Description: ALKOR cruise AL600 served as a marine geophysical field course for ‘Physics of the Earth System’ bachelor students at Kiel University. Beside taking an active role in planning and realization of the individual geophysical measurements, the students also performed some first processing and interpretation of the obtained data. This work had to be documented in form of a scientific presentation as well as writing of the respective chapter in this cruise report. For the following chapters, we (Sebastian Krastel, Jens Schneider von Deimling) decided to only slightly modify the text and figures provided by the students. This should emphasize the student’s achievements, and underline the overarching aim of the cruise to train the students in acquisition, processing, and documentation of marine geophysical data.

Description: Highlights • the western Ionian Basin shows three distinct canyon-channel systems. • 〉140 m-thick gravity flow along main passageway in the east; velocity 5–6 m s−2. • numerous erosional and depositional bedforms (e.g., scours, sediment waves). • north-eastern Sicily and southern Calabria are potential source areas. • main failure likely offshore between San Leo and Bocale (southern Calabria). Abstract Earthquakes, tsunamis and gravity flows are common processes offshore Eastern Sicily and pose a significant hazard to coastal communities and infrastructure. The 1908 Messina earthquake and tsunami resulted in 〉60,000 casualties. It caused a large turbidity current, which broke the Malta-Zante telegraph cable. Yet, this gravity flow remains poorly characterised in terms of its route and flow behaviour. A comprehensive analysis of multibeam echosounder data, sub-bottom profiles, and sediment cores has been carried out to improve our understanding about gravity flow activity within conduit systems of the western Ionian Basin to reconstruct the characteristics of the 1908 sediment flow (e.g., erosion, velocity, source region). Three main canyon-channel systems can be distinguished within the study area. The easternmost system (C3) appears to be the most active in terms of sediment transport. There are numerous erosional and depositional bedforms, including large-scale scours (〉100 m-long), turbidite sediment waves and channel wall collapses that are not overprinted by younger events. The other two canyon-channel systems (C1, C2) do not show many bedforms indicative of repeated and recent gravity flow activity. Indeed, the transport of the majority of sediment discharged into the western system (C1) is limited to 〈25 km downslope from the continental slope, while the central system (C2) facilitates sediment deposition from gravity flows. C3 is, thus, suggested to have been the main passageway of the 1908 sediment flow. It also leads directly to two of three cable break locations. The most likely source areas for the gravity flow are north-eastern Sicily and southern Calabria. Bedforms indicate a flow thickness of 〉170 m along the upper channel portion of C3 and 〉 140 m along its lower portion close to the cable breaks. An average flow velocity of 5.6 to 6.3 ms−1 is reconstructed, given the timing of the breaks and length of the canyon-channel system. The flow may have locally decelerated and accelerated while bypassing morphologic highs and knickpoints. These new findings significantly improve our understanding of the 1908 gravity flow (e.g., passageways, depositional/erosional behaviour, thickness, velocity) and provide important insights into gravity flow events in general, especially those with a large run-out. This knowledge is needed to assess potential hazards associated with these events.

Description: Highlights • A fiber optic strain cable is used to monitor a fault offshore Catania, Sicily. • Brillouin laser reflectometry detects 2.5 cm of cable elongation on the seafloor. • The cable elongation may be caused by fault slip or by seabottom currents. • Submarine telecom cables are likely suitable to detect deformation on the seafloor. Abstract Oceans cover more than 70 percent of the Earth's surface making it difficult and costly to deploy modern seismological instruments here. The rapidly expanding global network of submarine telecom cables offers tremendous possibilities for seismological monitoring using laser light. Recent pioneer studies have demonstrated earthquake detection using lasers in onland and submarine fiber optic cables. However, permanent strain at the seafloor has never before been measured directly as it happens. With this aim, we deployed a dedicated 6-km-long fiber optic strain cable, offshore Catania Sicily, in 2000 m water depth, and connected it to a 29-km long electro-optical cable for science use. We report here that deformation of the cable equivalent to a total elongation of 2.5 cm was observed over a 21-month period (from Oct. 2020 to Jul. 2022). Brillouin laser reflectometry observations over the first 10 months indicate significant strain (+25 to +40 microstrain) at two locations where the cable crosses an active strike-slip fault on the seafloor, with most of the change occurring between 19 and 21 Nov. 2020. The cause of the strain could be fault slip or seabottom currents. During the following 11 months, the strain amplitude increased to +45 to +55 microstrain, affecting a longer portion of the cable up to 500 m to either side of the first fault crossing. A sandbag experiment performed on the distal portion of the cable (3.2–6.0 km) starting Sept. 2021 demonstrates how the fiber optic cable deforms in response to an applied load and how the deformation signal partially dissipates over time due to the elastic properties of the cable. These preliminary results are highly encouraging for the use of BOTDR (Brillouin Optical Time Domain Reflectometry) laser reflectometry as a technique to detect strain at the seafloor in near real time and to monitor the structural health of submarine cables.

