Joint inversion of surface wave and gravity data reveals subbasin architecture of the Congo Basin

Geology ◽  
2021 ◽  
Author(s):  
A. Raveloson ◽  
A. Nyblade ◽  
R. Durrheim
Keyword(s):  
Joint Inversion ◽  
Gravity Data ◽  
Three Dimensional ◽  
Sedimentary Basins ◽  
Congo Basin ◽  
S Wave ◽  
African Plate ◽  
The North ◽  
Basement Faults ◽  
Structural High

We investigated the architecture of the greater Congo Basin, one of the largest and least-well-studied sedimentary basins on any continent. Seismograms from a large number of M > 4.5 earthquakes within and surrounding the African plate were used to make event-to-station Rayleigh wave group velocity measurements between periods of 5 and 100 s. Group velocities for discrete periods across the basin, obtained by inverting the event-station measurements, were jointly modeled with gravity data to obtain a three-dimensional S-wave and density model of the basin. The model corroborates the existence of two previously suggested subbasins, one to the north and one to the south, each ~8 km deep and separated by an east-west structural high. Our results favor a salt tectonics origin for the structural high but cannot rule out uplifted basement rock. The northern subbasin is offset to the west from the southern subbasin, consistent with previous studies suggesting sinistral motion along basement faults during periods of transpressional tectonics in late Neoproterozoic–early Paleozoic times.

Receiver function analyses and joint inversion with gravity data: new constraints on the Ivrea geophysical body along a high-resolution profile

2020 ◽  
Author(s):  
Matteo Scarponi ◽  
György Hetényi ◽  
Jaroslava Plomerová ◽  
Stefano Solarino ◽  
Ludovic Baron
Keyword(s):  
Receiver Function ◽  
Joint Inversion ◽  
Gravity Data ◽  
Sampling Rate ◽  
Seismic Refraction ◽  
Western Alps ◽  
Transverse Component ◽  
Reference Points ◽  
Physical Parameters ◽  
S Wave

<p>We collected new seismological and gravity data in the Val Sesia and Lago Maggiore regions in NW Italy to constrain the geometry and properties of the Ivrea Geophysical Body. This piece of lower Adriatic lithosphere is known to be at anomalously shallow depth along the inner arc of the Western Alps, yet existing seismological constraints (vintage seismic refraction data, local earthquake tomography) are spatially sparse. With the aim to reach higher spatial resolution in imaging the structure of the IGB, we analyze the seismological data with various receiver function approaches to map the main velocity discontinuities, followed by joint inversion with gravity data to fill the bulk properties of bodies with densities.</p><p>The new data acquisition consisted of two type of campaigns. For seismology, we deployed 10 broadband seismic stations (MOBNET pool, IG CAS Prague) along a linear West-East profile at 5 km spacing along Val Sesia and across the Lago Maggiore. This network continuously recorded seismic data for 27 months at 100 Hz sampling rate. For gravimetry, we compiled existing datasets and then completed the spatial gaps by relative gravity surveys, tied to absolute reference points, to achieve 1 gravity point every 1-2 km along the profile.</p><p>The receiver function (RF) analyses aim at detecting velocity increases with depth: primarily the Moho and the shallow IGB interfaces and their crustal reverberations (multiples), together with their potential dip by analyzing the transverse component RFs. Furthermore, we aim at investigating the sharpness of the velocity gradient across the discontinuities by analyzing the frequency dependence of the corresponding RF peaks. We aim at reproducing the observations by simple synthetic models.</p><p>The 2D joint inversion combines S wave velocity V<sub>S</sub> and bulk density as physical parameters to match both the seismological and gravimetry data. The relationship between the two parameters is initially chosen from the literature, but depending on the first results the relation itself may be inverted for, considering the various high-grade metamorphic rocks observed at the surface in the area, whose properties may not align with classical V<sub>S</sub>–density equations. In conclusion, we propose new constraints on the IGB, demonstrating the advantage of using multi-disciplinary geophysical observations and improved data coverage across the study area.</p>

scholarly journals Supplemental Material: Joint inversion of surface wave and gravity data reveals subbasin architecture of the Congo Basin

2021 ◽  
Author(s):  
Andriamiranto Raveloson ◽  
et al.
Keyword(s):  
Surface Wave ◽  
Joint Inversion ◽  
Gravity Data ◽  
Congo Basin

Supplemental figures illustrating the inversion, resolution, and results.<br>

Three-dimensional imaging of the Mérida Andes, Venezuela

2021 ◽  
Author(s):  
José Cruces ◽  
Oliver Ritter ◽  
Ute Weckmann ◽  
Kristina Tietze ◽  
Naser Meqbel ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Sedimentary Basins ◽  
Tectonic Plates ◽  
Fault Systems ◽  
Maracaibo Basin ◽  
The North ◽  
Oblique Convergence ◽  
The Caribbean ◽  
Major Strike ◽  
Triangular Block

