Interactions between salt tectonics and crustal tectonics on the Eastern Sardinian Margin (Western Tyrrhenian Sea)

The METYSS project (Messinian Event in the Tyrrhenian from Seismic Study) is based on high-resolution seismic data acquired along the Eastern Sardinian margin. The main aim is to study the Messinian Salinity Crisis (MSC) in the Western Tyrrhenian Basin, but we also investigated the thinning processes of the continental crust and the timing of crustal vertical movements across this backarc domain. Our first results shown that rifting ended before the MSC, but that crustal activity persisted long after the end of the rifting. This has been particularly observed on the proximal margin, the East-Sardinia Basin, where the Mobile Unit (MU, mobile Messinian salt) is thin or absent. In this study, we examined the distal margin, the Cornaglia Terrace, where the MU accumulated during the MSC and acted as a d&#233;collement, thus potentially decoupling the basement from the sedimentary cover. Our observations provide evidence for lateral flow and gravity gliding of the salt and its brittle sedimentary overburden along local basement slopes generated by the post-MSC tilting of some basement blocks formerly generated during the rifting. We also investigated an intriguing wedge-shaped body of MU located in a narrow N-S half graben bounded to the west by a major, east-dipping, crustal normal fault. Classically, one could think that this salt wedge is related to the syn-tectonics deposition of the MU, but we propose an original scenario, in which the post-rift vertical motion of the major fault has been cushioned by lateral flow of an initially tabular salt layer, leaving the supra-salt series apparently unaffected by the crustal motions of the basement. We tested this scenario by comparing natural data and physical (analogue) modelling data. Our results reveal that salt tectonics provides a powerful tool to understand the deep crustal tectonics of the margin and to constrain the timing of vertical motions in the Western Tyrrhenian Basin, results that can be applied to rifted salt-bearing margins worldwide.

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Half-graben inversion tectonics revealed by gravity modeling in the Mikawa Bay Region, Central Japan

10.21203/rs.3.rs-29592/v3 ◽

2020 ◽

Author(s):

Ayumu Miyakawa ◽

Tomoya Abe ◽

Tatsuya Sumita ◽

Makoto Otsubo

Keyword(s):

Gravity Data ◽

Sedimentary Cover ◽

Active Faults ◽

Normal Fault ◽

Gravity Modeling ◽

Inversion Tectonics ◽

Central Japan ◽

Basin Inversion ◽

Reverse Faulting ◽

Half Graben

Abstract The Mikawa Bay Region, central Japan, is characterized by many active faults recording Quaternary activities. It is, however, difficult to understand the overall tectonic character of the region due to a thick sedimentary cover. We report the first finding of Neogene basin inversion in southwest Japan by estimating the depth and structure of the basement surface in the Mikawa Bay Region by analyzing gravity data. Our gravity basement map and two-dimensional density-structure model automatically determined using the genetic algorithm revealed a half-graben bounded on the south by the north-dipping Utsumi Fault. The motion of the Utsumi Fault, which inverted from normal faulting during the Miocene to recent reverse faulting, indicated the inversion of the half-graben. The timing of the inversion of the fault motion, i.e., the reverse faulting of the Miocene normal fault, can be compared with an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the southwestern part of the Nishi–Mikawa Plain is considered to have formed as a result of the backthrust of the Utsumi Fault under inversion tectonics. If the Takahama Fault is indeed the backthrust fault of the Utsumi Fault, the root of the Takahama Fault may be deep such that the Takahama Fault is seismogenic and linked to the 1945 Mikawa earthquake.

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Half graben inversion tectonics revealed by gravity modeling in the Mikawa Bay Region, Central Japan

10.21203/rs.3.rs-29592/v2 ◽

2020 ◽

Author(s):

Ayumu Miyakawa ◽

Tomoya Abe ◽

Tatsuya Sumita ◽

Makoto Otsubo

Keyword(s):

