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On November 21, 2022, the Cianjur area in West Java, Indonesia, experienced devastating landslides caused by a magnitude 5.6 earthquake, with the epicenter traced to a hidden active fault approximately 11 kilometers beneath the surface, known as the Cugenang Fault. This study investigates the post-disaster landslides and aims to discover the characteristics of the landslides triggered by this earthquake. The methodology involves literature review, lithology descriptions, landslide slip surface analysis, soil analysis, slope assessment, land cover and land use change examination, landslide orientation evaluation, and distance measurements to the earthquake's epicenter and the Cugenang fault. Drones aided spatial landslide analysis. The study highlights the strong link between intense shaking along the active fault and landslide occurrences. Due to lithological bedding control, these landslides all head southwest and are located 0.35 to 0.67 kilometres from the fault. The residual soil, highly weathered breccia, and possible tuff volcanic deposits, which act as a sliding plane, lie in a similar direction to the slope, creating a vulnerable setting for landslides. The morphology and exposures of the Sarampad and Rawacina landslides showed similar phenomena to liquefaction. Land use changes, including slope cutting without proper stabilization measures, contribute to landslides to a certain degree.

Understanding the occurrence of flow liquefaction requires knowledge of the sub-surface condition controlling its occurrence. This paper presents the results of seismic refraction surveys conducted to evaluate the sub-surface geological condition in the Sibalaya flow liquefaction area. From the interpretation of the seismic refraction model, an inclined boundary presents between the near-surface sediment layers. Further examinations of the SRT images demonstrate the existence of localized basinal structures in the rock layer with the highest P-wave velocity. The basinal structure may be associated with a hidden normal fault system of horst-graben structures. Thus, this study indicates that such a complex sub-surface geological structure also contributed to the Sibalaya flow liquefaction occurrence.

The occurrence of flow liquefaction phenomena, locally termed Nalodo, during the Donggala-Palu earthquake on 28 September 2018 destroyed some residential areas and infrastructures in Palu City and Sigi Regency. Evaluation of liquefaction potential in the flow liquefaction areas is required to assess the liquefaction susceptibility of the area to future earthquakes. This paper presents the results of liquefaction potential analysis in the Balaroa, and Petobo areas based on the SPT method. A calculated peak ground acceleration was used for each location. Based on the analysis, all the liquefied soil layers are still liquefiable, especially in the Balaroa area, causing a significant ground settlement. These results imply that flow liquefaction areas are still susceptible to liquefaction during a big earthquake event. Thus, restriction of re-inhabitants in the liquefaction areas is necessary, and the infrastructure development in the areas requires a proper engineering design to mitigate earthquake-induced liquefaction hazards in the future.

Gunung Batu is placed in Lembang, Langensari, West Bandung right of Lembang Fault line. Lembang Fault is an active fault with a slip rate between 1.95 – 3.45 mm/year and is expected to initiate an earthquake of Mw 6.5 – 7. Earthquakes in the Lembang Fault zone occurred in the 15th and 60th centuries BC, with an earthquake cycle every 170 – 670 years. From this, earthquake cycle estimates indicate that the Lembang Fault is in the final stage of the earthquake cycle. Gunung Batu is a populous area and has grown as a recreational area. Gunung Batu has a complex geological structure with potential rock slides. The observation and kinematic analysis results of the Gunung Batu area suggested that this area partly has an unstable slope and potentially has wedge and toppling failure. This condition of instability requires further monitoring to minimize damage and losses to populations around the Gunung Batu area. The development of slope stability monitoring tools has progressed significantly recently. Selecting the proper monitoring tool is the main component of data input to prevent possible hazards. The monitoring elements include rainfall, slope movement, and tilt movement. Sensor types that will be used in this monitoring system are integrated wireless monitoring systems. This system was developed to monitor the activity of the slopes of Gunung Batu, Lembang, West Bandung. The monitoring results for the last six months show the system is running well without errors.

Critical lands are formed after landslides due to the erosion and stripping of the surface soil in the depletion zone and the formation of accumulation zones, requiring remediation efforts. Indigenous arbuscular mycorrhizal fungi help rehabilitate degraded lands, including post-landslide sites, by adapting to native soil conditions. This study investigates mycorrhiza’s presence in post-landslide areas with sandy silt in Cililin and clayey silt in Citatah. Soil samples are collected at 30 cm depth using a corer near Dysoxylum macrocarpum in Citatah and Gmelina arborea in Cililin. Mycorrhiza isolation involves wet sieving and centrifugation. Local mycorrhiza genera identified are Glomus, Gigaspora, Acaulospora, and Scutellospora. Sandy silt soil 2 exhibits the highest spore density of 178 per 100 grams, while clayey silt soil 1 has the lowest density of 148 per 100 grams. Glomus dominates in sandy silt with a 93 per 100 grams concentration and a 38–45 µm size. Scutellospora is scarce in clayey silt, with only 1 per 100 grams, 90-170 µm size. Isolated mycorrhiza can serve as compatible and adaptive inoculum. The discovery of mycorrhiza tolerant to post-landslide conditions is expected to play an important role in the remediation process of critical lands caused by landslides.

