Active deformation evidence in the offshore of western Calabria (southern Tyrrhenian Sea) from ultra-resolution multichannel seismic reflection data: results from the Gulf of Sant'Eufemia

An ultra-resolution, multichannel seismic reflection data set was collected during an oceanographic cruise organised in the frame of the “Earthquake Potential of Active Faults using offshore Geological and Morphological Indicators” (EPAF) project, which was founded by the Scientific and Technological Cooperation (Scientific Track 2017) between the Italian Ministry of Foreign Affairs and International Cooperation and the Ministry of Science, Technology and Space of the State of Israel. The data acquisition approach was based on innovative technologies for the offshore imaging of stratigraphy and structures along continental margins with a horizontal and vertical resolution at decimetric scale. In this work, we present the methodology used for the 2D HR-seismic reflection data acquisition and the preliminary interpretation of the data set. The 2D seismic data were acquired onboard the R/V Atlante by using an innovative data acquisition equipment composed by a dual-sources Sparker system and one HR 48-channel, slant streamers, with group spacing variable from 1 to 2 meters, at 10 kHz sampling rate. An innovative navigation system was used to perform all necessary computations to determining real-time positions of sources and receivers. The resolution of the seismic profiles obtained from this experiment is remarkable high respect to previously acquired seismic data for both scientific and industrial purposes. In addition to the seismic imaging, gravity core data were also collected for sedimentological analysis and to give a chronological constraint using radiocarbon datings to the shallower reflectors. The investigated area is located in the western offshore sector of the Calabrian Arc (southern Tyrrhenian Sea) where previous research works, based on multichannel seismic profiles coupled with Chirp profiles, have documented the presence of an active fault system. One of the identified faults was tentatively considered as the source of the Mw 7, 8 September 1905 seismic event that hit with highest macroseismic intensities the western part of central Calabria, and was followed by a tsunami that inundated the coastline between Capo Vaticano and the Angitola plain. On this basis, the earthquake was considered to have a source at sea, but so far, the location, geometry and kinematics of the causative fault are still poorly understood. In this study we provide preliminary results of the most technologically advanced ultra-high-resolution geophysical method used to reveal the 3D faulting pattern, the late Quaternary slip rate and the earthquake potential of the marine fault system located close to the densely populated west coast of Calabria

A Paleoseismic Record of Earthquakes for the Dead Sea Transform Fault between the First and Seventh Centuries C.E.: Nonperiodic Behavior of a Plate Boundary Fault

International audienceWe present new results from a paleoseismic trenching campaign at a site across the Jordan Gorge Fault (JGF), the primary strand of the Dead Sea Transform in northern Israel. In addition to the previously recognized earthquakes of 1202 and 1759 C.E., we observe evidence for eight surface-rupturing earthquakes prior to the second millennium C.E. The past millennium appears deficient in strain release with the occurrence of only two large ruptures, when compared with the preceding 1200 years. Assuming Gutenberg–Richter magnitude–frequency distribution, there is a discrepancy between measured rate of small-magnitude earthquakes (M < 4) from instrumental records and large earthquake rates from paleoseismic records. The in-terevent time of surface-rupturing earthquakes varies by a factor of two to four during the past 2 ka at our site, and the fault's behavior is not time predictable. The JGF may be capable of rupturing in conjunction with both of its southern and northern neighboring segments, and there is tentative evidence that earthquakes nucleating in the Jordan Valley (e.g., the 749 C.E. earthquake) could either rupture through the stepover between the faults or trigger a smaller event on the JGF. We offer a model of earthquake production for this segment in which the long-term slip rate remains constant while differing earthquake sizes can occur, depending on the segment from which they originated and the time since the last large event. The rate of earthquake occurrence in this model does not produce a time-predictable pattern over a period of 2 ka as a result of the interplay between fault segments to the south and north of the JGF. Online Material: High-resolution photomosaic logs of trench walls probability density function (PDF) and table of unit descriptions for channels 3 and 4

Offshore Evidence for an Undocumented Tsunami Event in the 'Low Risk' Gulf of Aqaba-Eilat, Northern Red Sea.

Although the Gulf of Aqaba-Eilat is located in the tectonically active northern Red Sea, it has been described as low-risk with regard to tsunami activity because there are no modern records of damaging tsunami events and only one tsunami (1068 AD) referred to in historical records. However, this assessment may be poorly informed given that the area was formed by and is located along the seismically active Dead Sea Fault, its population is known to fluctuate in size and literacy in part due to its harsh hyper-arid climate, and there is a dearth of field studies addressing the presence or absence of tsunamigenic deposits. Here we show evidence from two offshore cores for a major paleotsunami that occurred ~2300 years ago with a sedimentological footprint that far exceeds the scarce markers of the historically mentioned 1068 AD event. The interpretation is based on the presence of a laterally continuous and synchronous, anomalous sedimentological deposit that includes allochtonous inclusions and unique structural characteristics. Based on sedimentological parameters, these deposits could not be accounted for by other transport events, or other known background sedimentological processes

Comparison of North Beach sediment grain size distributions.

<p>Dotted black lines are measurements from recent flood sediments. Black dashed lines are modern North Beach seafloor sediments (1m and 3m water depth). Samples from the North Beach core include a set from the anomalous horizon (grey lines) and typical marine background (black lines).</p

Three-dimensional mesh models.

<p>a-d) 3D mesh models of bottom morphologies conducive to abnormal amplification and run-up scenarios [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145802#pone.0145802.ref050" target="_blank">50</a>] compared to GOA e)shaded and f and g) mesh model maps [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145802#pone.0145802.ref048" target="_blank">48</a>]. NB = North Beach, TY = Tur Yam.</p

Images of sediments.

<p>Photographs of the anomalous and non-anomolous samples from each core and comparative sample from modern collections that bears some resemblance to the anomalous horizon at each site. Upper photos represent typical background samples, which also resemble the modern surface; left: >63 micron sieved sample from 90-91cm North Beach core; right: >500 micron sieved sample from 240–241 cm in Tur Yam core. Middle photographs are examples from the anomalous sections of each core; left >63 micron sieved sample from 200–201 cm North Beach core; right >500 micron sieved sample from 110–113 cm in the Tur Yam core.</p

Worlwide tsunami records from past 3000 years.

<p>Comparison between number of tsunamis per century recorded [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145802#pone.0145802.ref004" target="_blank">4</a>], world population growth [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145802#pone.0145802.ref002" target="_blank">2</a>], and worldwide literacy rates beginning in 1950 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145802#pone.0145802.ref003" target="_blank">3</a>].</p

Sandy uppershelf sandy sediment core collection method.

<p>A) air hammer, B) weighted base c) preparing core for removal, d) core raised and en route to boat, e) airbag being retrieved prior to raising the sediment core which is attached below. Schematic of system (adapted from Goodman et al. 2009) Photo credits Eran Brokovich, B. Goodman, S. Breitstein.</p