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

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.

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

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.

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

2020 ◽  
Vol 7 (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.

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

2020 ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo
Keyword(s):  
Gravity Data ◽  
Active Faults ◽  
Normal Fault ◽  
Japan Sea ◽  
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 activity. It is, however, difficult to understand the overall tectonic character of the region due to the thick sediments in this region. We estimated the depth and the structure of the basement top in the Mikawa Bay Region through the analysis of gravity data, compiling publicly available gravity data and our own gravity measurements in the central part of the region. The gravity basement map shows the deepening of the basement top from the Nishi-Mikawa Plain to the Chita Peninsula. Two-dimensional modeling constrains the orientation of the Utsumi and Takahama faults. The fact that the basement top structure related to the Kou Fault is insignificant in the gravity data indicates that the geometry of the Kou Fault is small relative to that of the Utsumi Fault. The basement top structure from the Nishi-Mikawa Plain to the Chita Peninsula reveals a half graben structure bounded by the Utsumi Fault. The inverse motion of the Utsumi Fault, which underwent normal faulting during the Miocene followed by recent reverse faulting, is interpreted to reflect the inversion tectonics of the half graben. The timing of the inversion tectonics, i.e. the reverse faulting of the Miocene normal fault, can be compared to an episode of basin inversion observed at the eastern margin of the Japan Sea, northeastern Japan. The Takahama Fault in the center 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.

scholarly journals Correction to: Half-graben inversion tectonics revealed by gravity modeling in the Mikawa Bay region, Central Japan

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Ayumu Miyakawa ◽  
Tomoya Abe ◽  
Tatsuya Sumita ◽  
Makoto Otsubo
Keyword(s):  
Gravity Modeling ◽  
Inversion Tectonics ◽  
Central Japan ◽  
Half Graben

An amendment to this paper has been published and can be accessed via the original article.

Structural interpretation of the Rukwa Rift, Tanzania

Geophysics ◽  
1988 ◽  
Vol 53 (6) ◽  
pp. 824-836 ◽  
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.

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

2021 ◽  
Author(s):  
Virginie Gaullier ◽  
Gaël Lymer ◽  
Bruno Vendeville ◽  
Frank Chanier
Keyword(s):  
Sedimentary Cover ◽  
Vertical Motion ◽  
Normal Fault ◽  
Lateral Flow ◽  
Salt Tectonics ◽  
Distal Margin ◽  
Tyrrhenian Sea ◽  
Vertical Movements ◽  
Half Graben ◽  
Tyrrhenian Basin

<p>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 décollement, 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.</p>

scholarly journals Role of tectonic burial and temperature on the inversion of inherited extensional basins during collision

2016 ◽  
Vol 153 (5-6) ◽  
pp. 811-826 ◽  
Author(s):  
MANFRED LAFOSSE ◽  
ALEXANDRE BOUTOUX ◽  
NICOLAS BELLAHSEN ◽  
LAETITIA LE POURHIET
Keyword(s):  
Friction Coefficient ◽  
Internal Friction ◽  
Normal Fault ◽  
Geothermal Gradient ◽  
Western Alps ◽  
Fault Reactivation ◽  
Thin Body ◽  
Burial Depth ◽  
Basin Inversion ◽  
Half Graben

AbstractThe style of inversion of inherited extensional basins in the Western Alps is investigated through thermo-mechanical modelling. Two-dimensional models consist of a half-graben embedded in a relatively strong crust (basement) and filled with weak syn-rift sediments (cover). We investigate the relative influence of the internal friction (µ) of the basin-bounding normal fault, tectonic burial (h) under an overlying nappe and the geothermal gradient. We use a viscoplastic model with symmetrical shortening. The inherited normal fault is implemented as a curved thin body with a variable friction coefficient (µ) ranging from 0.1 to 0.6. The style of basin inversion is controlled at shallow depth by the internal friction coefficient, whose influence decreases with the increase of both burial depth and geothermal gradient. With increasing burial and/or geothermal gradient, fault reactivation is inhibited and distributed deformation in the basement induces the vertical extrusion of the cover. The basin inversion is accompanied by distributed deformation in the cover and by the shearing of the basin and basement interface. The results are consistent with the style of inversion of inherited half-grabens in the external Western Alps, where no significant fault reactivation occurred owing to tectonic burial underneath the Alpine internal units during the early Alpine collision.

