A series of earthquakes occurred at the northern part of Lombok Island during July–September 2018 with the highest Mw7.0 5th August 2018 that caused the death of hundreds of people and ruined thousands of buildings. The earthquakes were triggered on the Flores Thrust located at the back arc zone and at only 50 km distance from the island, leading to multiple seismic hazards to Lombok and surrounding islands. The thrust could possibly be the dominant current seismic sources; however, the megathrust sources also contributed to the hazards due to the subduction between the Indo-Australia and Eurasia tectonic plates in the Nusa Tenggara region. An updated probabilistic seismic hazard analysis was, therefore, conducted on recent seismicity, detailed tectonic background, and suitable ground motion prediction equations, to determine higher seismic parameter values than the 2017 models. This means that Lombok and surrounding islands exposed to higher seismic hazards than those predicted before the earthquake events in 2018.
The Luk Barat Bridge has an important role in transportation infrastructures in the North Lombok District, connecting cities in Lombok Island. Unfortunately, the bridge is located where the most vulnerable area in Lombok Island, as earthquakes occurred in 2018 have ruined almost one third of the island and destroyed thousands of buildings. The bridge has been deformed after the earthquakes. Geodetic measurement showed that the bridge has displaced in total of 0.36 m measured from the datum point of BM2 near located closed to the bridge area. Numerical modeling also indicated a similar value of displacements.
DOI:10.17014/ijog.9.1.105-117A series of earthquakes in 2018 have ruined thousands of buildings, and affected the stability of many infrastructures in Lombok Island. The Meninting dam, located at just a 20 km distance from the epicentre of the 5th August earthquake, is one of the many infrastructures being constructed in the island. Unfortunately, stability problems might arise to the dam, in particular to its diversion-spillway tunnel, since the tunnel was designed by using the Indonesian Standards SNI 1726:2012 for the estimation of earthquake forces into the design. After the earthquake events in 2018, seismic conditions of Lombok Island changed, resulted in changing seismic parameters. Seismic forces might shear off the friable weak volcanic rocks around the tunnel, and then consequently, the residual strength of the rocks had to stand the tunnel construction, so its factor of safety reduced. Thus, the tunnel required some stability improvements by adding more support instalments, including grouting and rock bolting. This is important for the tunnel to face probable similar severe earthquakes in the future.
The Pandan Duri dam has an important role in water supply in the East Lombok District. Unfortunately, Lombok Island is located in a relatively high seismic risk area, as earthquakes occurred in 2018 have ruined almost one third of the island and destroyed thousands of buildings. The Pandan Duri dam is one of many infrastructures shacked by the earthquake. Modelling the dam shows that the grouting installation of the dam has supported the dam after the earthquake. The factor of safety (FoS) of the dam was still 1. 76 after the earthquake for the flood water level conditions; but, the displacements could be significant to the stability of the dam, as the dam might displace up to 1. 64 m. Although, the current grouting support system might provide the stability to the dam during earthquake events, the dam will certainly require further stability enhancement and close monitoring for possible similar events in the future.
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