Is the machecoul fault the source of the ∼M6 1799 Vendée earthquake (France)?

Summary The ∼M6 1799 Bouin earthquake is considered as one of the largest earthquakes to have struck Western France. However, the seismogenic source potentially responsible for this event remain marginally documented. We present results from a focused offshore-onshore multidisciplinary survey in its meizoseismal area in order to identify the fault segments that potentially ruptured during this earthquake. Based on macroseismic data and the geology, we focused our study on the so-called Machecoul Fault as a potential source of the 1799 Bouin event. Our survey includes extensive high-resolution seismic reflection, high resolution bathymetry and a one-year seismological survey. These data were combined with existing topography, onshore gravity data and drill data to document the geometry of the Marais Breton / Baie de Bourgneuf basin, the past tectonic activity and the current local microearthquakes at depth along its bounding faults. Offshore and onshore observations suggest a recent activity of the segmented Machecoul Fault bounding the basin to the North. Offshore, the planar contact between the Plio-Quaternary sediments and the basement along the fault trace as well as the thickening of these sedimentary units near this contact suggests tectonic control rather than erosion. Onshore, the recent incision of the footwall of the fault suggests a recent tectonic activity. The temporary local seismological experiment deployed between 2016 and 2017 recorded a diffuse micro-seismicity down to the depth of 22 +/-5 km along the southward dipping Machecoul Fault, associated with predominantly normal fault mechanisms. Altogether, these results suggest that the Machecoul Fault is a serious candidate for being the source of the historical Bouin 1799 earthquake.

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Μorphometric Analysis for the Assessment of Relative Tectonic Activity in Evia Island, Greece

Geosciences ◽

10.3390/geosciences10070264 ◽

2020 ◽

Vol 10 (7) ◽

pp. 264

Author(s):

Kanella Valkanou ◽

Efthimios Karymbalis ◽

Dimitris Papanastassiou ◽

Mauro Soldati ◽

Christos Chalkias ◽

...

Keyword(s):

Spatial Distribution ◽

Fault Zone ◽

Normal Fault ◽

Morphometric Parameters ◽

Tectonic Activity ◽

Asymmetry Factor ◽

Drainage Basins ◽

Fault Systems ◽

The North ◽

Integrated Index

The aim of this study is to evaluate the relative tectonic activity in the north part of the Evia Island, located in Central Greece, and to investigate the contribution of neotectonic processes in the development of the fluvial landscape. Five morphometric parameters, including Drainage Basin Slope (Sb), Hypsometric Integral (Hi), Asymmetry Factor (Af), Relief Ratio (Rh), and Melton’s Ruggedness Number (M), were estimated for a total of 189 drainage basins. The catchments were classified into two groups, according to the estimated values of each morphometric parameter, and maps showing their spatial distribution were produced. The combination of the calculated morphometric parameters led to a new single integrated Index of relative tectonic activity (named Irta). Following this indexing, the basins were characterized as of low, moderate, or high relative tectonic activity. The quantitative analysis showed that the development of the present drainage systems and the geometry of the basins of the study area have been influenced by the tectonic uplift caused by the activity of two NW-SE trending offshore active normal fault systems: the north Gulf of Evia fault zone (Kandili-Telethrion) and the Aegean Sea fault zone (Dirfis), respectively. The spatial distribution of the values of the new integrated index Irta showed significant differences among the drainage basins that reflect differences in relative tectonic activity related to their location with regard to the normal fault systems of the study area.

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SEABED TOPOGRAPHY MAPPING IN SANGIHE TALAUD WATERS USING MULTIBEAM ECHOSOUNDER

Oseanika ◽

10.29122/oseanika.v1i1.4054 ◽

2020 ◽

Vol 1 (1) ◽

Author(s):

Dwi Haryanto ◽

Muhamad Irfan ◽

Taufan Wiguna ◽

Hendra Kurnia Febriawan

Keyword(s):