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

Geosciences ◽  
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.

scholarly journals Basement Mapping of the Fucino Basin in Central Italy by ITRESC Modeling of Gravity Data

Geosciences ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 398
Author(s):  
Federico Cella ◽  
Rosa Nappi ◽  
Valeria Paoletti ◽  
Giovanni Florio
Keyword(s):  
Seismic Activity ◽  
Site Response ◽  
Gravity Data ◽  
A Priori ◽  
Central Italy ◽  
Gravity Anomalies ◽  
Gravity Modeling ◽  
Ground Shaking ◽  
Sedimentary Evolution ◽  
Fucino Basin

Sediments infilling in intermontane basins in areas with high seismic activity can strongly affect ground-shaking phenomena at the surface. Estimates of thickness and density distribution within these basin infills are crucial for ground motion amplification analysis, especially where demographic growth in human settlements has implied increasing seismic risk. We employed a 3D gravity modeling technique (ITerative RESCaling—ITRESC) to investigate the Fucino Basin (Apennines, central Italy), a half-graben basin in which intense seismic activity has recently occurred. For the first time in this region, a 3D model of the Meso-Cenozoic carbonate basement morphology was retrieved through the inversion of gravity data. Taking advantage of the ITRESC technique, (1) we were able to (1) perform an integration of geophysical and geological data constraints and (2) determine a density contrast function through a data-driven process. Thus, we avoided assuming a priori information. Finally, we provided a model that honored the gravity anomalies field by integrating many different kinds of depth constraints. Our results confirmed evidence from previous studies concerning the overall shape of the basin; however, we also highlighted several local discrepancies, such as: (a) the position of several fault lines, (b) the position of the main depocenter, and (c) the isopach map. We also pointed out the existence of a new, unknown fault, and of new features concerning known faults. All of these elements provided useful contributions to the study of the tectono-sedimentary evolution of the basin, as well as key information for assessing the local site-response effects, in terms of seismic hazards.

scholarly journals Stretching and Contraction of Extensional Basins With Pre-Rift Salt: A Numerical Modeling Approach

2021 ◽  
Vol 9 ◽  
Author(s):  
Pablo Granado ◽  
Jonas B. Ruh ◽  
Pablo Santolaria ◽  
Philipp Strauss ◽  
Josep Anton Muñoz
Keyword(s):  
Hanging Wall ◽  
Structural Evolution ◽  
Extension Rate ◽  
Rift Basins ◽  
Basin Inversion ◽  
Accommodation Space ◽  
Basement Faults ◽  
Original Distribution ◽  
Thrust Belts ◽  
Half Graben

We present a series of 2D thermo-mechanical numerical experiments of thick-skinned crustal extension including a pre-rift salt horizon and subsequent thin-, thick-skinned, or mixed styles of convergence accompanied by surface processes. Extension localization along steep basement faults produces half-graben structures and leads to variations in the original distribution of pre-rift salt. Thick-skinned extension rate and salt rheology control hanging wall accommodation space as well as the locus and timing of minibasin grounding. Upon shortening, extension-related basement steps hinder forward propagation of evolving shallow thrust systems; conversely, if full basin inversion takes place along every individual fault, the regional salt layer is placed back to its pre-extensional configuration, constituting a regionally continuous décollement. Continued shortening and basement involvement deform the shallow fold-thrust structures and locally breaches the shallow décollement. We aim at obtaining a series of structural, stratigraphic and kinematic templates of fold-and-thrust belts involving rift basins with an intervening pre-rift salt horizon. Numerical results are compared to natural cases of salt-related inversion tectonics to better understand their structural evolution.

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