Description: Research cruise AL579 is part of the bachelor course "Physics of the Earth System - Geophysics, Meteorology and Oceanography" at the University of Kiel. It is the field exercise for marine geophysics and hydroacoustics. The aim of the annually recurring cruise is to give students a practical insight into the acquisition, processing, documentation, and interpretation of marine geophysical data. AL579 took place from August 20th -28th 2022 with the main study areas in Eckernförde Bay and the Bay of Mecklenburg. Parts of the scientific crew changed during a stopover in Kiel on Wednesday, 24.8.2022. In Eckernförde Bay we mainly collected Multibeam Echosounder (MBES) and INNOMAR Subbottom Echosounder (SES) data calibrated by CTD measurements close to the pockmark field off Mittelgrund. On Wednesday, 24.8.2022 we tested a new Ocean Bottom Seismometer (OBS) prototype. In the Bay of Mecklenburg, the focus was on Blinkerhügel and the seafloor structures further west where an enigmatic stone structure was discovered in 2021. This area was surveyed with Sidescan Sonar, MBES, SES, and CTD measurements and several video transects with an underwater drone. We also collected two sets of multi-channel seismic data to investigate the deeper structures of the Western Baltic Sea and the Bay of Mecklenburg.

Description: Submarine geomorphology, the study of landforms and processes within the submarine domain, is a young discipline that owes its birth to technological achievements that made it possible to explore the underwater sphere of our Earth system. Submarine domains represent over 70% of Earth's surface, i.e. the largest geomorphic system on our planet (more than twice the size of what we can observe on Earth's land surface). From the middle of the last century onwards, technological advances have led to more and more high-performance acoustic equipment and robotic underwater systems, enabling us to depict and investigate, in ever greater detail, parts of the ocean floor long thought to be unfathomable. The present chapter gives an overview of the extent to which technological progress has strongly determined the way in which the study of landscapes and landforms within the submarine domain is approached, creating substantial differences to approaches used in classical studies of geomorphology. Main drivers of seafloor geomorphic changes are introduced to provide a representative summary of the variety of landforms generated by the action of a range of tectonic, sedimentary, and bio-geochemical processes, including the impact of human activity. The chapter concludes with a brief discussion on the relevance of the applied value of submarine geomorphological research, its new trends, and the key contribution it is providing to confirming the importance of geomorphology to the full range of Earth system sciences and environment-related topics.

Description: Argnani (2021, hereinafter ARG2021) commented on the paper by Barreca et al. (2021, hereinafter BRC2021) titled: “The Strait of Messina: Seismotectonics and the source of the 1908 earthquake”, in which a new seismotectonic model and constraints on the possible source fault (the so-called W-Fault) for the 1908 disastrous seismic event were provided. Results from BRC2021 led to a revision of most of the previously published papers on the issue. ARG2021 commented both on the recent activity of the W-Fault and even about its existence in the offshore. In fact, according to the author's inferences: “it may belong to a fault system that is no longer active” and, contradictorily, “the offshore occurrence of the W-Fault is not supported by the data”. The comment is mostly based on a new tectonic interpretation that the author performed directly on the BRC2021 figures, where the offshore portion of the W-fault is illustrated. In this reply, we demonstrate that the interpretation provided by ARG2021 is affected by several oversights that led the author to erroneous conclusions about the issue. Accordingly, we strongly confirm both the occurrence of the W-Fault in the offshore and the present-day activity of this structure, the only active fault capable of producing large earthquakes in the Strait of Messina area.

Description: Published

Description: 103962

Description: 3T. Fisica dei terremoti e Sorgente Sismica

Description: JCR Journal

Description: Argnani (2021) provides a commentary (hereafter ARGN) on our paper titled: “Deformation Pattern of the Northern Sector of the Malta Escarpment: Fault Dimension, Slip Prediction, and Seismotectonic Implications,” which was published in the journal Frontiers in Earth Science in January 2021 (Gambino et al., 2021, hereafter GAMB). Through the interpretation of eight new seismic profiles (six of which are reported in Supplementary Figure S1 of GAMB) crossing the Malta Escarpment, GAMB pointed to a better definition of the geometry of three active faults (F1, F2, F3) and their seismic potential by employing slip tendency modeling and forward analysis. The results suggest that F3 is prone to be reactivated under the achieved stress field and has the capacity of generating M 〉 7 earthquakes. ARGN raises concerns about the higher resolution and less penetration of the eight newly acquired high-resolution multichannel reflection seismic profiles and the seismic-stratigraphic pattern proposed by GAMB. According to ARGN, “the seismic profiles analyzed by GAMB belong to different sets and have very different seismic characters and resolution, making seismic facies correlation pretty difficult, also because no tie lines are available. As a result, stratigraphic correlations are highly speculative and the ensuing uncertainties undermine the timing of the tectonic evolution envisaged by GAMB, as well as the age and rate of activity of tectonic structures.” Furthermore, ARGN argues on the hypothesis of an early large-scale slope instability affecting the area. Most of the statements of ARGN seem to be based on his available older multichannel reflection seismic profiles, which have, indeed, a higher penetration but less resolution. We also agree that high-resolution digital multichannel seismic profiles are not easily comparable with low-resolution multichannel seismic lines, but we see the clear advantage of a state-of-the-art technology to image the upper strata of sedimentary systems. The used system proved its robustness in many different settings worldwide and has been successfully used for many pre-site surveys for drilling campaigns for the IODP and ICDP. As a result, we rebut point-by-point ARGN’s comments and stand by our model on the active deformation pattern and seismotectonics of the northern sector of the Malta Escarpment.

Description: Published

Description: 886439

Description: 2T. Deformazione crostale attiva

Description: JCR Journal