The Plumbing System Feeding the Lusi Eruption Revealed by Ambient Noise Tomography

Abstract

Lusi is a sediment‐hosted hydrothermal system featuring clastic‐dominated geyser‐like eruption behavior in East Java, Indonesia. We use 10 months of ambient seismic noise cross correlations from 30 temporary seismic stations to obtain a 3‐D model of shear wave velocity anomalies beneath Lusi, the neighboring Arjuno‐Welirang volcanic complex, and the Watukosek fault system connecting the two. Our work reveals a hydrothermal plume, rooted at a minimum 6 km depth that reaches the surface at the Lusi site. Furthermore, the inversion shows that this vertical anomaly is connected to the adjacent volcanic complex through a narrow (~3 km wide) low velocity corridor slicing the survey area at a depth of ~4–6 km. The NE‐SW direction of this elongated zone matches the strike of the Watukosek fault system. Distinct magmatic chambers are also inferred below the active volcanoes. The large‐scale tomography features an exceptional example of a subsurface connection between a volcanic complex and a solitary erupting hydrothermal system hosted in a hydrocarbon‐rich back‐arc sedimentary basin. These results are consistent with a scenario where deep‐seated fluids (e.g., magmas and released hydrothermal fluids) flow along a region of enhanced transmissivity (i.e., the Watukosek fault system damage zone) from the volcanic arc toward the back arc basin where Lusi resides. The triggered metamorphic reactions occurring at depth in the organic‐rich sediments generated significant overpressure and fluid upwelling that is today released at the spectacular Lusi eruption site.

Mantle‐Derived Fluids in the East Java Sedimentary Basin, Indonesia

“…The gas geochemistry survey described herein corroborates all the previously collected geophysical, petrographic, geochemical, and modeling evidences (Collignon et al, ; Fallahi et al, ; Malvoisin et al, ; Mazzini et al, ; Mazzini et al, ; Samankassou et al, ; Svensen et al, ). These converging data indicate that prior to the Lusi eruption and prior to the drilling of the BJP‐1 well, an overpressured zone in the deeply buried Ngimbang Fm.…”

“…Our new data also help to refine the fluids migration imaged by the ambient noise tomography acquired in the region that indicates the migration of hydrothermal fluids from the volcanic arc toward the sedimentary basin (Fallahi et al, ). The major migration pathway is linked to the WFS as well as W‐E‐oriented systems of antithetic fractures present around Lusi.…”

“…Results revealed that outgassing boiling fluids at the Lusi surface contain evidence of hydrothermal waters and a mix of inorganic and organic gases, including geothermal (thermo‐metamorphic and mantle‐derived) and biotic (i.e., thermogenic methane) gases (Mazzini et al, ; Mazzini et al, ). Ambient noise tomography revealed a connection between the Arjuno‐Welirang magma chamber and the Lusi conduit at around 4.5‐km depth, indicating the migration of magmatic and hydrothermal fluids toward the sedimentary basin (Fallahi et al, ). These results confirmed that Lusi is indeed not a mud volcano but rather a sediment‐hosted geothermal system (Mazzini & Etiope, ; Procesi et al, ).…”

Ambient-noise tomography of the Greater Geneva Basin in a geothermal exploration context

“…From a preliminary picking set, we observed that almost no data was retrievable below a period of 1 s. This 1 s period was thus used as a low-period picking boundary for the final picking set. A high-period picking boundary was also defined, aiming to have at least ∼1.5 wavelengths per inter-station distance (see for instance Mordret et al 2015;Obermann et al 2016;Fallahi et al 2017). Having no access to phase velocities, we estimated the wavelength based on the picked group-velocities, therefore slightly releasing the mentioned constraint to a probable range of 1-1.5 wavelengths per interstation distance.…”

Concentric Structures and Hydrothermal Venting in the Western Desert, Egypt

“…Currently, active sites are documented in the Guaymas Basin Rift Zone-Gulf of California (Pacific Ocean), in the Salton Sea geothermal field (California), within the Tiber Delta, at Fiumicino (central Italy), and in the Songliao Basin (northern China) (e.g., Helgeson, 1968;Welhan and Lupton, 1987;Mazzini et al, 2011;Berndt et al, 2016;Ciotoli et al, 2016;Shuai et al, 2018;Procesi et al, 2019). Today the largest active vent system is the Indonesian Lusi eruption (active since May 2006) that has been targeted by numerous multidisciplinary studies to fill the knowledge gap between modern and ancient hybrid systems (e.g., Mazzini et al, 2012;Fallahi et al, 2017;Lupi et al, 2018;Malvoisin et al, 2018;Mazzini, 2018;Miller and Mazzini, 2018).…”