Copyright of Rudarsko-Geolosko-Naftni Zbornik is the property of Faculty of Mining, Geology & Petroleum Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

On 28 September 2018, a strong earthquake (Mw 7.5) struck Donggala Regency triggering flow liquefaction (locally termed Nalodo) phenomena in two residential areas in Palu City. Mitigating such an earthquake collateral hazard requires understanding the geological condition controlling such liquefaction. This paper presents a geophysical study to clarify the geological condition controlling the Nalodo phenomena in Palu City. The objectives of this study were to estimate shear wave velocity (Vs) profiles in the Nalodo and non-Nalodo sites and evaluate liquefaction potential based on the shear wave velocity profiles. The study involved a series of array microtremor surveys in two Nalodo sites and three non-Nalodo sites in Palu City. The results show that Vs generally increases with depth but varies from one site to another. Based on the Vs profiles, a thick soil layer with Vs of less than 175 m/s is present from the ground surface in the Balaroa and Petobo sites. Contrary, this soil layer is detected at a deeper depth in the non-Nalodo sites. Based on the liquefaction potential analysis, the near-surface soil layers in the Balaroa and Petobo sites are clearly liquefiable for all the PGA values used in this study. Although deeper soil layers can also be liquefied, no liquefaction occurred in non-Nalodo sites because a thick medium soil layer exists near the surface. Thus, a thick soil layer with Vs of less than 175 m/s near the ground surface controls the Nalodo phenomena in Palu City. Further studies to clarify other factors controlling flow liquefaction are recommended.

The 7.4 Mw earthquake on 28th September 2018 in Palu City triggered a flow liquefaction phenomenon in the Balaroa and Petobo areas, contributing to significant casualties and building damage. This paper presents the results of a liquefaction study to map subsurface conditions in these areas using the multi-electrode resistivity method with the dipole-dipole configuration. The objective of this study is to understand factors controlling the flow liquefaction phenomenon. Based on the interpretation of 2-D resistivity images, the liquefied soil layers are characterized by lower resistivity values than the non-liquified layers. These contrasts of resistivity values form a gently sloping boundary between the liquefied and non-liquefied soil layers. The resistivity image perpendicular to the flow direction indicates the presence of a subsurface basinal morphology in the Balaroa area, suggesting that a shallow groundwater zone is present within the liquefiable soil layer. Thus, the subsurface topographical condition is the main governing factor of flow liquefaction phenomena during the 2018 Palu earthquake.

Copyright of Rudarsko-Geolosko-Naftni Zbornik is the property of Faculty of Mining, Geology & Petroleum Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The magnitude 7.6 MW earthquake that occurred on 30 September 2009 in West Sumatera caused significant damages to buildings in the city of Padang related to the phenomenon of amplification and liquefaction. This paper presents the results of the assessment and mapping of amplification and liquefaction, carried out in the coastal area of Padang City. Mapping of soil amplification was carried out in 250 locations using the HVSR microtremor method. Meanwhile, evaluation of the potential for liquefaction was carried out in 95 locations using a cone penetration test-based method. Based on the analysis, Padang City has five seismic susceptibility zonations. Coastal areas, including the sub-districts of Koto Tangah, North Padang, West Padang, and South Padang, are located in high to very high susceptibility to soil amplification and liquefaction. These results are in agreement with the phenomenon of building damage due to amplification and liquefaction during the 2009 earthquake.

The development of a physically based warning system for rainfall-induced slope failures requires a comprehensive understanding of the failure process. A set of laboratory-scale soil slopes was subjected to instability, through three different modes of raising water level, to clarify the process of failure initiation. Hydrologic responses of the model slopes to the saturation process were recorded by volumetric soil moisture content sensors. The results of model tests show that failures of the model slopes were essentially initiated by the development of an unstable area near the slope toe, upon the formation of the seepage area, with shallow noncircular sliding being the dominant failure mode. The volumetric moisture content of the slope region where localized failures initiated was noted to reach a nearly saturated value. However, the major portion of soil slopes involved in overall instability was still in an unsaturated condition. Based on the observed moisture content response of the model slopes, a concept for prediction methodology of rainfall-induced slope failures is introduced. DOI: 10.1061/(ASCE)1090-0241(2007)133:5(575) CE Database subject headings: Laboratory tests; Landslides; Moisture content; Predictions.