Delineating Geothermal Structure from 3D Joint Inversion of MT and Gravity Data

2020 ◽  
Author(s):  
W. Soyer ◽  
R. Mackie ◽  
S. Hallinan ◽  
F. Miorelli ◽  
A. Pavesi
Keyword(s):  
Joint Inversion ◽  
Gravity Data

Joint receiver function and gravity inversion for new constraints on the Ivrea body structure: a 2D high-resolution view along the Val Sesia profile (N. Italy).

2021 ◽  
Author(s):  
Matteo Scarponi ◽  
György Hetényi ◽  
Jaroslava Plomerová ◽  
Stefano Solarino
Keyword(s):  
High Resolution ◽  
Velocity Structure ◽  
Receiver Function ◽  
Joint Inversion ◽  
Gravity Data ◽  
Rock Physics ◽  
Receiver Functions ◽  
Gravity Inversion ◽  
European Alps ◽  
Horizontal Distance

<p>We present results from a joint inversion study of new seismic and gravity data to constrain a 2D high-resolution image of one of the most prominent geophysical anomalies of the European Alps: the Ivrea geophysical body (IGB). Our work exploits both new data and multidisciplinary a priori constraints, to better resolve the shallow crustal structure in the Ivrea-Verbano zone (IVZ), where the IGB is known to reach anomalously shallow depths and partially outcrop at the surface.</p><p>A variety of previous studies, ranging from gravity surveys to vintage refraction seismics and recent local earthquake tomographies (Solarino et al. 2018, Diehl et al. 2009), provide comprehensive but spatially sparse information on the IGB structure, which we aim at investigating at higher resolution, along a linear profile crossing the IVZ. To this purpose, we deployed 10 broadband seismic stations (MOBNET pool, IG CAS Prague), 5 km spaced along a linear West-East profile, along Val Sesia and crossing Lago Maggiore. This network operated for 27 months and allowed us to produce a new database of ca. 1000 seismic high-quality receiver functions (RFs). In addition, we collected new gravity data in the IVZ, with a data coverage of 1 gravity point every 1-2 km along the seismic profile. The newly collected data was used to set up an inversion scheme, in which RFs and gravity anomalies are jointly used to constrain the shape and the physical property contrasts across the IGB interface.</p><p>We model the IGB as a single interface between far-field constraints, whose geometry is defined by the coordinates of four nodes which may vary in space, and  density and V<sub>S</sub> shear-wave velocity contrasts associated with the interface itself, varying independently. A Markov chain Monte Carlo (MCMC) sampling method with Metropolis-Hastings selection rule was implemented to efficiently explore the model space, directing the search towards better fitting areas.</p><p>For each model, we perform ray-tracing and RFs migration using the actual velocity structure both for migration and computation of synthetic RFs, to be compared with the observations via cross-correlation of the migration images. Similarly, forward gravity modelling for a 2D density distribution is implemented and the synthetic gravity anomaly is compared with the observations along the profile. The joint inversion performance is the product of these two misfits.</p><p>The inversion results show that the IGB reaches the shallowest depths in the western part of the profile, preferentially locating the IGB interface between 3 and 7 km depth over a horizontal distance of ca. 20 km (between Boccioleto and Civiasco, longitudes 8.1 and 8.3). Within this segment, the shallowest point reaches up to 1 km below sea level. The found density and velocity contrasts are in agreement with rock physics properties of various units observed in the field and characterized in earlier studies.</p>

Joint inversion of potential-fields data over the DO-27 kimberlite pipe using a Gaussian mixture model prior

2020 ◽  
Vol 8 (4) ◽  
pp. SS47-SS62
Author(s):  
Thibaut Astic ◽  
Dominique Fournier ◽  
Douglas W. Oldenburg
Keyword(s):  
Gaussian Mixture Model ◽  
Mixture Model ◽  
Joint Inversion ◽  
Gravity Data ◽  
Physical Property ◽  
Gaussian Mixture ◽  
Kimberlite Pipe ◽  
Magnetic Data ◽  
High Porosity ◽  
Rock Types

