Marine transform faults and associated fracture zones (MTFFZs) cover vast stretches of the ocean floor, where they play a key role in plate tectonics, accommodating the lateral movement of tectonic plates and allowing connections between ridges and trenches. Together with the continental counterparts of MTFFZs, these structures also pose a risk to human societies as they can generate high magnitude earthquakes and trigger tsunamis. Historical examples are the Sumatra-Wharton Basin Earthquake in 2012 (M8.6) and the Atlantic Gloria Fault Earthquake in 1941 (M8.4). Earthquakes at MTFFZs furthermore open and sustain pathways for fluid flow triggering reactions with the host rocks that may permanently change the rheological properties of the oceanic lithosphere. In fact, they may act as conduits mediating vertical fluid flow and leading to elemental exchanges between Earth’s mantle and overlying sediments. Chemicals transported upwards in MTFFZs include energy substrates, such as H2 and volatile hydrocarbons, which then sustain chemosythetic, microbial ecosystems at and below the seafloor. Moreover, up- or downwelling of fluids within the complex system of fractures and seismogenic faults along MTFFZs could modify earthquake cycles and/or serve as “detectors” for changes in the stress state during interseismic phases. Despite their likely global importance, the large areas where transform faults and fracture zones occur are still underexplored, as are the coupling mechanisms between seismic activity, fluid flow, and life. This manuscript provides an interdisciplinary review and synthesis of scientific progress at or related to MTFFZs and specifies approaches and strategies to deepen the understanding of processes that trigger, maintain, and control fluid flow at MTFFZs.
Abstract Offshore and onshore stratigraphic studies, together with high-resolution shallow seismic reflection profiling and multibeam bathymetric mapping, were carried out in the western and central part of the Izmit Gulf. These studies indicate that the Izmit Gulf was a lacustrine environment as part of the Marmara ‘Lake’ during the late glaciation and early deglaciation until ∼12 kyr BP, when the Marmara Basin was inundated by the Mediterranean waters. Correlation of 14 C-dated onshore and offshore stratigraphic units in the Western Izmit Gulf indicates that generally coarse late glacial sediments overlie a marked erosional surface formed during the low water level of the Marmara ‘Lake’. These coarse sediments are succeeded by 10.4–7 kyr BP old transgressive, and by late Holocene post-transgression mud units. The bathymetry and sub-bottom Chirp profiles clearly show that the paleoshoreline of the Gulf was located at −85 m, having been controlled by the bedrock sill depth of the Canakkale Strait. Another paleoshoreline observed at −65 m on the northern margin of the Western Izmit and Karamursel basins was probably formed during the Younger Dryas sea-level stillstand. The shelf areas during this time were colonized by bioherms, which were subsequently drowned and disappeared after a further rise of the sea level. The presence of a −65 m marine paleoshoreline in the Karamursel Basin indicates that the sill restricting this basin to the west was much deeper than its present −55 m level and was located further south. The Golcuk Basin, restricted by a −38 m sill to its west, was probably not flooded by marine waters until ∼9 kyr BP.
Abstract Cheko, a small lake located in Siberia close to the epicentre of the 1908 Tunguska explosion, might fill a crater left by the impact of a fragment of a Cosmic Body. Sediment cores from the lake’s bottom were studied to support or reject this hypothesis. A 175‐cm long core, collected near the center of the lake, consists of an upper ∼1 m thick sequence of lacustrine deposits overlaying coarser chaotic material. 210 Pb and 137 Cs indicate that the transition from lower to upper sequence occurred close to the time of the Tunguska Event. Pollen analysis reveals that remains of aquatic plants are abundant in the top post‐1908 sequence, but are absent in the lower pre‐1908 portion of the core. These results, including organic C, N and δ 13 C data, suggest that Lake Cheko formed at the time of the Tunguska Event.
Abstract. The Ionian Sea in southern Italy is at the center of active interaction and convergence between the Eurasian and African-Adriatic plates in the Mediterranean. This area is seismically active with instrumentally/historically-recorded Mw > 7.0 earthquakes and it is affected by recently-discovered long strike-slip faults across the active Calabrian accretionary wedge. Many mud volcanoes occur on top of the wedge. A recently-discovered one (here named Bortoluzzi Mud Volcano, BMV) was surveyed during the Seismofaults 2017 cruise (May 2017). Bathymetric-backscatter surveys, seismic reflection profiles, geochemical and earthquake data as well as a gravity core are here used to geologically, geochemically, and geophysically characterize this structure. The BMV is a circular feature ≃22 m high and ≃1100 m in diameter with steep slopes (up to a dip of 22°). It sits atop the Calabrian accretionary wedge and a system of flower-like oblique-slip faults that are probably seismically active as demonstrated by earthquake hypocentral and focal data. Geochemistry of water samples from the seawater column on top of the BMV shows a significant contamination of the bottom waters from saline (evaporite-type) CH4-dominated crustal-derived fluids similar to the fluids collected from a mud volcano located in the Calabria main land over the same accretionary wedge. These results attest for the occurrence of an open crustal conduit through the BMV down to at least the Messinian evaporites at about −3000 m. This evidence is also substantiated by Helium isotope ratios and by different geochemical data from three sea water columns located elsewhere in the Ionian Sea. Conclusions are drawn on the origin of the BMV and on the potential of this type of structures for tracking the seismic cycle of active faults. Due to the widespread diffusion of mud volcanoes in seismically active settings, this study may contribute to indicate a potential and feasible future path for the use of these ubiquitous structures in favor of the mitigation of natural hazards.
An open problem concerning the Mw 7.4, 1999 İzmit earthquake along the North Anatolian Fault (NAF) system is the apparent conflict between estimates of strike‐slip deformation based on field and remote sensing data. This is due to the fact that the main strand of the NAF west of the epicenter lies below the Sea of Marmara. Seismological evidence and models based on synthetic aperture radar interferometry suggest that coseismic and early postseismic displacement accumulated after the earthquake could have reached the western end of the İzmit Gulf and possibly the southern edge of the Çınarcık Basin, tapering off along the northern coast of the Armutlu Peninsula, more than 60 km from the epicenter. This scenario is not confirmed by onshore field observations that point toward a termination of the surface rupture around 30 km to the east. These discrepancies convey high uncertainties in the estimate of the tectonic load produced by the İzmit earthquake on the adjacent fault segment toward Istanbul. We analyzed data from different sources, including high‐resolution marine geophysical surveys and two Nautile dives along the fault‐controlled canyon that connects İzmit Çınarcık basins. Our observations suggest that the surface rupture of the 1999 İzmit earthquake propagated through the shallow Gulf but did not reach the deep Marmara basins. In fact, along the slope between Çınarcık and the western end of the İzmit Gulf, we do not observe fault‐related ruptures affecting the seafloor but rather a series of active gas seeps and “black patches” that mark the presence of known active faults. Our findings have implications for seismic risk assessment in the highly populated region of Istanbul, both for the estimate of tectonic load transferred to the next fault segments and the location of the next earthquake.
