NEW research concludes that a major mud volcano disaster in Indonesia was not triggered by an earthquake but was instead the consequence of nearby gas drilling operations.
A mud volcano suddenly opened up in the city of Sidoarjo in East Java, Indonesia, in May 2006. Nine years later the eruption continues – having buried more than 6.5km2 of the city in up to 40m of mud and displacing almost 40,000 people. Costs of the disaster are estimated at over US$2.7 billion.
"Our new research essentially disproves all existing earthquake-triggering models."
Results of new research published today in the journal Nature Geoscience directly address the ongoing controversy over the cause of the disaster, says lead author Dr Mark Tingay, Adjunct Associate Professor with the University of Adelaide's Australian School of Petroleum.
“There has been intense debate over the cause of the mud volcano ever since it erupted,” Adjunct Associate Professor Tingay says. “Our new research essentially disproves all existing earthquake-triggering models.”
The study by Dr Tingay and colleagues in the United States and United Kingdom is the first to use physical data collected in the days before and after the earthquake, rather than models and comparisons.
Satellite image of the Lusi mud volcano and the buried city of Sidoarjo in March 2007. The image covers approximately 1200 by 600 meters. Photo courtesy of Lapindo Brantas.
Dr Tingay says the earthquake-trigger theory proposes that seismic shaking induced liquefaction of a clay layer at the disaster location.
“Clay liquefaction is always associated with extensive gas release, and it is this large gas release that has been argued to have helped the mud flow upwards and erupt on the surface,” he says. “However, we examined precise and continuous subsurface gas measurements from the adjacent well and show that there was no gas release following the earthquake."
According to the research released today, the Banjar Panji (BJP-1) well was located just 150m from what became the main vent of the Lusi mud volcano. The well was uncased from 1,090 to 2,833m depth and was therefore directly open to fluid exchange with almost the entire thickness of the clay layer that caused the mud.
A range of gas measurements, including gas concentration and composition were taken continuously during the drilling operation, starting from March 2006 until the day of the Lusi mud eruption on 29 May, 2006.
Factories buried in mud by the Lusi mud flow, with the Lusi main vent in the background. The Lusi mud volcano has buried over 11,000 buildings and cost over US$2.7 billion in damages and disaster management. Photo courtesy of Mark Tingay.
Associate Professor Tingay says the rocks showed no response to the earthquake, indicating that the earthquake could not have been responsible for the mud flow disaster.
“The measurements highlight that the onset of underground activity preceding the mud eruption only started when the drilling ‘kick’ occurred, strongly suggesting that the disaster was initiated by a drilling accident,” he said.
His research team also used gas signatures from different rocks and the mud eruption itself to 'fingerprint' the initial source of erupting fluids and found that erupting fluids were initially sourced from a deep formation, which is only predicted to occur in the drilling-trigger hypothesis.
“Taken together, our data strongly supports a man-made trigger. We hope this closes the debate on whether an earthquake caused this unique disaster," Associate Professor Tingay says.
Stratigraphy, BJP-1 borehole design (protective casing diameters in inches) and measured gas amounts encountered by the well.Liquefaction of the Kalibeng clay layer should generate extensive gas release, yet no increased gas flux is observed in the 24 hours after the Yogyakarta earthquake. The position of the BJP-1 drill string and drill bit at time of the drilling kick is highlighted in red.