Using Ambient Noise Attenuation and Surface Tomographies to investigate Lusi, Indonesia. From a natural disaster to a geothermal opportunity.

We deployed a network of temporary stations to invert passive seismic data to compare the intrinsic attenuation distribution and the S-wave velocity structure of a region of the Kendeng Basin in east Java, Indonesia. This geological domain hosts the Lumpur Sidoarjo, nicknamed Lusi, that is the eruptive centre of the sediment-hosted geothermal system that pierced the Earth's surface in May 2006. To date, Lusi is the youngest onshore hybrid system on Earth. We show that ambient noise and intrinsic attenuation tomographies are complementary tools that should be performed routinely when studying geothermal systems.

Our study highlights that Lusi's plumbing system features two distinct fluid flow regimes, one across the shallow sedimentary units and one developing sub-vertically across the deeper domains of the basin. Historically, this region is considered an hydrocarbon province as shown by the  dozens of wells extracting hydrocarbons form the gas reservoirs. However, we show that such a basin is also rich in geothermal resources and the well facilities could be re-purposed for the exploitation of geothermal resources. This is particularly timely since the hydrocarbon extraction of the gas fields is declining and the energy transition is becoming more and more pressing. The high geothermal gradient, the steep topography of the nearby volcanic arc, as well as the well-studied subsurface all combine to make this portion of the Kendeng basin an excellent geothermal site. We strongly recommend that future geothermal operators capitalise on the existing infrastructures and transform the natural disaster of Lusi into a geothermal opportunity.