Gravity Data ◽

Sedimentary Cover ◽

Active Faults ◽

Normal Fault ◽

Gravity Modeling ◽

Inversion Tectonics ◽

Central Japan ◽

Basin Inversion ◽

Reverse Faulting ◽

Half Graben

Abstract The Mikawa Bay Region, central Japan, is characterized by many active faults recording Quaternary activities. It is, however, difficult to understand the overall tectonic character of the region due to a thick sedimentary cover. We report the first finding of Neogene basin inversion in southwest Japan by estimating the depth and structure of the basement surface in the Mikawa Bay Region by analyzing gravity data. Our gravity basement map and two-dimensional density-structure modeling revealed a half graben bounded on the south by the north-dipping Utsumi Fault. The motion of the Utsumi Fault, which inverted from normal faulting during the Miocene to recent reverse faulting, indicated the inversion of the half graben. The timing of the inversion of the fault motion, i.e. the reverse faulting of the Miocene normal fault, can be compared with an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the southwestern part of the Nishi–Mikawa Plain is considered to have formed as a result of the backthrust of the Utsumi Fault under inversion tectonics. If the Takahama Fault is indeed the backthrust fault of the Utsumi Fault, the root of the Takahama Fault may be deep such that the Takahama Fault is seismogenic and linked to the 1945 Mikawa earthquake.

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Half-graben inversion tectonics revealed by gravity modeling in the Mikawa Bay Region, Central Japan

Progress in Earth and Planetary Science ◽

10.1186/s40645-020-00376-6 ◽

2020 ◽

Vol 7 (1) ◽

Cited By ~ 1

Author(s):

Ayumu Miyakawa ◽

Tomoya Abe ◽

Tatsuya Sumita ◽

Makoto Otsubo

Keyword(s):

Gravity Data ◽

Sedimentary Cover ◽

Active Faults ◽

Normal Fault ◽

Gravity Modeling ◽

Inversion Tectonics ◽

Central Japan ◽

Basin Inversion ◽

Reverse Faulting ◽

Half Graben

AbstractThe Mikawa Bay Region, central Japan, is characterized by many active faults recording Quaternary activities. It is, however, difficult to understand the overall tectonic character of the region due to a thick sedimentary cover. We report the first finding of Neogene basin inversion in southwest Japan by estimating the depth and structure of the basement surface in the Mikawa Bay Region by analyzing gravity data. Our gravity basement map and two-dimensional density-structure model automatically determined using the genetic algorithm revealed a half-graben bounded on the south by the north-dipping Utsumi Fault. The motion of the Utsumi Fault, which inverted from normal faulting during the Miocene to recent reverse faulting, indicated the inversion of the half-graben. The timing of the inversion of the fault motion, i.e., the reverse faulting of the Miocene normal fault, can be compared with an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the southwestern part of the Nishi–Mikawa Plain is considered to have formed as a result of the backthrust of the Utsumi Fault under inversion tectonics. If the Takahama Fault is indeed the backthrust fault of the Utsumi Fault, the root of the Takahama Fault may be deep such that the Takahama Fault is seismogenic and linked to the 1945 Mikawa earthquake.

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Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

Geosciences ◽

10.3390/geosciences11020102 ◽

2021 ◽

Vol 11 (2) ◽

pp. 102

Author(s):

Paraskevi Nomikou ◽

Dimitris Evangelidis ◽

Dimitrios Papanikolaou ◽

Danai Lampridou ◽

Dimitris Litsas ◽

...

Keyword(s):

Fault Zone ◽

Seismic Activity ◽

Volcanic Rocks ◽

Active Tectonics ◽

Normal Fault ◽

Aegean Sea ◽

Northern Margin ◽

The North ◽

Eastern Aegean ◽

Half Graben

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

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Paleoseismological analysis of the Rurrand fault near Jülich, Roer Valley graben, Germany: Coseismic or aseismic faulting history?

Netherlands Journal of Geosciences – Geologie en Mijnbouw ◽

10.1017/s0016774600023817 ◽

2001 ◽

Vol 80 (3-4) ◽

pp. 155-169 ◽

Cited By ~ 18

Author(s):

K. Vanneste ◽

K. Verbeeck

Keyword(s):

