3D Local Earthquake Tomography of the Ecuadorian Margin in the Source Area of the 2016 Mw 7.8 Pedernales Earthquake

Based on manually analyzed waveforms recorded by the permanent Ecuadorian network and our large aftershock deployment installed after the Pedernales earthquake, we derive three-dimensional Vp and Vp/Vs structures and earthquake locations for central coastal Ecuador using local earthquake tomography. Images highlight the features in the subducting and overriding plates down to 35 km depth. Vp anomalies (∼4.5–7.5 km/s) show the roughness of the incoming oceanic crust (OC). Vp/Vs varies from ∼1.75 to ∼1.94, averaging a value of 1.82 consistent with terranes of oceanic nature. We identify a low Vp (∼5.5 km/s) region extending along strike, in the marine forearc. To the North, we relate this low Vp and Vp/Vs (1.85) which we interpret as deeply fractured, probably hydrated OC caused by the CR being subducted. These features play an important role in controlling the seismic behavior of the margin. While subducted seamounts might contribute to the nucleation of intermediate megathrust earthquakes in the northern segment, the CR seems to be the main feature controlling the seismicity in the region by promoting creeping and slow slip events offshore that can be linked to the updip limit of large megathrust earthquakes in the northern segment and the absence of them in the southern region over the instrumental period

Hunt for Palytoxins in a Wide Variety of Marine Organisms Harvested in 2010 on the French Mediterranean Coast

During the summer of 2010, 31 species including fish, echinoderms, gastropods, crustaceans, cephalopods and sponges were sampled in the Bay of Villefranche on the French Mediterranean coast and screened for the presence of PLTX-group toxins using the haemolytic assay. Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used for confirmatory purposes and to determine the toxin profile. The mean toxin concentration in the whole flesh of all sampled marine organisms, determined using the lower- (LB) and upper-bound (UB) approach was 4.3 and 5.1 µg·kg−1, respectively, with less than 1% of the results exceeding the European Food Safety Authority (EFSA) threshold of 30 µg·kg−1and the highest values being reported for sea urchins (107.6 and 108.0 µg·kg−1). Toxins accumulated almost exclusively in the digestive tube of the tested species, with the exception of octopus, in which there were detectable toxin amounts in the remaining tissues (RT). The mean toxin concentration in the RT of the sampled organisms (fishes, echinoderms and cephalopods) was 0.7 and 1.7 µg·kg−1 (LB and UB, respectively), with a maximum value of 19.9 µg·kg−1 for octopus RT. The herbivorous and omnivorous organisms were the most contaminated species, indicating that diet influences the contamination process, and the LC-MS/MS revealed that ovatoxin-a was the only toxin detected

Tests de capteurs OBS

International audienceL'action spécifique Sismologie Marine Mobile (SMM) a été créée au sein de Résif. Les 3 parcs OBS français se sont fédérés pour offrir une instrumentation marine de pointe pouvant répondre aux besoins des chercheurs. Le projet d'investissement d'avenir Marmor, financé par l'ANR (PIA3-ESR-Equipex+), permet l'achat et la jouvence d'instruments de ce parc. Le choix des capteurs qui équiperont les OBS acquis est devenu prééminente. Un groupe de travail formé d'ingénieurs et de chercheurs a été créé afin d'éclairer ce choix devant l'absence de données comparatives

Diversity of bacteria associated with the cold water corals Lophelia pertusa and Madrepora oculata

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Tests de capteurs OBS

International audienceL'action spécifique Sismologie Marine Mobile (SMM) a été créée au sein de Résif. Les 3 parcs OBS français se sont fédérés pour offrir une instrumentation marine de pointe pouvant répondre aux besoins des chercheurs. Le projet d'investissement d'avenir Marmor, financé par l'ANR (PIA3-ESR-Equipex+), permet l'achat et la jouvence d'instruments de ce parc. Le choix des capteurs qui équiperont les OBS acquis est devenu prééminente. Un groupe de travail formé d'ingénieurs et de chercheurs a été créé afin d'éclairer ce choix devant l'absence de données comparatives

