir dan lanau, yang dicirikan oleh nilai tahanan konus dan hambatan setempat masing-masing lebih kecil dari 15 MPa dan 150 kPa pada kedalaman dan ketebalan yang bervariasi. Berdasarkan hasil perhitungan penurunan tanah, wilayah Banda Aceh dapat dibagi menjadi lima zona kerentanan. Zona kerentanan tinggi terutama terdapat di Kecamatan Kuta Alam dan Syah Kuala, sedangkan zona kerentanan rendah terutama terdapat di wilayah Kecamatan Banda Raya. Dengan demikian, investigasi geoteknik detil sangat diperlukan untuk mencegah kerusakan pada bangunan dan infrastruktur akibat likuifaksi di wilayah Kota Banda Aceh.
Pusat Penelitian Geoteknologi LIPI ABSTRAK Prediksi bahaya gerakan tanah secara spasial dan temporal diperlukan untuk mitigasi bencana gerakan tanah. Makalah ini bertujuan untuk menyajikan hasil pemodelan tingkat kerentanan gerakan tanah dengan mempertimbangkan karakteristik lereng dan kekuatan tanah secara spasial dan curah hujan harian secara temporal di wilayah Kabupaten Sukabumi. Pemodelan menggunakan perangkat lunak TRIGRS untuk menghitung faktor keamanan lereng berbasis grid dengan ukuran 100 m x 100 m akibat infiltrasi air hujan. Hasil pemodelan menunjukkan tingkat kerentanan gerakan tanah spasial di Kabupaten Sukabumi dipengaruhi oleh topografi dan karakteristik keteknikan tanah. Sementara itu, curah hujan kumulatif menjadi faktor pengontrol penyebab perubahan tingkat kerentanan gerakan tanah temporal. Berdasarkan nilai faktor keamanan lereng, daerah dengan kerentanan gerakan tanah
Daerah Cekungan Bandung tersusun oleh endapan aluvial yang terdiri atas lapisan lempung dengan sisipan lapisan pasir yang belum mengalami pemadatan sehingga mempunyai potensi likuifaksi. Makalah ini menyajikan hasil analisis potensi likuifaksi di wilayah Cekungan Bandung berdasarkan data Standard Penetration Test (SPT) dengan mempertimbangkan percepatan tanah puncak akibat gempa bumi Sesar Lembang (Mw 6,5) dan akibat gempa bumi subduksi (Mw 7,0). Hasil analisis menunjukkan bahwa potensi likuifaksi terjadi pada lapisan pasir di kedalaman yang bervariasi dan pengaruh percepatan tanah puncak terhadap potensi likuifaksi akibat gempa bumi Sesar Lembang lebih besar daripada gempa bumi subduksi. Mempertimbangkan ketebalan lapisan pasir, penurunan tanah total akibat likuifaksi dapat mencapai 40,66 cm akibat gempa bumi Sesar Lembang dan penurunan tanah total hingga 26,08 cm akibat gempa bumi di zona subduksi.
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