High Resolution ◽

Multibeam Echosounder ◽

The North ◽

North Sulawesi ◽

Marine Habitats ◽

Seabed Topography ◽

High Resolution Bathymetry ◽

New Discovery

The application of multibeam echosounder for seabed topography has been developing rapidly. Multibeam echosounder is a very efficient way to get a wide seabed topography coverage for each ping, so it can produce high-resolution seabed topography maps. These maps can be used as a reference for further investigation or exploration, for example geological studies, marine habitats and others. RV Baruna Jaya IV is operated by Laboratory for Marine Survey Technology â€“ BPPT that have been hull mounted equipped a Germany technology multibeam echosunder Seabeam 1050D system. The Seabeam 1050D allow to sweep measuring the seabed topography using 126 beams simultaneously from port to starboard sites. R.V. Baruna Jaya IV and the Okeanos Explorer of NOAA have been conducted joint Indonesia - U.S. Expedition to Sangihe Talaud waters (INDEX SATAL) in the north area of the North Sulawesi Province during July - August, 2010. Seabed topography of less than 2000 metres were recorded by Seabeam 1050D system, the area of larger depths of 2000 metres to 6000 metres recorded by Simrad EM-302 from Okeanos Explorer. The seabed topography in Sangihe Talaud waters has a varied seabed topography. The new discovery that showed on the map is a 1600 m height of seamount, risen up from the depth of 2300m to 710m. Others geological seabed can be identified according to high resolution bathymetry map resulted from this study.Keywords: multibeam echosounder, seabed topography, seamount, Sangihe Talaud

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Gravity anomaly to identify Walanae fault using second vertical derivative method

Journal of Physics Theories and Applications ◽

10.20961/jphystheor-appl.v2i1.29008 ◽

2018 ◽

Vol 2 (1) ◽

pp. 34

Author(s):

Marsellei Justia ◽

Muhammad Fikri H Hiola ◽

Nur Baiti Febryana S

Keyword(s):

Gravity Data ◽

Moving Average ◽

Normal Fault ◽

Reverse Fault ◽

The South ◽

Vertical Derivative ◽

The North ◽

Free Air ◽

Free Air Anomaly ◽

Fault Mechanism

Research has been conducted to identify the Walanae Fault, coordinates 4–6 S and 118-120 E using anomalous gravity data. This research uses data measurement of Topography and the Free Air Anomaly from the TOPEX/Poseidon satellite. Then the authors processed to obtain the bouguer anomalies and made modeling by using the Surfer 10. The authors used the Second Vertical Derivative (SVD) with filter Elkins of Moving Average then analyze the graph of the SVD. The results shows the value of the residual anomaly in the north of fault is 25.21 mGal, in the middle occur range 17.67 mGal to 24.98 mGal and 30,376 mGal in the south of fault. The authors indicates the existence of a difference between the gravity between the Walanae Fault with surrounding geologic. From these results also show that Walanae Fault has a reverse fault mechanism in the northern part and the normal fault mechanism in the middle to the south, the authors conclude that the Walanae Fault is divided into two segments, that is the northern and the southern segment.

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Earthquake Hazards of the Grand Teton National Park Emphasizing the Teton Fault

The UW National Parks Service Research Station Annual Reports ◽

10.13001/uwnpsrc.1987.2649 ◽

1987 ◽

Vol 11 ◽

pp. 106-130

Author(s):

D. Susong ◽

R. Smith ◽

R. Bruhn

Keyword(s):

Fault Zone ◽

Gravity Data ◽

Hanging Wall ◽

Regional Scale ◽

Normal Fault ◽

Earthquake Hazards ◽

Eastern Front ◽

The North ◽

Teton Range ◽

Structural Boundary

The Teton normal-fault zone extends for over 80 km along the eastern front of the Teton Range. Mapping and profiling of Quaternary fault scarps shows that the scarps are nearly continous for 55 km with scarp heights varying from about 10 m to 40 m. The largest scarps occur adjacent to the topographically highest parts of the Teton range. The scarps locally offset glacial moraine crests in a left-lateral sense. On a regional scale the scarps exhibit a right-stepping, en echelon geometry that is also consistent with a component of left-lateral displacenent. The Teton fault is structurally subdivided into three segments. One prominent geometrical segment boundary occurs just south Taggart Lake, where the range front bends through an angle of 23Â° and a major structural boundary extends through the hanging wall basin, as inferred by gravity data. This boundary may have influenced the history of Quaternary earthquake occurrences because vertical offset across faults scarps is greater to the north of the boundary, than to the south. The lengths of the proposed segments and scarp size are consistent with M7 to 7.5 earthquakes for the Teton fault zone.