Normal Fault ◽

Historical Earthquakes ◽

Early Pleistocene ◽

Moderate Activity ◽

Rhine River ◽

Fault Creep ◽

Vertical Movements ◽

Roer Valley Graben ◽

Fault Displacement ◽

German Part

AbstractA first trench has been excavated for paleoseismological analysis in the German part of the Roer Valley graben, which has experienced several historical earthquakes with a maximum intensity up to VIII on the MSK-scale.The trench has exposed the Rurrand fault as a complex fault zone with at least five separate, SW-dipping, normal fault strands displacing an early Pleistocene terrace of the Rhine river by more than 7 m. The major part of the observed deformation was produced during or after deposition of an overlying unit of stratified loess of middle Weichselian to probably Saalian age. The faulting history is shown to be episodic, with different fault strands active at different times. Growth faulting that would be indicative of continuous, aseismic fault motion has not been observed. Our stratigraphic control is not sufficient to constrain the timing and to provide evidence of the coseismic nature for each observed fault displacement. However, two units of structureless, gravelly loess are interpreted as the result of extensive solifluction triggered by two large surface-rupturing events. This is suggested by the position of these units, which is controlled by the main faults, and by their remarkably young age (< 400 cal. BC), indicated by radiocarbon and OSL datings and by the presence of historic brick fragments. At least two faults show moderate activity that is even younger. Our interpretation is not in agreement with earlier hypotheses that ongoing vertical movements of circa 1 mm/a in the German part of the Lower Rhine graben are the result of aseismic fault creep, but is in line with the results of similar investigations on the southwestern border fault of the Roer Valley Graben in Belgium, which demonstrates the need for further paleoseismological research in this region. The Rurrand fault is presently experiencing aseismic slip on its superficial portion, induced by extensive groundwater lowering for mining purposes. This ongoing deformation seems to be expressed in the trench as diffuse bundles of anastomosing cracks extending up to, and in some cases even into the plough zone, rather than as sharp fault planes which are typical of older, tectonic fault movements.

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Measurable impact of river incision on rift tectonics

10.5194/egusphere-egu21-5193 ◽

2021 ◽

Author(s):

Jean-Arthur Olive ◽

Luca Malatesta ◽

Mark Behn ◽

Roger Buck

Keyword(s):

Numerical Simulations ◽

Hanging Wall ◽

Normal Fault ◽

Climatic Conditions ◽

Natural Variability ◽

Surface Processes ◽

Tectonic Deformation ◽

Plate Boundaries ◽

River Incision ◽

Half Graben

Models that couple tectonics and surface processes commonly predict that efficient erosion and sedimentation help focus crustal deformation onto fewer, longer-lived faults. However, because their geomorphic parameters are difficult to calibrate against real landscapes, the sensitivity of tectonic deformation to a realistic range of surface process efficiencies remains poorly known. Here we model the growth of structurally simple half-graben structures subjected to fluvial incision of specified efficiency and sedimentation. Numerical simulations predict that infinitely-efficient erosion and deposition (i.e., complete surface leveling) can more than double the maximum offset reached on a master normal fault before crustal strain localizes elsewhere. Further, leveling footwall relief tends to promote the migration of strain towards the hanging wall to form new grabens instead of horsts.&#160;&#160; &#160; &#160; &#160; &#160;To test whether the efficiency of river incision can vary sufficiently across real rifts to exert a control on tectonic styles, we analyze the profiles of rivers draining half-graben footwalls and horst blocks in the Basin & Range, Taupo, Rio Grande, and East African Rift. We adapt the standard methodology of equilibrium river profile analysis to account for spatial variations in uplift expected from crustal flexure in a fault-bounded block. Erosional efficiency (EE) is defined as the inverse of the (dimensionless) slope of uplift- and drainage area-corrected river elevation plots. &#160;Measured EEs range between ~0.1 and ~4, reflecting natural variability in lithology, climate, and uplift rates across sites. Incorporating EEs within this documented range in numerical simulations, we find that increasing EE can increase the maximum throw on half-graben master faults by ~50%. Changing EE also affects the geometry of subsequent faults, with lower EEs favoring the transition from half-graben to horsts. These models predict that rifting in a colder, stronger continental crust is less sensitive to surface processes and requires even lower EE to develop horst structures. Our simulations are consistent with a compilation of EE, crustal strength proxies, and fault characteristics across real rift zones. These results suggest that natural variability in climatic conditions and surface erodibility has a measurable impact on the tectonic makeup of Earth's plate boundaries.

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The post-Caledonian thermo-tectonic evolution of Fennoscandia

10.5194/egusphere-egu21-8199 ◽

2021 ◽

Author(s):

Peter Japsen ◽

Paul F. Green ◽

Johan M. Bonow ◽

James A. Chalmers ◽

Ian Duddy ◽

...