&lt;p&gt;The M&amp;#233;rida Andes are a 100 km wide mountain chain that extends from the Colombian/Venezuelan border to the Caribbean coast. To the north and south, the M&amp;#233;rida Andes are bound by hydrocarbon-rich sedimentary basins. Uplift of the mountains started in the late Miocene due to oblique convergence of the Caribbean and South American tectonic plates and the north-eastwards expulsion of the North Andean Block (NAB). This tectonic interaction fostered major strike-slip fault systems, with associated high seismicity, and the partitioning of the North Andean Block into smaller tectonic units, whose interaction accelerated the uplift of the M&amp;#233;rida Andes since the Plio-Pleistocene.&lt;/p&gt;&lt;p&gt;We present the three-dimensional inversion results of broadband magnetotelluric (MT) data from 72 sites gathered along a 240 km long profile across the central part of the MA, the Maracaibo (MB), and Barinas-Apure (BAB) foreland basins. Directionality and dimensionality analyses suggested 3D structures for the MA section, with the induction vectors indicating off-profile structures, particularly at long periods. Since the distribution of sites predominantly along a single profile can have adverse effects on the outcome of the 3D inversion, we rigorously tested all model features for robustness and excluded artefacts.&lt;/p&gt;&lt;p&gt;One of the main findings is a deep connection (&gt; 10km) between the most prominent faults of the MA, the Valera and Bocon&amp;#243; fault systems, with a deep off-profile conductor to the east of our profile. We interpret this conductive structure as a detachment surface of the Trujillo Block, which is part of the NAB and whose expulsion to the NE significantly influences the present-day geodynamic evolution of western Venezuela. A conductive zone under the Maracaibo Basin correlates spatially with the location of a Bouguer low. Both geophysical anomalies may be caused by a SE tilt of the Maracaibo Triangular Block under the M&amp;#233;rida Andes, bound by the north-western thrust system which could reach depths of 30 km.&lt;/p&gt;

Correlation of gravity anomalies with Yellowknife Supergroup rocks, North Arm, Great Slave Lake

1980 ◽  
Vol 17 (11) ◽  
pp. 1506-1516 ◽  
Author(s):  
R. A. Gibb ◽  
M. D. Thomas
Keyword(s):  
Greenstone Belt ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Rock Density ◽  
The North ◽  
Great Slave Lake ◽  
Western Shore ◽  
Gravity Map

A gravity map compiled from observations made on the frozen surface of Great Slave Lake shows that the positive gravity anomaly associated with the Yellowknife greenstone belt extends offshore into the North Arm of the lake. On the western shore of Yellowknife Bay the axis of the anomaly coincides with mafic volcanic rocks of the Kam Formation. Offshore the axis continues southwards for about 10 km to the West Mirage Islands where it takes a dramatic turn to the southeast and continues for a further 60 km to the Outer Whaleback Rocks. Using the geology and rock density determinations on land for control, a three-dimensional geological model comprising a large number of prismatic blocks was derived from the gravity anomalies. In the model the simplifying assumption has been made that the greenstone belt is everywhere floored by granodiorite similar to the adjacent Western and South-east granodiorites. According to the model, mafic volcanic rocks of the Kam Formation are generally 1–3 km thick with a maximum thickness of 7 km at the mouth of Yellowknife Bay. Greywacke and mudstone of the Burwash Formation vary in thickness from 1 to 3 km. Locally these sedimentary rocks attain a thickness of 8 km but this is probably an overestimated value as they may very well be underlain by volcanic rocks of the Kam Formation. The presence of a third pluton of granodiorite flanking the belt to the southwest is also inferred from the gravity data. Previous seismic work indicated a greenstone basin with an average thickness of about 10 km. However, reexamination of the seismic records suggests that weak arrivals interpreted as originating from the base of the greenstone belt are more likely to be pulses associated with earlier arrivals.

Using basement-hosted clastic dykes as syn-rifting palaeostress indicators: an example from the basal Stoer Group, northwest Scotland

1999 ◽  
Vol 136 (3) ◽  
pp. 301-310 ◽  
Author(s):  
L. E. BEACOM ◽  
T. B. ANDERSON ◽  
R. E. HOLDSWORTH
Keyword(s):  
Sedimentary Cover ◽  
Regional Scale ◽  
Three Dimensional ◽  
Tensile Fracture ◽  
Stress Inversion ◽  
The North ◽  
Basement Rocks ◽  
Basement Faults ◽  
Half Graben ◽  
Inversion Techniques