We have carried out petrophysically and geologically guided inversions (PGIs) to jointly invert airborne and ground-based gravity data and airborne magnetic data to recover a quasi-geology model of the DO-27 kimberlite pipe in the Tli Kwi Cho (also referred to as TKC) cluster. DO-27 is composed of three main kimberlite rock types in contact with each other and embedded in a granitic host rock covered by a thin layer of glacial till. The pyroclastic kimberlite (PK), which is diamondiferous, and the volcanoclastic kimberlite (VK) have anomalously low density, due to their high porosity, and weak magnetic susceptibility. They are indistinguishable from each other based upon their potential-field responses. The hypabyssal kimberlite (HK), which is not diamondiferous, has been identified as highly magnetic and remanent. Quantitative petrophysical signatures for each rock unit are obtained from sample measurements, such as the increasing density of the PK/VK unit with depth and the remanent magnetization of the HK unit, and are represented as a Gaussian mixture model (GMM). This GMM guides the PGI toward generating a 3D quasi-geology model with physical properties that satisfies the geophysical data sets and the petrophysical signatures. Density and magnetization models recovered individually yield volumes that have physical property combinations that do not conform to any known petrophysical characteristics of the rocks in the area. A multiphysics PGI addresses this problem by using the GMM as a coupling term, but it puts a volume of the PK/VK unit at a location that is incompatible with geologic information from drillholes. To conform to that geologic knowledge, a fourth unit is introduced, PK-minor, which is petrophysically and geographically distinct from the main PK/VK unit. This inversion produces a quasi-geology model that presents good structural locations of the diamondiferous PK unit and can be used to provide a resource estimate or decide the locations of future drillholes.

3D joint inversion of seismic traveltime and gravity data: A case study

2015 ◽  
Author(s):  
Dengguo Zhou ◽  
Weizhong Wang ◽  
Jie Zhang ◽  
Daniel R.H. O'Connell
Keyword(s):  
Joint Inversion ◽  
Gravity Data

scholarly journals Pareto Joint Inversion of 2D Magnetotelluric and Gravity Data — Towards Practical Applications

2016 ◽  
Vol 64 (5) ◽  
pp. 1655-1672 ◽  
Author(s):  
Katarzyna Miernik ◽  
Adrian Bogacz ◽  
Adam Kozubal ◽  
Tomasz Danek ◽  
Marek Wojdyła
Keyword(s):  
Joint Inversion ◽  
Gravity Data ◽  
Practical Applications

Crustal Thickness and Composition of the São Paulo Plateau and Florianópolis Ridge, SE Brazilian Margin

2020 ◽  
Author(s):  
Michelle Graça ◽  
Leanne Cowie ◽  
Nick Kusznir ◽  
Natasha Stanton
Keyword(s):  
Oceanic Crust ◽  
Seismic Reflection ◽  
Joint Inversion ◽  
Gravity Data ◽  
South Atlantic ◽  
Gravity Inversion ◽  
The South ◽  
Subsidence Analysis ◽  
Base Salt ◽  
Thermal Subsidence

