August 21, 2025 | 12:27 pm
Small-scale earthquakes are emerging from the western part of the Lembang Fault in Indonesia. From its history, the Lembang Fault earthquakes have never been significant, with magnitudes generally less than 4.
"I am one of those who do not believe that the current increase in Lembang Fault activity will result in a major earthquake," said the Professor of Structural Geology at the Faculty of Geological Engineering, Padjadjaran University (Unpad) Bandung, Iyan Haryanto, to Tempo, on Wednesday, August 20, 2025.
Iyan explained that the Lembang Fault is an earthquake fault with a length of about 30 kilometers from west to east and is divided into 3-4 segments. "This means that the risk of a major earthquake occurring is relatively lower because the fault is shorter," he said.
Nevertheless, Iyan agrees that the potential for building damage is still high. The reason is related to the geological conditions, where the rock along the Lembang Fault comes from young volcanic mountains, so its soil strength is still weak. "Without an earthquake, the soil can also landslide, let alone when there is an earthquake," said Iyan.
According to the Meteorology, Climatology, and Geophysics Agency or BMKG, there have been several earthquakes from the Lembang Fault recently, with tremors that can be felt. On July 28, 2025, there was a 2.1 magnitude earthquake, then on August 14 (M1.9), August 15 (M1.8), August 19 (M2.3), and on August 20 (M1.7).
In his inaugural speech as a Unpad Professor last Tuesday, August 19, 2025, Iyan also mentioned the Lembang Fault. From the results of his field research, he mentioned that the movement mechanism of the Lembang Fault is a normal fault or a downward fault.
"Based on the simulation results in the laboratory, a fault with such a movement mechanism can cause extensive damage compared to a horizontal fault mechanism," he said.
Based on the information in the 2017 Map of Earthquake Sources and Hazards in Indonesia, the Lembang Fault is clearly depicted in the topography as a long winding line running east-west in the northern part of Bandung City and is a continuation of the northern tip of the Cimandiri Fault. According to historical records, major earthquakes have occurred along this fault in 1699, 1834, and 1900.
"Based on geodetic studies, the fault movement rate is estimated at 6 millimeters per year at a depth of 3-15 kilometers below the surface."
According to Mudrik Daryono's research, the Lembang Fault is divided into six segments or parts. From west to east, the segments are named Cimeta, Cipogor, Cihideung, Gunung Batu, Cikapundang, and Batu Lenceng. Unlike Iyan, the mechanism of the Lembang Fault in the 2017 Map of Earthquake Sources and Hazards in Indonesia is concluded to be a left-lateral faulting with a maximum earthquake potential of magnitude 6.8.
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