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STRONG EARTHQUAKES in the NORTH of the LAKE BAIKAL REGION (Mw=4.6–4.7) in 2015

Zemletriaseniia Severnoi Evrazii [Earthquakes in Northern Eurasia] ◽

10.35540/1818-6254.2021.24.27 ◽

2021 ◽

pp. 276-290

Author(s):

Ya. Radziminovich ◽

V. Melnikova ◽

N. Gileva ◽

A. Filippova

Keyword(s):

Lake Baikal ◽

Baikal Region ◽

Moment Tensor ◽

Seismic Hazard Assessment ◽

Normal Fault ◽

Seismic Moment Tensor ◽

Macroseismic Data ◽

Strong Earthquakes ◽

The North ◽

Lake Baikal Region

The paper considers three relatively strong earthquakes that occurred in 2015 in the northern Lake Baikal region: July 7 Upper Akuli earthquake (Mw=4.6) with the epicenter at the headwaters of the Akuli River, and September 25 Gulonga-I (Mw=4.7) and December 13 Gulonga-II earthquakes (Mw=4.6) with the epicenters near the mountain lakes Gulonga. Instrumental and macroseismic data on these seismic events are reported. A seismic moment tensor, calculated from surface wave records, shows normal fault focal mechanisms for Upper Akuli and Gulonga-II earthquakes and strike-slip movements in the source of the Gulonga-I seismic event. The results obtained could be used in further studies of seismic zoning and seismic hazard assessment in the northern Lake Baikal region.

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New geophysical data from the northern Cordillera: preliminary interpretations and implications for the tectonics and deep geology

Canadian Journal of Earth Sciences ◽

10.1139/e94-081 ◽

1994 ◽

Vol 31 (6) ◽

pp. 891-904 ◽

Cited By ~ 20

Author(s):

C. Lowe ◽

R. B. Horner ◽

J. K. Mortensen ◽

S. T. Johnston ◽

C. F. Roots

Keyword(s):

Gravity Data ◽

Field Studies ◽

Geophysical Data ◽

Fault System ◽

Tectonic Activity ◽

Denali Fault ◽

The North ◽

The Pacific ◽

Proterozoic Basement ◽

Seismic Sections

In this paper we analyze recently acquired geophysical data from the northern Cordillera and their relation to the mapped geology. A prominent gravity high (> −45 mGal (1 Gal = 1 cm/s2)) coincides with a magnetic low and an aseismic region in west-central Yukon where the underlying geology is dominated by quartzo-feldspathic rocks having moderate densities. Extension (~15%), magmatic underplating, and accretion of the anomalous region onto oceanic crust are three possible explanations.Magnetic, gravity, and seismicity data all show significant differences in the physical state of the crust on either side of the Tintina Fault and, together with geological data indicating large offset, suggest it was once a major crustal-scale strike-slip fault. The new gravity data also delineate an arcuate zone of steep gradients (up to 1.4 mGal/km) in the miogeocline, which may correlate with a west-dipping Proterozoic basement ramp mapped on deep seismic sections farther to the north and a transition from thin (east) to thick sediment cover (west). Seismicity data show that current tectonic activity is concentrated along the Pacific – North America plate margin in southwestern Yukon and adjacent Alaska and, although there is a marked decrease in activity inland of this margin, notable concentrations occur along the Denali Fault System and in the eastern miogeocline. There is a distinct absence of earthquakes in parts of the Selwyn Basin and in the northern Yukon–Tanana Terrane. Limited field studies suggest activity is confined to the upper 10–15 km of the crust.

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Joint Interpretation of Geophysical Results and Geological Observations for Detecting Buried Active Faults: The Case of the “Il Lago” Plain (Pettoranello del Molise, Italy)

Remote Sensing ◽

10.3390/rs13081555 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1555

Author(s):

Rosa Nappi ◽

Valeria Paoletti ◽

Donato D’Antonio ◽

Francesco Soldovieri ◽

Luigi Capozzoli ◽

...

Keyword(s):

