Nearly three million people in Indonesia’s second city could be affected by an earthquake

Research led by a BGS scientist has revealed that an estimated 1.9 to 2.7 million people in the Bandung metropolitan region of Indonesia would be exposed to high levels of ground shaking from an earthquake on the nearby Lembang Fault.

Over the past five years, Ekbal Hussain, a remote sensing geoscientist at BGS, has worked alongside scientists in Indonesia to research and produce deformation maps for the Bandung metropolitan region. To do this, they used a combination of data from satellites and GPS measurements made around the fault.

Bandung is the capital of West Java, Indonesia, and has a population of approximately 8.4 million people. The centre of the city lies less than 10 km south of the Lembang Fault, a major fracture between two blocks of rock in West Java. Although there are no documented records of large historical earthquakes, the Lembang Fault shows geomorphological evidence of significant earthquakes in the 15th century.

A fault’s slip rate is the average amount of earthquake energy accumulation each year; using different techniques, this had previously been estimated to either be between 1.95 to 3.45 mm a year or 6 mm a year for the Lembang Fault. This new study has found that the slip rate is 4.7 mm a year.

Using this new slip rate alongside previous studies, which estimated the recurrence period of large earthquakes on the fault at between 170 and 670 years, it can be estimated that the magnitude of an earthquake will be between 6.6 and 7.0. If such earthquakes were to occur on the fault today they would expose approximately 1.9 million to 2.7 million people within the Bandung metropolitan region to high levels of ground shaking, greater than 0.3 g, or 30 per cent of the strength of gravity.

The research highlights the importance of not forgetting local crustal faults located near large urban centres, which also pose a high risk to communities.

In Indonesia, the perceived risk of earthquakes is from large events on the subduction zone. However, in this paper, we show that shorter faults like the Lembang Fault, located much closer to major cities, can also be extremely dangerous.

Ekbal Hussain, BGS Remote Sensing Geoscientist.

Funding

This is work is funded by the UK National Capability ‘Geoscience to tackle global environmental challenges’ programme. The BGS and Indonesian researchers involved in this study are continuing their engagement with local government to address the hazard challenges raised in this work.

More information

Access the full paper: The seismic hazard from the Lembang Fault, Indonesia, derived from InSAR and GNSS data