Possible sources of hydrothermal activity and mud volcanism in southern Sakhalin inferred from local earthquake seismic tomography

Abstract

We present the first seismic model of the crust beneath Sakhalin based on P and S‐wave arrival time data from local earthquakes. Based on the results of numerous synthetic tests, we conclude that this model has fair horizontal and vertical resolution to 20–25 km depth. At shallow depths, seismic anomalies are clearly associated with known geological structures, such as the high‐velocity Paleozoic Susunai block and the low‐velocity Cenozoic fold belts along the West Sakhalin Mountains. In vertical sections, we observe westward underthrusting of the Susunai block to a distance of at least 70 km, which may represent the regional compression and considerable crustal shortening in this area. Based on the tomography results, we hypothesize about the origin of the mud volcanism in southern Sakhalin. We propose that because of the general westward underthrusting regime in Sakhalin, hydrocarbon‐rich shelf sediments may be entrained to considerable depths under the rigid Susunai block, which serves as a nonpermeable cover. The released gases find the weakest zones around the Susunai block and along the Tym‐Poronay Fault and escape to the surface to form the South Sakhalin and Lesnovsky mud volcano fields.

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

“…Seismic tomography is a powerful tool to explore the velocity structure of the upper lithosphere (Nolet, 1987;Tromp et al, 2005). Using this technique along with dense seismic networks, it is possible to identify highand low-velocity zones associated with geological phenomena and structures such as hydrothermal systems (Obermann et al, 2016), magmatic bodies (Koulakov et al, 2009;Koulakov & Shapiro, 2015), mud volcanoes (Koulakov et al, 2017), and ore deposits (Olivier et al, 2015). Piercement structures (such as Lusi) are geological phenomena driven also by the development of elevated pore pressure and fluid migration at depth.…”

Ge-Hg-Rich Sphalerite and Pb, Sb, As, Hg, and Ag Sulfide Assemblages in Mud Volcanoes of Sakhalin Island, Russia: An Insight into Possible Origin

“…The graben, interpreted as a Jurassic subduction zone, is filled with 2 to 8 km of unconsolidated Cenozoic sediments and is bounded by the West-Sakhalin and Tym-Poronay fault systems, which generated many large earthquakes in the Sea of Japan and in Sakhalin Island. The regional Tym-Poronay and East Sakhalin faults stretch all along Sakhalin Island and extend into Hokkaido Island as the Hidaku belt [19][20][21].…”

“…One such block in the southern part of Sakhalin within the East Sakhalin uplift represents the basement uplifted during a collision with the Kurile forearc (Susunai metamorphic complex). [26]; 4 = faults, after [20], abbreviated as: ESF = East Sakhalin Fault, HB = Hidaku Belt, TPF = Tym-Poronay Fault, WSF = West Sakhalin Fault. 5 = sampled (a) and unsampled (b) mud volcanoes; 6 = aureoles of atmochemical mercury dispersion, after [27].…”

“…Mineragenic zone after [28]: 7 = the belt of Sb-Hg mineralization; 8 = Neogenic Ge-rich coal. 9 = hot springs and boreholes, after [20].…”

“…The recent geodynamics of the area has been controlled by its location at the convergent boundaries of the Eurasian, Okhotsk, North American, and Pacific Plates. Being a part of the Sakhalin-Hokkaido orogenic belt, the island, along with the Kamchatka Peninsula, is among the most active seismic regions of Russia [17][18][19][20]. The Sakhalin mud volcanism is an effect of the high regional seismicity.…”