Seismic Tomography ◽

Active Faults ◽

Low Frequency ◽

Normal Fault ◽

Seismic Source ◽

Fault System ◽

Normal Faults ◽

Macroseismic Data ◽

Epicentral Area ◽

Seismogenic Source

We report a geophysical study across an active normal fault in the Southern Apennines. The surveyed area is the “Il Lago” Plain (Pettoranello del Molise), at the foot of Mt. Patalecchia (Molise Apennines, Southern Italy), a small tectonic basin filled by Holocene deposits located at the NW termination of the major Quaternary Bojano basin structure. This basin, on the NE flank of the Matese Massif, was the epicentral area of the very strong 26 July, 1805, Sant’Anna earthquake (I0 = X MCS, Mw = 6.7). The “Il Lago” Plain is bordered by a portion of the right-stepping normal fault system bounding the whole Bojano Quaternary basin (28 km long). The seismic source responsible for the 1805 earthquake is regarded as one of the most hazardous structures of the Apennines; however, the position of its NW boundary of this seismic source is debated. Geological, geomorphological and macroseismic data show that some coseismic surface faulting also occurred in correspondence with the border fault of the “Il Lago” Plain. The study of the “Il Lago” Plain subsurface might help to constrain the NW segment boundary of the 1805 seismogenic source, suggesting that it is possibly a capable fault, source for moderate (Mw < 5.5) to strong earthquakes (Mw ≥ 5.5). Therefore, we constrained the geometry of the fault beneath the plain using low-frequency Ground Penetrating Radar (GPR) data supported by seismic tomography. Seismic tomography yielded preliminary information on the subsurface structures and the dielectric permittivity of the subsoil. A set of GPR parallel profiles allowed a quick and high-resolution characterization of the lateral extension of the fault, and of its geometry at depth. The result of our study demonstrates the optimal potential of combined seismic and deep GPR surveys for investigating the geometry of buried active normal faults. Moreover, our study could be used for identifying suitable sites for paleoseismic analyses, where record of earthquake surface faulting might be preserved in Holocene lacustrine sedimentary deposits. The present case demonstrates the possibility to detect with high accuracy the complexity of a fault-zone within a basin, inferred by GPR data, not only in its shallower part, but also down to about 100 m depth.

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Estimate hydrodynamic connectivity and probability of contamination through Lagrangian experiments in a high resolution shelf sea model

10.5194/egusphere-egu2020-20673 ◽

2020 ◽

Author(s):

Michele Bendoni ◽

Carlo Brandini ◽

Maria Fattorini ◽

Chiara Lapucci ◽

Carlo Pretti

Keyword(s):

High Resolution ◽

Initial Conditions ◽

Low Resolution ◽

Reanalysis Dataset ◽

North West ◽

The North ◽

Port Area ◽

Shelf Sea ◽

Resolution Model ◽

One Year

Coastal areas are experiencing an increasing anthropic pressure worldwide, especially due to port activities. In addition, valuable ecosystems such as Marine Protected Areas (MPA) might be located close to ports and be potentially subject to pollutant driven by the local current pattern. It is then fundamental to develop tools to analyze and quantify the tendency of a MPA to be affected by generic pollutant released from a port. Present work is based on a series of Lagrangian experiments carried out on a domain containing the port of Livorno and the Meloria Sholas MPA, located in the Tuscany Archipelago (Italy). The flow field employed to force the experiments is obtained from a downscaling modelling chain implemented with the 3D ROMS software. The top level is a 1.2 km low-resolution model covering the North-West portion of the Mediterranean basin which feeds with a one-way nesting algorithm a 400 m mid-resolution model for the Tuscany Archipelago, extending West of Corsica Island and up to the Gulf of Genova. The inner level of the modelling chain is a 50 m high-resolution coastal model (offline nesting) which covers the area of Meloria Shoals, the port, and their surroundings. Hydrodynamic simulations are carried out for one year. Initial conditions are provided by the CMEMS (1/24&#176; res) model Analysis, as well as boundary conditions for the low-resolution model. Atmospheric forcing comes from the downscaling of the ERA-5 reanalysis dataset, consisting on the BOLAM model implemented on a 7 km grid of the Med-CORDEX domain, in which the MOLOCH model is nested on a 2.5 km spaced grid. Lagrangian numerical experiments are carried out considering the consecutive release of passive particles in the port area, at finite intervals for one year, following the trajectories for ten days. To estimate the degree of hydrodynamic connectivity between the port and the MPA and give a measure of the probability of contamination, the &#8220;oceanographic distance&#8221; is computed in several ways from the calculated trajectories. Preliminary results show the main transport pattern is mostly distributed alongshore, making the MPA less connected to the port compared to areas placed at the same distance.