<p>The São Paulo Plateau (SPP) and the Florianópolis Ridge (FR), located on the Santos segment of the SE Brazilian margin in the South Atlantic, are large positive bathymetric features with a combined lateral dimension of approximately 500 km. An important question is whether they are underlain by thinned continental crust or by anomalously thick magmatic crust. Each hypothesis has implications for the breakup of the South Atlantic and the evolution of the overlying saline Santos basin.</p><p>Integrated quantitative analysis consisting of gravity inversion, RDA (residual depth anomaly) analysis and flexural subsidence analysis has been applied to a deep long-offset seismic reflection line running NW-SE across the SPP and FR. Gravity inversion predicts crustal basement thicknesses in the range of 12 to 15 km for the SPP and FR, deceasing to 7-8 km thickness at the extreme SE end of the profile. The SPP and FR are separated by a region of thinner crust approximately 80 km wide. Thinning factors from subsidence analysis for SPP and FR are typically between 0.6 and 0.7.</p><p>RDA values close to zero and a thinning factor of 1 were obtained for the region with 7-8 km thick crust at the SE end of the profile which are all consistent with normal oceanic crust rather than previously interpreted exhumed mantle. This oceanic crust is highly tectonised and corresponds to the location of the Florianópolis Fracture Zone.</p><p>Flexural backstripping and reverse thermal subsidence modelling were performed to calculate palaeo-bathymetry at breakup and give 2.5 km below sea level at the SE end of the profile consistent with this region being oceanic crust. Flexural subsidence analysis applied to base salt shows that the observed base salt subsidence requires a component of syn-tectonic subsidence as well as post-rift thermal subsidence, and that the salt was deposited while the crust was still thinning.</p><p>Joint inversion of time seismic reflection and gravity data to determine the lateral variation in basement density by comparing seismic and gravity Moho in the time domain gives a basement density under the SPP and FR of between 2600 and 2700 kg/m<sup>3</sup>. The same method gives a basement density of 900kg/m<sup>3</sup> for the oceanic crust at the SE end of the profile. The FR basement in the NW shows a basement density similar to that of the SPP while in its SE the basement density is much higher approaching 2950 kg/m3.  We interpret the relatively low basement densities of the SPP with respect to that of oceanic crust as indicating a continental rather than magmatic composition. A similar analysis to determine basement density applied to the Evain et al. (2015) seismic refraction profile in the same location also gives a SPP basement density that supports a continental composition.</p>

Integrated modelling based on shallow cross-gradient joint inversion and deep petrological approach on 2D/3D data in the Western Carpathians

2020 ◽  
Author(s):  
Ján Vozár ◽  
Vladimír Bezák ◽  
Miroslav Bielik ◽  
Javier Fullea ◽  
Max Moorkamp
Keyword(s):  
Heat Flow ◽  
Lithospheric Mantle ◽  
Joint Inversion ◽  
Gravity Data ◽  
Thermal Studies ◽  
Western Carpathians ◽  
Integrated Modelling ◽  
Geophysical Modeling ◽  
3D Data ◽  
Mineralized Water

<p>We present the integrated geophysical modelling based on magnetotelluric (MT) method included in the crustal joint inversion with gravity data performed by JIF3D code and geophysical-petrological LitMod3D thermaly-selfconsistent mantle modelling. Performed geophysical modeling is primarily based on MT and regional gravity data with supporting information from seismic methods and geothermal data like Moho and lithospheric-asthenospheric boundary (LAB) depth used for building of the starting models. The integration among geophysical models is provided by the cross-gradient coupling method for the crustal structures and in the mantle, the coupling is provided petrological relationship based on compositional, temperature and pressure distribution information. The case study is focused on 3D modelling of the seismic 2T profile in central Slovakia crossing the major Carpathian tectonic units and the contact zone between European platform and Inner Carpathian block, which coincide with Carpathian Conductivity Anomaly (CCA).</p><p>The geoelectrical models from the 3D integrated modeling image the CCA in depths of about 10 - 20km and shows great improvement in comparison with 2D MT models. The CCA exhibits 3D features represented by the offset, along the fault, in the northsouth direction in the northern part of the modelled area. The four basic segments were identified in the crust structure of the central Slovakia part of the Western Carpathians. The southernmost physically distinctive segment with high full crust conductivity caused by young volcanic activity shows the presence of the partial melt, with high geoelectrical conductivity, in the middle and lower crust caused by higher heat flow. These structures are situated to the southwest from the profile and finger type conductors indicate its penetration in northeast direction. These volcanic processes in the south are not connected with CCA presence and its origin, which is supposed to be the presence of graphite or mineralized water in mylonitized rocks on the sheer contact zones of European platform and Inner Western Carpathians.</p><p>For mantle part of the integrated models, we studied different mantle compositions and fluid content within the lithospheric mantle to explain differences in electrical and seismic LAB. The calculated petrological conductivity model shows sensitivity of MT data on the LAB depth change, the correct input of composition parameters of lithospheric mantle and thermal field. The thermal steady state approximation was used to calculate surface heat flow in the area is lower than measured and estimated values from previous thermal studies. The differences between calculated and measured heat flow is primarily caused by high radiogenic production within the crust and not by the contribution from mantle.</p>

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>

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