Joint Inversion Method Research Articles

High-Resolution Cooperate Density-Integrated Inversion Method of Airborne Gravity and Its Gradient Data

Airborne (or satellite) gravity measurement is a commonly used remote sensing method to obtain the underground density distribution. Airborne gravity gradiometry data have a higher horizontal resolution to shallower causative sources than airborne gravity anomaly, so joint exploration of airborne gravity and its gradient data can simultaneously obtain the anomaly feature of sources with different depths. The most commonly used joint inversion method of gravity and its gradient data is the data combined method, which is to combine all the components into a data matrix as mutual constraints to reduce ambiguity and non-uniqueness. In order to obtain higher resolution results, we proposed a cooperate density-integrated inversion method of airborne gravity and its gradient data, which firstly carried out the joint inversion using cross-gradient constraints to obtain two density structures, and then fused two recovered models into a result through Fourier transform; finally, data combined joint inversion of airborne gravity, and gradient data were reperformed to achieve high-resolution density result using fused density results as a reference model. Compared to the data combined joint inversion method, the proposed cooperate density-integrated inversion method can obtain higher resolution and more accurate density distribution of shallow and deep bodies meanwhile. We also applied it to real data in the mining area of western Liaoning Province, China. The results showed that the depth of the skarn-type iron mine in the region is about 900–1300 m and gives a more specific distribution compared to the geological results, which provided reliable data for the next exploration plan.

Joint inversion of gravity and magnetic data using correspondence maps with application to geothermal fields

SUMMARY Current geophysical joint inversion methods can be roughly divided into structurally or property driven. While structural coupling plays a key role in fully heterogeneous environments, it is blind to the actual physical properties, which limit its application. On the other hand, approaches based on direct property-correlations promise strong coupled models using petrophysical linkages derived from rock physics or through the search for cross-property relationships in the objective function directly, for example, fuzzy-clusters or correspondence maps. We apply a correspondence maps (CM) methodology to the joint estimation of density and magnetization in 3-D environments using gravity and magnetic data. CM joint inversion has yet to be applied to the specific combination of gravity and magnetic data, nor compared to other approaches like cross-gradient coupling or fuzzy-clustering. The CM searches for cross-property functional relationships; it has the potential to allow a gradual property variation that is not restricted to a predetermined number of homogeneous zones. We tested the algorithm using two illustrative synthetic examples to analyse the compositional and geometrical improvements and thoroughly investigate its capacity to recover a study model based on potential features in a geothermal scenario using polynomials. We investigated the case of using lower and higher polynomials than required for recovering the second synthetic model. The nature of the inversion suggested instability when high-grade polynomials were used, which was successfully overcome by gradually increasing the number of coefficients. The strategy was satisfactorily implemented to the field data. We applied the algorithm over the Los Humeros geothermal field in Mexico and fit a quadratic relationship between density and magnetization that exhibits two main zones consistent with previous works. The first one contains relatively low density and high magnetization. The second zone contains low density and low magnetization values. In this last zone, we emphasize that an observed link between low density, low magnetization, and major fault zones with high relevance to geothermal exploration is resulting from joint inversion, only. We achieved an enhanced petrophysical and structural integrated subsurface imaging in synthetic and field cases at the expense of slightly increased RMS misfit value.

P-P and Dynamic Time Warped P-SV Wave AVA Joint-Inversion With ℓ1–2 Regularization

S-wave velocity and mass density, which are two essential parameters in distinguishing lithology and hydrocarbon detection, are very difficult to retrieve even when long-offset gather data are used. P-P and P-SV waves joint inversion has been verified as an effective tool to accurately extract such fluid related parameters. However, registering the travel-time of P-P and P-SV waves on the identical coordinate is a significant but knotty problem for the joint inversion. Therefore, an improved strategy of prestack seismic joint inversion is proposed for accurately transforming the recorded data to elastic-parameter-based interpretive information. First, to overcome the weaknesses of artificial strenching and the local cross correlation-based method, a nonstrenching and globally optimal registration algorithm, i.e., dynamic time warping (DTW), is exploited to match the P-P and P-SV waves. Then, a new method has been developed for the joint inversion method by combining the logarithmic absolute-criterion-based misfit function with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-2</sub> norm-based penalty, which can significantly improve the vertical resolution and stability of inversion results. The numerical examples demonstrate that the DTW algorithm can obtain better registered results than the conventional method. Moreover, the proposed joint inversion method performs better than the conventional prestack inversion in both resolution and accuracy, especially for the S-wave velocity.