Keyword(s):

Middle Jurassic ◽

Middle Triassic ◽

Sedimentary Cover ◽

Late Carboniferous ◽

Early Miocene ◽

Plate Tectonic ◽

Dynamic Topography ◽

Vertical Movements ◽

Regional Tectonic ◽

Atlantic Margin

Here we present apatite fission-track analysis (AFTA) data and thermal history interpretations in 332 samples from outcrops and boreholes at elevations between +2 and -6 km relative to sea level across Fennoscandia. The data define episodes of burial and exhumation which involved deposition and removal of kilometre-scale thicknesses of sediment as well as denudation of the underlying basement rocks that resulted in the formation of peneplains of different age and characteristics.&#160; Many of these episodes correlate with similar episodes over a much wider region, and this argues for regional tectonic control, related to plate-tectonic processes.Post-Caledonian development of Fennoscandia involved five dominant episodes of exhumation, beginning in late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene times.&#160; These episodes affected not only the present-day Atlantic margin but also the continental interior which is considered by many to represent a stable cratonic region because of the low relief and limited remnants of sedimentary cover. Pronounced offsets in the magnitude of the pre-Cenozoic episodes over short distances occur close to the Atlantic margin, and around the Oslo Rift, attesting to the tectonic origin of these episodes.&#160; In contrast, the Middle Triassic and mid-Cretaceous episodes display little variation over vast regions in the interior. Yet even here, our results show that the vertical movements involved deposition and removal of substantial sedimentary covers.&#160;The late Carboniferous, Middle Triassic and Middle Jurassic episodes can be linked with the break-up of Pangaea.&#160; The mid-Cretaceous episode correlates with a global plate reorganization.&#160; The early Miocene episode appears to be earlier than analogous episodes in Greenland, and it is not yet clear how these episodes fit into the pattern of plate-tectonic forces.&#160; The youngest tectono-thermal episode to affect Fennoscandia began in the early Pliocene and is only revealed by AFTA data from a few deep boreholes. But this episode had a major impact in shaping the present-day topography on both sides of the Atlantic and may have been driven by dynamic support from the Iceland Plume.A key aspect of the paleo-thermal episodes identified in this study is that they involve both deposition and removal of kilometre-scale thicknesses of sediment (i.e. subsidence and uplift), rather than progressive emergence and monotonic cooling of the continents as assumed in many studies.&#160; Dynamic topography and far-field transmission of stress thus appear to be likely candidates for driving the ups and downs of both marginal and interior regions.&#160;

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Deep structures of the southern Tyrrhenian basin and P-wave residuals at Messina

Bulletin of the Seismological Society of America ◽

10.1785/bssa0650041013 ◽

1975 ◽

Vol 65 (4) ◽

pp. 1013-1021

Author(s):

Antonio Bottari

Keyword(s):

Upper Mantle ◽

P Wave ◽

Tyrrhenian Sea ◽

Travel Times ◽

Deep Earthquakes ◽

First Motion ◽

Southern Tyrrhenian Sea ◽

Epicentral Location ◽

Foregoing Result ◽

Tyrrhenian Basin

Abstract In this article, P travel-time residuals for the Messina station are analyzed in order to investigate the Tyrrhenian upper mantle, which is considered to be crossed by a lithospheric slab. A first set of 24 residuals derived from deep earthquakes of the southern Tyrrhenian Sea show early arrivals of, on the average, −1.3 sec at Messina. In addition, these negative residuals are associated with initial motion of the dilatation type. On the contrary, the few deep earthquakes which produce, as first motion, a compression at the Messina station, are associated with late arrivals of about 1 sec. These results are considered and discussed in order to analyze the hypocentral mechanism and P-wave transmission through the lithospheric slab. A second and wider analysis is then extended to 206 earthquakes which have, with respect to Messina, an epicentral location in the distance range 16° to 103° and azimuthal orientation Z in the interval 180° to 380°. The first conclusion from this analysis is that the P travel times observed at Messina for epicentral distances in the range 20° to 103° and 245° ≦ Z ≦ 380° are generally 0.5 to 3 sec less than those given in the Jeffreys-Bullen tables. Finally, a further improvement on the foregoing result has been obtained. This gives further confirmation of the consistency of regional variations of the P travel times with a slab model for the Tyrrhenian deep structures. As a matter of fact, the comparison between the travel times of Messina and a standard provided by observations in the stations of Rome and Trieste confirms early arrivals of about 1 sec on the seismic paths which cross the upper mantle in the southern Tyrrhenian region.