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Seismic stratigraphy of the Vendean-Armorican platform of the French Atlantic shelf: new insights into the history of the North Atlantic ocean

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.181.1.37 ◽

2010 ◽

Vol 181 (1) ◽

pp. 37-50

Author(s):

Pedro Huerta ◽

Jean-Noël Proust ◽

Pol Guennoc ◽

Isabelle Thinon

Keyword(s):

High Resolution ◽

Atlantic Ocean ◽

Sea Level ◽

North Atlantic ◽

North Atlantic Ocean ◽

Passive Margin ◽

Tectonic Activity ◽

Marine Deposits ◽

The North ◽

The North Atlantic

Abstract The evolution of the North-Atlantic Ocean from its rifting stage during the Upper Jurassic until the present-day passive margin is recorded by the sedimentary wedge of eastern French-Atlantic platform. The study of a dense network of high resolution seismic profiles on the Vendean-Armorican platform (VAP) obtained during INSU-CNRS cruise “Geovend”, led to the characterization of the architecture of the sediment wedge preserved between the coast and Armorican margin shelf edge. This sediment wedge lies on a substratum composed of metamorphic and magmatic rocks of Palaeozoic age (Ub). The sediment wedge comprises six seismic units (U1-U6) bounded by regional unconformities: Jurassic marine succession (U1), Upper Cretaceous marine rocks (U2), Eocene-Oligocene marine deposits of the incipient VAP (U3), Miocene (U4) and Plio-Quaternary (U5) marine deposits overlain by the last sea-level rise ravinement deposits (U6). Above the basal unconformity at the top of Ub, the units are bounded by angular unconformities (top of U1, U2, U3), truncation with channel incision (top U4) or planar marine ravinement (top of U5) surfaces. Most of these unconformities are due to the tectonic activity of the bay of Biscay during the Mesozoic including (1) the North Atlantic rifting during the Jurassic to Early Cretaceous, (2) the propagation of the ocean crust and counterclockwise rotation of the Iberian block during the Aptian-Albian to Coniacian (magnetic anomaly 33–34) producing troughs at the top of U1 filled by downlapping U2 sediment wedges, (3) the Alpine compression at the origin of folding and faulting and the unconformable deposition of U3, and (4) the late compressive deformation during the Miocene that affected U4. The VAP acquires its actual configuration during U4. Sedimentation on the platform was then affected by climatically-controlled relative sea-level changes (U5 to U6) that forced U5 shelf margin sediment deposition above an incised unconformity and subsequently overlain by U6 transgressive sediment blanketing. One of the main interest of the VAP area is the existence of pre- to post-rift units that helps to decipher with high resolution seismics the long-lived evolution of the Armorican margin. Such units are preserved because of the specific characters of this area located on the flank of the former Aquitaine basin (near the “celtaquitaine” flexure) and the presence of the Rochebonne basement high. The VAP thus displays most of the tectonosedimentary evolution of the West Atlantic margins. This paper would however constitute a basis for comparisons to other examples around the Atlantic ocean and then contribute to strengthen the running models of passive margin evolution.

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MORPHOLOGICAL RESPONSE TO THE DEEP WATERWAY PROJECT AROUND THE CHANGJIANG ESTUARY, CHINA

Coastal Engineering Proceedings ◽

10.9753/icce.v32.posters.11 ◽

2011 ◽

Vol 1 (32) ◽

pp. 11

Author(s):

Lingzhi Pan ◽

Pingxing Ding ◽

Jianzhong Ge

Keyword(s):

Sediment Transport ◽

High Resolution ◽

Phase I ◽

Morphological Change ◽

Changjiang Estuary ◽

Morphological Response ◽

The Changjiang Estuary ◽

The North ◽

High Resolution Bathymetry ◽

Evolution Trend

Changjiang Estuary is characterized by complex branches and outlets (North Branch, North Channel, North Passage and South Passage). The relatively shallow bathymetry around the mouth limits the navigational potentials (Fig.1). The Deep Waterway Project (DWP) was carried out in the North Passage of South Channel for the purpose of deepening the navigational channel from 7.0m in July 1998 to 8.5m in July 2001 (Phase I), 10.0m in May 2005 (Phase II) and 12.5m in May 2010 (Liu et al. 2004). In addition to dredging, two dykes were constructed to reduce the sediment transport from Jiuduansha and Hengsha Shoals into North Passage. A set of groins was built with connection to dykes for the purpose of strengthening the currents in the middle of channel, which helps the maintenance of the navigational capability. The construction has significantly changed the local bathymetry in the Changjiang Estuary and within the channel. The high-resolution bathymetry measurements were made over seasons. An evolution trend of the morphological change is revealed, which is discussed in this paper.

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