PROCJENA PODLOŽNOSTI NA KLIZIŠTA INICIRANA POTRESOM: POTRES OD 7,5 MW U 2018. GODINI U PALUU, SULAWESI, INDONEZIJA

A catastrophic Palu earthquake on September 28th, 2018 with Mw 7.5 triggered countless slope failures, generating numerous landslides. This paper presents a practical method for susceptibility assessment of earthquake-induced landslides in the Palu region and the surrounding area. The statistical weight of evidence (WoE) model was used to assess the relationship between landslides induced by seismic motion and its causative factors to determine the susceptibility level and derive an earthquake-induced landslide susceptibility map of this study area. The 1273 landslides were classified into two data series, training data for modelling (70%) and test data for validation (30%). The six selected thematic maps as landslide causative factors are lithology, land use, peak ground acceleration (PGA), and slope (gradient, aspect, elevation). The selection of causative factors considerably influences the frequency of landslides in the area. The result is satisfactory because the AUC value of the chosen model excelled the minimum limit, which is 0.6 (60%). The estimated success rate of the model is 85.7%, which shows that the relevancy of the model is good with the occurrence of landslides. The prediction rate of 84.6% indicates that the applied model is very good at predicting new landslides.Katastrofalni potres koji se dogodio u Paluu 28. rujna 2018. godine, magnitude 7,5 Mw, izazvao je brojne nestabilnosti na padinama, uključujući nastanak velikoga broja klizišta. Ovaj rad predstavlja praktičnu metodu za definiranje procjene podložnosti na klizišta izazvana potresom u regiji Palu i okolnom području. Metoda Weight of Evidence (WoE) korištena je za procjenu odnosa između klizišta izazvanih seizmičkim kretanjem i preduvjeta kako bi se odredila razina podložnosti i izradila karta podložnosti na klizišta izazvana potresom u istraživanom području. 1273 klizišta podijeljena su u dvije serije podataka: podatci za treniranje modela (70 %) i podatci za validaciju modela (30 %). Korišteno je šest odabranih tematskih karata kao faktora koji utječu na pojavu klizišta: litologija, korištenje zemljišta, vršno ubrzanje tla (PGA), nagib padine, orijentacija padine i nadmorska visina. Odabir uzročnih faktora znatno utječe na učestalost klizišta na tom području. Rezultat modela zadovoljavajući je jer je vrijednost AUC odabranoga modela premašila minimalnu granicu koja iznosi 0,6 (60 %). Procijenjena uspješnost modela iznosi 85,7 %, što pokazuje relevantnost modela kod pojave klizišta. Stopa predviđanja od 84,6 % upućuje na to da je primijenjeni model vrlo dobar u predviđanju novih klizišta

Tectonic Model of Bali Island Inferred From GPS Data

DOI: 10.17014/ijog.5.1.81-91Seven periods of GPS campaign have been conducted for three years since March 2013 - October 2015 on fourteen GPS sites across Bali Island. The GAMIT/GLOBK 10.6 version was used to compute data with respect for thirteen reference sites of International Terrestrial Reference Frame (ITRF) 2008 surrounding Bali. The result shows that horizontal displacement varies between 1.93 and 22.53 mm/yr dominantly northeastward. Vertical displacement ranges at -184.34 to 33.79 mm/yr. The result of modeling using Coulomb 3.3 version indicates the deformation in Bali was mostly contributed by subduction at the southern part, West and East Flores Back-Arc Thrust at the north, Lombok Strait Fault and a fault at the eastern coast of Bali with the estimation maximum magnitude of 7.1, 6.6, 6.8, 5.8, and 5.2, respectively

Assessing Sensitivity of Probabilistic Seismic Hazard Analysis to Fault Parameters : Java and Sumatra Case Study

"The aim of this thesis is to study the impact of fault parameter uncertainty on seismic hazard analysis using Java and Sumatra, Indonesia, as case studies. Slip rate and fault geometry are two important inputs in determining seismic hazard, because they are used to estimate earthquake recurrence and maximum magnitude, both of which strongly influence near fault hazard levels. However, the uncertainty of slip-rates and fault geometry are rarely considered in probabilistic seismic hazard analysis (PSHA), which is surprising given that estimates of slip-rate can vary significantly from different data sources (e.g. geologic vs. geodetic). We produce PSHA maps for Java and Sumatra, and study the contribution from the crustal faults and subduction sources. We also analyse the contribution from different components of the subduction source. The importance of the regolith amplification and the method which might be best for application in Indonesia is also discussed. We use the PSHA method to assess the sensitivity of seismic hazard to fault parameters along the Sumatran Fault System (SFS) in Sumatra, Indonesia and we consider the aleatory uncertainty of fault slip by employing the logic tree tools to include epistemic uncertainty alternative slip rates. The weighting of the logic tree branches are determined by the probability density function of the slip rate estimates using the approach of Zechar and Frankel (2009). We consider how the PSHA result accounting for slip rate uncertainty differ from that for a specific slip rate by examining hazard values as a function of return period and distance from the fault. We also consider the locking width of the fault, to study the effect from different maximum magnitudes. Our study demonstrates that uncertainty in fault slip-rates, fault geometry and maximum magnitude have a significant impact on hazard level and area impacted by earthquakes and should be considered in PSHA studies.

Tectonic Model of Bali Island Inferred from GPS Data

DOI: 10.17014/ijog.5.1.81-91Seven periods of GPS campaign have been conducted for three years since March 2013 - October 2015 on fourteen GPS sites across Bali Island. The GAMIT/GLOBK 10.6 version was used to compute data with respect for thirteen reference sites of International Terrestrial Reference Frame (ITRF) 2008 surrounding Bali. The result shows that horizontal displacement varies between 1.93 and 22.53 mm/yr dominantly northeastward. Vertical displacement ranges at -184.34 to 33.79 mm/yr. The result of modeling using Coulomb 3.3 version indicates the deformation in Bali was mostly contributed by subduction at the southern part, West and East Flores Back-Arc Thrust at the north, Lombok Strait Fault and a fault at the eastern coast of Bali with the estimation maximum magnitude of 7.1, 6.6, 6.8, 5.8, and 5.2, respectively.</div

SUSCEPTIBILITY ASSESSMENT OF EARTHQUAKE-INDUCED LANDSLIDES: THE 2018 PALU, SULAWESI MW 7.5 EARTHQUAKE, INDONESIA

A catastrophic Palu earthquake on September 28th, 2018 with Mw 7.5 triggered countless slope failures, generating numerous landslides. This paper presents a practical method for susceptibility assessment of earthquake-induced landslides in the Palu region and the surrounding area. The statistical weight of evidence (WoE) model was used to assess the relationship between landslides induced by seismic motion and its causative factors to determine the susceptibility level and derive an earthquake-induced landslide susceptibility map of this study area. The 1273 landslides were classified into two data series, training data for modelling (70%) and test data for validation (30%). The six selected thematic maps as landslide causative factors are lithology, land use, peak ground acceleration (PGA), and slope (gradient, aspect, elevation). The selection of causative factors considerably influences the frequency of landslides in the area. The result is satisfactory because the AUC value of the chosen model excelled the minimum limit, which is 0.6 (60%). The estimated success rate of the model is 85.7%, which shows that the relevancy of the model is good with the occurrence of landslides. The prediction rate of 84.6% indicates that the applied model is very good at predicting new landslides