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Structural interpretation of the Rukwa Rift, Tanzania

Geophysics ◽

10.1190/1.1442517 ◽

1988 ◽

Vol 53 (6) ◽

pp. 824-836 ◽

Cited By ~ 44

Author(s):

John W. Peirce ◽

Lev Lipkov

Keyword(s):

Gravity Data ◽

Normal Fault ◽

Gravity Models ◽

Fault System ◽

Rift System ◽

Assistance Program ◽

Density Control ◽

Half Graben ◽

Alluvial Material ◽

Petroleum Development

The Rukwa Rift lies between Lakes Tanganyika and Malawi in the western limb of the East Africa rift system. Because little was known about the rift's structure or hydrocarbon potential, Petro‐Canada International Assistance Corporation completed a 2150 station gravity survey as part of an assistance program for the Tanzanian Petroleum Development Corporation. The survey covered an area 165 km × 375 km, which included the entire rift valley and lake plus regional control on either side. Outcrops of Carboniferous‐Triassic conglomerate, coal, and limestone, as well as Cretaceous sandstone, occur along the southwestern edge of the rift. The younger section is presumed to be dominated by alluvial material. In the absence of any density control, the gravity data were modeled using clastic sedimentary fill, which yields minimum depth estimates. Alternate models with more shale in the section have also been tried. A rift model with two shale pulses corresponding to interrift times yielded maximum depths of about 10 km. An all‐shale model failed to converge because of insufficient mass contrast. The final interpretation was based on the gravity models and aeromagnetic data acquired in an earlier survey. The Rukwa Rift is a half‐graben bounded to the northeast by a listric normal fault (strike 130 degrees) with 7 km of throw. A younger fault system forms the southwestern side of the valley and creates a major structure with 3 km of relief. The divergent strike of the younger faulting appears to be related in some way to right lateral shear in the Rukwa region. The Rukwa Rift has all the elements needed to be considered highly prospective for oil from a lacustrine source. There is strong evidence to suggest that the history of the Rukwa Rift is long and complex, providing ample opportunity for establishment of such an environment. The analogy of the Sudan rifts and the reports of oil seeps elsewhere in the western rift system support such a hypothesis. All the other elements of structure, reservoir, seal, maturation, and timing can be reasonably inferred from the available information. Of course, seismic and drilling are needed to provide firm stratigraphic control to confirm these inferences.

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Basement-controlled Neogene polyphase cover thrusting and basin development along the Chianti Mountains ridge (Northern Apennines, Italy)

Geological Magazine ◽

10.1017/s0016756899002277 ◽

1999 ◽

Vol 136 (2) ◽

pp. 133-152 ◽

Cited By ~ 26

Author(s):

MARCO BONINI

Keyword(s):

Sedimentary Cover ◽

Normal Fault ◽

Northern Apennines ◽

Fault System ◽

Time Interval ◽

Tectonic Structures ◽

Quaternary Period ◽

Deformation Stages ◽

Thrust System ◽

Continental Basin

The Chianti Mountains is an important sector of an E-verging regional thrust-related fold (the so-called Tuscan Nappe) extending along the whole length of the Northern Apennines. This thrust system involves the Tuscan Sequence superposing the Macigno sandstones onto Cervarola-Falterona sandstones, both of which are sedimented in adjacent foredeep basins. Detailed field mapping and analysis of superposition relations among tectonic structures, as well as correlation between structures and syntectonic deposition, has allowed Chianti Mountain evolution to be interpreted in terms of three main stages of deformation.The D1 stage resulted in the NE-directed synsedimentary thrusting of the Macigno onto the Cervarola-Falterona sandstones, while large NE to ENE-vergent thrust-related folds developed during the two successive deformation stages (D2 and D3). Fault-propagation folds developed during the D2 stage, and were affected by the Main Chianti Mountains Thrust (MCMT) during the successive D3 stage. In particular, the D3 stage has been correlated to the development, during the Pliocene period, of the hinterland Upper Valdarno Basin, which was previously considered to be an extensional basin. In fact, this continental basin formed along the eastern margin of the Chianti Mountains, ahead of the MCMT that also produced a shortening of the basin fill. With the beginning of the Quaternary period, the tectonic regime switched to extensional, as manifested by the development of a normal fault system on the opposite basin margin.The data presented here allow us to infer that the Chianti Mountains thrust system (D2 and D3) developed during a time interval spanning from the Late Miocene (∼12 Ma) until the Late Pliocene (∼2 Ma) periods. In the Northern Apennines, polyphase thrusting recorded by cover rocks has been related to the activity of basement thrusts, which have been recently evidenced by geophysical data. In this context, the two latest stages of deformation recognised in the Chianti Mountains have been attributed to the activity of the Abetone–Cetona crustal thrust, the deformational effects of which propagated forward in the sedimentary cover.

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