Tests de capteurs OBS

International audienceL'action spécifique Sismologie Marine Mobile (SMM) a été créée au sein de Résif. Les 3 parcs OBS français se sont fédérés pour offrir une instrumentation marine de pointe pouvant répondre aux besoins des chercheurs. Le projet d'investissement d'avenir Marmor, financé par l'ANR (PIA3-ESR-Equipex+), permet l'achat et la jouvence d'instruments de ce parc. Le choix des capteurs qui équiperont les OBS acquis est devenu prééminente. Un groupe de travail formé d'ingénieurs et de chercheurs a été créé afin d'éclairer ce choix devant l'absence de données comparatives

Seismic profiles across the North Anatolian Fault in the Aegean Sea

International audienceThe North Anatolian Fault (NAF) is a >1200 km-long continental strike-slip fault system, acting as the plate boundary between Eurasia and Anatolia. West of the Yeniçaga fork in Turkey, the NAF divides in two main strands: the Main Marmara Fault crossing the Marmara Sea to the North, and a southern branch of the NAF crossing the Biga Peninsula. Both strands end in the Aegean Sea, connecting conspicuous horsetail terminations offshore eastern Greece at the North Aegean Trough and off Skyros Island. The northern Aegean Sea is therefore a key area to understand the structural evolution of the North Anatolian strike-slip fault system since its formation in the Late Miocene. Stratigraphic markers in the Aegean Sea provide optimal conditions for the study of the fault system evolution at the time scale of 105-106 years. Here we present a new set of shallow seismic reflection data crossing the NAF in the northern Aegean Sea, acquired in July 2017 onboard the R/V Tethys II (INSUCNRS/IFREMER). The penetration of the seismic signal reaches the Messinian unconformity. This new datasetallows us to investigate the sub-surface structure of the fault system and to identify key unconformities related to the formation of the horsetail terminations in the Late Pliocene-Early Pleistocene. These new elements will help to better understand the structural evolution of the NAF in the framework of back arc extension in the Aegean Sea since the Late Miocene

Seismic imaging across a slow slip event area, along the Ecuadorian subduction zone

International audienceThe Mw 8.8 1906 earthquake that occurred at the Ecuador-Colombia subduction zone is the 7th largest event ever recorded worldwide, and one of several large earthquakes that have affected the region since then.At its southern border, episodes of aseismic slip have been recorded at the shallow updip part of the subduction interplate fault, in the form of both slow slip events (Vaca et al., 2018) and afterslip in the aftermath of the 2016 Mw 7.8 Pedernales earthquake (Rolandone et al., 2018). During the geophysical experiment HIPER, in march 2020, 47 Ocean Bottom Seismometers (OBS) have been densely deployed along a 93-km-long trench-normal profile, crossing the supposed area of the SSE event below the margin. These OBSs recorded the shots produced by 4990 cu.in. airguns, with the R/V Atalante, in order to obtain a high-resolution P-velocity 2D profile. A coincident Multi-Channel Seismic (MCS) profile was acquired, providing information on the structure of the oceanic crust (see companion abstract by Schenini et al.). The combined inversion of the first-arrival and oceanic Moho reflection PmP phases, using the traveltime tomography Tomo2D code (Korenaga et al., 2000), provides both the P-velocity structure of the subducting and upper plates as well as the oceanic Moho geometry down to 20 km depth. The obtained velocity model displays a low-velocity anomaly within the Nazca plate’s oceanic crust at the trench together with a strong increase of the oceanic crust thickness over a distance of only 50 km (from 5.5 km to 16 km thick). The thickened crust in our profile shares a clear seismic signature affinity with the nearby aseismic Carnegie Ridge, resulting from the interaction between the Galapagos hotspot and the Cocos-Nazca Spreading Center (CNSC), 20 Myr ago. Taking this into account, our results nevertheless show a low-velocity anomaly of 11% at the trench which is higher than Vp anomalies observed before the trench in other subduction zones, that have been related to oceanic crust hydration, favored by bending faults. This may thus be an indication of excessive fracturing and hydration of this thicker oceanic crust portion of the Carnegie aseismic ridge.Next steps will be to better understand the influence of this feature on the slipping behavior, by observing the coincident and adjacent MCS profiles

Travel-time tomography imaging the Ecuadorian subduction, north of the Mw 7.8 Pedernales earthquake

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