M 7.0 SR Earthquake in North Lombok, Nusa Tenggara Barat

The earthquake occurred on Sunday, August 5, 2018, at 18:45:35 WIB. Based on information from BMKG the epicenter was at coordinates 8.37° South Latitude and 116.48° East Longitude, with a magnitude of 7.0 at a depth of 15 km. Previously, on July 29, 2018 with the power of M6.4 with a depth of 10 km.

This earthquake caused severe damage in North Lombok and East Lombok regencies and was based on information from BNPB until the death toll from the earthquake reached 105 people. The Geology Agency sent the Earthquake Emergency Response Team and the Land Movement to the location to map the impact of the earthquake, especially related to geological damage. The Emergency Response Team found soil cracks and landslides on the road that connecting Pemenang, Tanjung and Gangga Districts, North Lombok District. Liquefaction or leaching is also found in the Gangga area. Ground cracks and movements also occur in Sambelia District and Sembalun Sub-District, East Lombok Regency, especially on the slopes and around the climbing lanes of Rinjani Volcano and other steep hills. These ground cracks and movements were triggered by the earthquake of July 29, 2018, which was further aggravated by the shock of the August 5, 2018 earthquake.

Based on the results of the field survey and analysis of the Geological Agency Emergency Response Team, the two earthquakes that have occurred have the same mechanism associated with the Flores Naik Busur Belakang Fault located in the north of Lombok Island.

Earthquake Prone Areas Map (KRB) Earthquakes published by PVMBG-Geological Agency, North Lombok and East Lombok areas including KRB Middle Earthquakes, with potential earthquakes with intensity VII-VIII MMI (Modified Mercalli Intensity), which potentially cause damage . The results of mapping the impact of the earthquake show that the intensity of earthquake shocks in North and East Lombok is VII – VIII MMI.

The area affected by the earthquake is a difficult area of water, so in some places refugees lack water. BPBD and volunteers supply water using tank cars, and one of them is the result of drilling the Geology Agency. One of the completed drill wells is in Rempek Village, Gangga district, North Lombok. The Geological Agency team is looking for another location that has the potential for water to be drilled to be used as a water source to supply refuge sites.

Recommendation

Based on the results of field examinations and analyzes related to potential dangers going forward, the Geological Agency provides recommendations as follows:

1. The citizen is encouraged to stay calm and follow instructions and information from the regional government and the NTB BPBD. Don’t be provoked by irresponsible issues regarding the earthquake and tsunami.
2. Aftershocks usually have smaller magnitudes than the main earthquake, but people are expected to remain vigilant. Buildings that have suffered medium to severe damage should not be inhabited because aftershocks are still frequent and can worsen damage.
3. For those in hilly areas and around steep slopes it is advisable to remain vigilant not to carry out activities around the location of cracks and steep slopes because aftershocks still have the potential to trigger ground movements. Precautions need to be increased if there is high intensity rain in the hilly area, because the water can fill cracks which then potentially trigger land movement events.

Source : Rudi Suhendar Head of the Geology Agency