Spatiotemporal Characteristics of Reservoir-Induced Earthquakes Using P-Wave Velocity Structures

In this study, through the seismic phase observation report obtained by a river reservoir seismic network from September 2012 to July 2015, the joint inversion method of source and velocity structure is employed, combined with the regional seismic geological environment data. Such method gives the P-wave velocity structure of different sections in the reservoir area and tries to find out the impact range of the reservoir water depth. And the impact of reservoir water infiltration on crustal medium is discussed. The obtained location results show that the earthquake activity is mainly concentrated in the first reservoir tail and the second reservoir head. As such, the spatial distribution characteristics of the recorded earthquakes are given, and the resolution results of detection board at different depths are speculated and discussed.

Joint inversion of electromagnetic measurements for the determination of water saturation profiles in concrete structures

Water saturation profiles in concrete are essential to assess its durability and can be determined using non-destructive techniques, especially the electric and the capacitive methods. In this paper, we propose a new inversion scheme where both resistivity and permittivity measurements are inverted jointly to retrieve the saturation profile. The finite element method is used to model the measurements in 3D, the concrete having a saturation profile with depth, represented by a continuous model taking the form of a Weibull curve with four parameters. A non-linear least-squares optimization based on the Levenberg-Marquardt scheme is developed for the inversion of measurements. Results show that information gathered from both measurements enriches the reconstructed profile, leading to a more reliable estimation of saturation profiles. We believe that the joint inversion method herein developed could lead to the study of more complex phenomena, such as the coupled water-chloride ingress.

Research on joint inversion method of seismic compressional and shear waves from ocean-bottom nodes

Research on joint inversion method of seismic compressional and shear waves from ocean-bottom nodes

S wave Velocity Structure of the Crust and Upper Mantle Beneath Shanxi Rift, Central North China Craton and its Tectonic Implications

AbstractThe Shanxi rift is located in the central part of the North China Craton (NCC). With strong tectonic deformation and intense seismic activity, its crust‐mantle deformation and deep structure have always attracted wide attention. Using teleseismic events observed in a dense network of 610 temporary and 127 permanent stations in the central NCC, we obtained the crust‐mantle S wave velocity structures by the joint inversion method of receiver functions and surface wave dispersion data. Our results show that the crust thickens in the northern part of the Shanxi rift (41 km) and thins in the southern part (35 km). The Taiyuan and Linfen basins, located in the central part, have high‐velocity zones in the lower crust and upper mantle; beneath the Yuncheng basin in the south, there are low‐velocity zones in the lower crust and uppermost mantle (30–80 km); the Datong basin, located in the northern part of the rift, exhibits a wide range of low‐velocity anomalies in the middle to lower crust and upper mantle. We speculate that the destruction of the NCC and associated lithospheric thinning had a significant impact on the southern part of the rift, but is still in its early stage in the central part, which retains most of the craton features. An upwelling of the asthenospheric magma occurred beneath the western part of the Datong basin. The horizontal deflection of the asthenospheric flow causes low‐velocity anomalies in its surrounding area, which is consistent with LAB topography.

Joint inversion for 1-D crustal seismicS- andP-wave velocity structures with interfaces and its application to the Wabash Valley Seismic Zone

SUMMARYInterfaces are important part of Earth’s layering structure. Here, we developed a new model parametrization and iterative linearized inversion method that determines 1-D crustal velocity structure using surface wave dispersion, teleseismic P-wave receiver functions and Ps and PmP traveltimes. Unlike previous joint inversion methods, the new model parametrization includes interface depths and layer Vp/Vs ratios so that smoothness constraint can be conveniently applied to velocities of individual layers without affecting the velocity discontinuity across the interfaces. It also allows adding interface-related observation such as traveltimes of Ps and PmP in the joint inversion to eliminate the trade-off between interface depth and Vp/Vs ratio and therefore to reduce the uncertainties of results. Numerical tests show that the method is computationally efficient and the inversion results are robust and independent of the initial model. Application of the method to a dense linear array across the Wabash Valley Seismic Zone (WVSZ) produced a high-resolution crustal image in this seismically active region. The results show a 51–55-km-thick crust with a mid-crustal interface at 14–17 km. The crustal Vp/Vs ratio varies from 1.69 to 1.90. There are three pillow-like, ∼100 km apart high-velocity bodies sitting at the base of the crust and directly above each of them are a low-velocity anomaly in the middle crust and a high-velocity anomaly in the upper crust. They are interpreted to be produced by mantle magmatic intrusions and remelting during rifting events in the end of the Precambrian. The current diffuse seismicity in the WVSZ might be rooted in this ancient distributed rifting structure.