Clastic infills of fractures (here termed clastic veins) in basement rocks immediately underlying sedimentary cover sequences can be used to date fault movements if these demonstrably occurred at the time of infilling or prior to the lithification of the entrained clastic material. This allows reconstruction of the syn-rifting palaeostress system using stress inversion techniques. During Riphean intracontinential rifting of Laurentia, the Torridonian Stoer Group sediments of northwest Scotland were deposited in half-graben basins controlled by faults, e.g. the Coigach and Clachtoll faults. At Clachtoll, northeast–southwest oblique sinistral normal faulting in the underlying basement is associated with extensive development of shear, hybrid and tensile clastic veins filled with Stoer Group sediment, infilled and deformed prior to sediment lithification. Clastic veins initially formed by gravitational infilling of sediment from above, followed by tectonically-driven, forceful hydraulic injection of fluidized sand into new fractures and reactivated pre-existing basement faults. Palaeostress axes, determined from fault lineation data and tensile fracture extension directions in the Clachtoll Fault zone, indicate west-northwest–east-southeast directed extension during rifting. On a regional scale, this implies oblique-dextral extension on the north- to north-northeast-trending Coigach Fault during Stoer Group deposition. Similar orientations, age relationships and kinematics have been obtained from pre-Torridon Group fault arrays developed in the Lewisian basement near Gairloch and Loch Maree. Overall, the faulting patterns reflect a three-dimensional strain (k≠1) formed by east-southeast–west-northwest-directed extension during deposition of the Stoer Group. More speculatitively, asymmetric density patterns of sinistral and dextral faults may indicate that rifting occurred in a regional zone of broadly north–south-oriented dextral transtension.

Joint inversion of the lithospheric density struture in the North China Craton based on GOCE satellite gravity gradient data and surface gravity data

2020 ◽  
Author(s):  
Yu Tian ◽  
Yong Wang
Keyword(s):  
North China ◽  
Joint Inversion ◽  
Gravity Data ◽  
Initial Density ◽  
Gravity Gradient ◽  
Density Structure ◽  
Satellite Gravity ◽  
Density Data ◽  
The North ◽  
Goce Satellite

&lt;p&gt;The North China Craton (NCC) is one of the oldest cratons in the world. Currently, the destruction mechanism and geodynamics of the NCC still remain controversial. All of the proposed views regarding the issues involve studying the internal density structure of the NCC lithosphere. Gravity field data are one of the most important data in regard to investigating the lithospheric density structure, the gravity gradient data and the gravity data possess their own advantages. Given the inconsistency of the on orbit GOCE satellite gravity gradient and surface gravity observation plane height, also effects of the initial density model upon of the inversion results, the joint inversion of gravity gradient and gravity are divided into two integrated processes. By using the preconditioned conjugate gradient (PCG) inversion algorithm, the density data are calculated using the preprocessed remaining gravity anomaly data. The newly obtained high resolution density data are then used as the initial density model, which can be served as the constraints for the subsequent gravity gradient inversion. Downward continuation, terrain correction, interface undulation correction and long wavelength correction are performed for the four gravity gradient tensor data(&lt;strong&gt;T&lt;/strong&gt;&lt;sub&gt;xx&lt;/sub&gt;&amp;#65292;&lt;strong&gt;T&lt;/strong&gt;&lt;sub&gt;xz&lt;/sub&gt;&amp;#65292;&lt;strong&gt;T&lt;/strong&gt;&lt;sub&gt;yy&lt;/sub&gt;&amp;#65292;&lt;strong&gt;T&lt;/strong&gt;&lt;sub&gt;zz&lt;/sub&gt;)of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite, &amp;#160;after which the remaining gravity gradient anomaly data(&lt;strong&gt;T&lt;/strong&gt;'&lt;sub&gt;xx&lt;/sub&gt;&amp;#65292;&lt;strong&gt;T&lt;/strong&gt;'&lt;sub&gt;xz&lt;/sub&gt;&amp;#65292;&lt;strong&gt;T&lt;/strong&gt;'&lt;sub&gt;yy&lt;/sub&gt;&amp;#65292;&lt;strong&gt;T&lt;/strong&gt;'&lt;sub&gt;zz&lt;/sub&gt;) are used as the new observation quantity. Finally, the ultimate lithospheric density distribution within the depth range of 0&amp;#8211;180 km in the NCC is obtained using the same PCG algorithm.&lt;/p&gt;

A Joint Inversion for Three‐dimensional P and S Wave Velocity Structure and Earthquake Locations Beneath Axial Seamount

2019 ◽  
Vol 124 (12) ◽  
pp. 12997-13020 ◽  
Author(s):  
Christian Baillard ◽  
William S.D. Wilcock ◽  
Adrien F. Arnulf ◽  
Maya Tolstoy ◽  
Felix Waldhauser
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
Joint Inversion ◽  
Three Dimensional ◽  
S Wave ◽  
Earthquake Locations ◽  
Axial Seamount
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