Soil gas anomalies along the Watukosek fault system, East Java, Indonesia.

Sciarra, Alessandra, Ruggiero, Livio, Bigi, Sabina and Mazzini, Adriano (2017) Soil gas anomalies along the Watukosek fault system, East Java, Indonesia. Open Access [Talk] In: AGU Fall Meeting 2017. , 11.12 - 15.12.2017, New Orleans, USA .

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Two soil gas surveys were carried out in the Sidoarjo district (East Java, Indonesia) to investigate the gas leaking properties along fractured zones that coincide with a strike-slip system in NE Java, the Watukosek Fault System. This structure has been the focus of attention since the beginning of the spectacular Lusi mud eruption on the 29th May 2006. This fault system appear to be a sinistral strike-slip system that originates from the Arjuno-Welirang volcanic complex, intersects the active Lusi eruption site displaying a system of antithetic faults, and extends towards the NE of Java where mud volcanic structures reside. In the Lusi region we completed two geochemical surveys (222Rn and 220Rn activity, CO2 and CH4 flux and concentration) along four profiles crossing the Watukosek fault system. In May 2015 two profiles ( 1.2 km long) were performed inside the 7 km2 embankment area framing the erupted mud breccia zone and across regions characterized by intense fracturing and surface deformation. In April 2017 two additional profiles ( 4 km long) were carried out in the northern and southern part outside the Lusi embankment mud eruption area, intersecting the direction of main Watukosek fault system. All the profiles highlight that the fractured zones have the highest 222Rn activity, CO2 and CH4 flux and concentration values. The relationship existing among the measured parameters suggest that the Watukosek fault system acts as a preferential pathway for active rise of deep fluids. In addition the longer profiles outside the embankment show very high average values of CO2 (5 - 8 %,v/v) and 222Rn (17 - 11.5 kBq/m3), while soil gas collected along the profiles inside the Lusi mud eruption are CH4-dominant (up to 4.5%,v/v).This suggests that inside the embankment area (i.e. covered by tens of meters thick deposits of erupted mud breccia) the seepage is overall methane-dominated. This is likely the result of microbial reactions ongoing in the organic-rich sediments producing shallow gas that gets mixed with deeper rising fluids. In contrasts profiles collected in areas not covered by the organic rich mud breccia, and that are crossing the main Watukosek fault system, have the highest 222Rn activity and CO2 concentration values. We suggest that at these localities the rise of deep fluids is not affected by shallower gas production.

Document Type: Conference or Workshop Item (Talk)
Projects: FLOWS
Date Deposited: 14 May 2018 12:36
Last Modified: 14 May 2018 12:36

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