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On 22 February 2018 at 08:00 am, a landslide occurred in the dense conserved forest area of the Cigunung Sub-River Basin at Pasir Panjang Village, Brebes Regency of Central Java Province, Indonesia. The landslide materials transformed into debris and flowed down along the river channel rapidly with a distance of more than 2 km, causing 18 people dead and 14 people injured. About 8.5 ha of farm fields, two bridges, 507 m of the provincial road, and 25 houses were destroyed due to the impact of debris flow. This paper reports the site investigation of Pasir Panjang landslide conducted in early June 2018 which covers geological on-site measurement, soil sampling for laboratory tests, and mapping using the unmanned aerial vehicle. Results imply that the source of Pasir Panjang landslide came from a highly weathered layer of volcanic breccia which fails from a steep slope. The landslide materials then entrained weathered tuffaceous sandstone and volcanic breccia layers along the river bank. Hydro-meteorological data shows that the two series of antecedent rainfalls in 10 consecutive days may generate the excess pore water pressure and high saturation condition within the landslide and debris flow area. The balancing depth of saturated soil layer then calculated to estimate the pore water pressure by using the slope infiltration distributed equilibrium model at each time interval of rainfall. We used the LS-RAPID numerical model to simulate the integration of failure mechanism of Pasir Panjang landslide and its debris motion behavior. The simulation results show that the slope fails from the unstable area of approximately 28,000 m2 with the velocity around 13–14 m/s and the maximum depth of 25–26 m. The landslide materials transformed into debris when hit the provincial road with the velocity of more than 30 m/s and traveling down rapidly to the farm field and civilization area. From this study and investigation, we concluded the enlarging volume, flow velocity, and long traveling of the debris materials of Pasir Panjang landslide controlled by the steep slope topography, highly weathered volcanic breccia, and saturated layers in the vicinity of the river and farm field area. [ABSTRACT FROM AUTHOR]

This paper presents rainfall-induced landslide thresholds and predicts landslide hazard in Kuala Lumpur metropolitan city and surrounding areas. Landslide events from 2000 to 2012 were collected. The long and short antecedent rainfall days were prepared for landslide and non-landslide days simultaneously. First, threshold analysis was conducted by using data obtained from rainfall stations located in highly urbanized areas of Kuala Lumpur metropolis. Six rainfall gauges were selected, and the study area was divided into six zones according to rainfall gauges: Taman Desa Station (TD-KL), Genting Klang (GK-KL), LDG Edinburgh Station (LDGE-KL), SG Raya Hulu Langat Station (SRHL-Slg), Puchong Drop Station (PD-Slg), and Bukit Antarabangsa (BTA-Slg). After the threshold analysis was conducted for different periods (10, 15, and 30 days) in each station, reliability index test was conducted to optimize the best threshold that limits the predicted events along the study period for each region. Second, the threshold analysis results were used as input in the Poisson probability model to estimate landslide temporal probability ( P). Third, the spatial probability ( P) analysis was prepared by using the evidential belief function multiplied by the P to obtain the hazard maps for 1-, 3-, and 5-year scenarios. Finally, a validation process was conducted to test the prediction performance of the resultant hazard map for a 1- and 2-year prediction by using the landslide inventory of 2012 to early 2014, which was not included in the modeling of the hazard map. Results showed a valid correlation between the high and moderate hazardous areas for the six zones. The predicted hazard maps indicated a quantitative assessment of the prone areas and proved to be a valid disaster management tool. The produced hazard maps may play a vital role as input component in risk analysis. [ABSTRACT FROM AUTHOR]

The intensity-duration (I-D) threshold is considered an effective indicator for landslides triggered by short-term high-intensity rainfall and long-term low-intensity rainfall. However, previous studies have not considered the influence of antecedent rainfall. Herein, we analyzed hourly rainfall data for 613 shallow landslides that occurred from 1963 to 2018 in South Korea to obtain rainfall thresholds and investigated the effect of antecedent rainfall conditions on threshold variations. The I-D and IMAP-D, which is normalized by dividing I by mean annual precipitation (MAP), thresholds were determined to be I = 10.40D–0.31 and IMAP = 0.006D–0.26 (4 ≤ D (h) ≤ 84), respectively, at the 2nd percentile level through quantile regression analysis. These thresholds were lower than other local thresholds (i.e., excluding global and regional thresholds), suggesting that the southern region of the Korean Peninsula was more susceptible to rainfall-induced landslides. Although the effective length of antecedent rainfall was not presented herein, the I-D threshold of landslide-triggering rainfall was confirmed to be low for the absolute and/or calibrated antecedent rainfalls greater than event cumulative rainfall at 5, 7, 10, and 20 days prior to the event. Such differences in I can be greater at shorter durations; however, these differences gradually decrease as D increases, suggesting that they lose their effect as soil water content increases. The results of the current study can improve the understanding of the effect of antecedent rainfall conditions on landslide occurrence and should be further tested with respect to the hydrologic response of hillslopes by considering regional climate and local site conditions. [ABSTRACT FROM AUTHOR]