1Berita English – The Meteorology, Climatology, and Geophysics Agency (BMKG) has successfully identified a new fault named the Sumedang Fault as the culprit behind the Sumedang earthquake on December 31, 2023. This new fault is said to have not been mapped before.

The Sumedang region was previously hit by an earthquake with a magnitude of M4.8, located at coordinates 6.85 degrees S and 107.94 degrees E, precisely on land 2 kilometers northeast of the center of Sumedang City, West Java, with an earthquake depth (hypocenter) of 5 kilometers from the Earth’s surface.

According to BMKG’s analysis, the earthquake began with two foreshocks, occurring at 2:35 PM with a magnitude of M4.1 and at 3:38 PM with a magnitude of M3.4. It was then followed by several aftershocks with magnitudes ranging from M2.4 to M4.5.

BMKG states that this earthquake is a shallow crustal earthquake caused by the activity of an active fault, with a source mechanism resulting from a combination of horizontal and upward movements (oblique thrust fault), trending in a north-south direction.

“Considering the distribution of aftershocks, tectonic settings, and source mechanism analysis, the earthquake was caused by an Active Fault passing through Sumedang City, which was initially unmapped, and according to BMKG seismicity data analysis, it is called the Sumedang Fault,” said BMKG Head Dwikorita Karnawati in a statement on Monday (1/8).

Dwikorita explained that the Sumedang Regency is a seismic-prone area with earthquake sources originating from the collision zone of the Indo-Australian and Eurasian plates in the Indian Ocean. In addition, earthquakes also come from several active faults on land that have been mapped, such as the Cimandiri Fault, Cugenang Fault, Lembang Fault, Cipamingkis Fault, Garsela Fault, Baribis Fault, Cicalengka Fault, Cileunyi-Tanjungsari Fault, Tomo Fault, and Cipeles Fault, as well as several other unmapped active faults.

Meanwhile, according to the BMKG Damaging Earthquake Catalog (2020), continued Dwikorita, the Sumedang region had experienced damaging earthquakes twice before, on August 14, 1955, causing extensive building damage, and on December 19, 1972, with a magnitude of M4.5, resulting in building damage and landslides.

“The earthquake that occurred on December 31, 2023, was not only felt in Sumedang Regency and Bandung Regency but also felt as far as Bandung City, Sumedang Regency, and Garut Regency,” said Dwikorita.

Furthermore, Dwikorita said that BMKG is coordinating with the Sumedang Regency Regional Disaster Management Agency (BPBD), the National Disaster Mitigation Agency (BNPB), Search and Rescue (SAR), and the Ministry of Social Affairs to reassure residents by providing earthquake literacy/education, as well as steps for earthquake mitigation and self-rescue before, during, and after earthquakes.

BMKG has also conducted surveys and various studies, including seismicity surveys, macroseismic surveys, microzonation surveys, deformation surveys, aerial photography with lidar, morphotectonic evaluations, and subsurface fault structure surveys.

“These surveys are conducted to map earthquake activity and distribution and to understand in detail the main causes of the earthquake, including identifying and validating fault paths,” said Dwikorita.