Estimation of near-surface shear-wave velocity by joint inversion of dispersion and HVSR curves of Rayleigh waves from multicomponent active-seismic records

The multichannel analysis of surface waves (MASW) method has been widely used for near-surface geophysical and geotechnical studies by using the dispersive characteristics of Rayleigh waves to determine subsurface shear-wave velocity. Commonly, Rayleigh waves are obtained only from the vertical component of P-SV waves. However, the multimodal Rayleigh waves estimated from the horizontal (radial) component data have a different energy distribution compared with those estimated from the vertical component data. The horizontal-to-vertical spectral ratio (HVSR) of Rayleigh waves can be calculated from multicomponent active-seismic records after mode separation. The HVSR peak and trough frequencies are very sensitive to model parameters. We propose to estimate near-surface shear-wave velocity by joint inversion of dispersion and HVSR curves of Rayleigh waves from multicomponent active-seismic records. The proposed joint inversion method can combine the strengths of MASW and HVSR analysis methods. A synthetic example demonstrates that our proposed joint inversion method can provide better constrained and more reliable S-wave velocity in the shallow subsurface.

Cross-gradient based 3D sparse joint inversion using smoothness constraint for gravity and magnetic data of Jalalabad Hematite ore

Cross-gradient based joint inversion method is one of the very useful methods for reduction of non-uniqueness and elimination of lacks of reconstructed models using separate inversion. This method have also some deficiencies against its advantages. It needs too much time when the dimension of problem is large and sometimes it's not runnable. In this paper data space method, as a fast procedure for inversion of some matrices in inversion process, was represented and cross-gradient based joint inversion algorithm supported by this method was developed in MATLAB software. To investigate the capability of code, a synthetic model include three cubes with various dimensions and depth extend was used. At first the calculated gravity and magnetic anomalies of this synthetic model were separately inverted using data space inversion method. Then these synthetic gravity and magnetic data were jointly inverted using the improved 3D inversion algorithm along with smoothness constraint. The obtained results showed significant improvements in the output model with the same conditions of separate data inversion. These improvements were in delineation of location and depth estimating aspects and also capability of code performance to recover such number of model’s parameters. After validating of results, the proposed routine was applied for 3D joint inversion of the gravity and magnetic data of one Hematite area around Jalalabad iron mine in Zarand city (Kerman province). Comparison of the inversion results with those obtained by drilling, validates correctness and ability of the presented algorithm even when we encounters with deficiency of data.

The present‐day stress field in the Zagros Fold-Thrust Belt of Iran, from inversion of focal mechanisms

The knowledge about spatial variation of stress field is an important step in the identification of geodynamic and seismotectonic characteristics. Inversion of focal mechanism solutions is one of the most common methods for determination of stress field and the shape ratio in a tectonic region. In this paper, Iterative Joint Inversion method is used to determine principal stress axes from earthquake focal mechanisms in the Zagros continental collision zone of Iran. In order to determine the influence of dependent events on the inversion results, the declustering process is carried out by the Urhammer's method. The area is divided into seven subzones according to the stress field heterogeneity in the Zagros region. In each subzone, the trends of principal stress axes, the orientation of maximum horizontal stress, stress regime and the shape ratio are determined. The results show that the compressional stress direction averages NNE-SSW that accord with the current convergence between the Arabian plate and Iranian micro-continent. A gradual counterclockwise rotation of the compressional axis is also concluded which is compatible with spatial changes in the Arabian–Eurasian convergence paths along the Zagros. The stress regime of most of the subzones is deduced as the Transpression that reflects oblique convergence. The orientation of the maximum principal stress (σ1) show the lowest uncertainty in respect to the intermediate (σ2) and minimum (σ3) principal stress axes. The shape ratio error in all zones are less than 6 and 7.2 percent before and after implementing exclusion respectively, which indicate this error increases with removing the dependent events in all zones except for zone 3.

Transdimensional Markov Chain Monte Carlo joint inversion of direct current resistivity and transient electromagnetic data

SUMMARYJoint inversion of multiple geophysical data sets with complementary information content can significantly reduce the non-uniqueness inherent to each individual data set and, therefore, can improve subsurface characterization. Gradient-based joint inversion methods depend on the choice of model regularization and usually produce one single optimal model, and rely on linearization to estimate model parameter uncertainty. However, a quantitative evaluation of the parameter uncertainty of the derived model parameters is crucial for reliable data interpretation. In this study, we present a transdimensional Markov Chain Monte Carlo (MCMC) method for the joint inversion of direct current resistivity and transient electromagnetic data, which provides a rigorous assessment of the uncertainty associated with the derived model. The transdimensional property of the algorithm allows the number of unknown model parameters to be determined adaptively by the data. This usually favours models with fewer parameters through the parsimony criterion of the Bayesian method by choosing suitable prior distributions. In this paper, we demonstrate that the transdimensional MCMC method combines complementary information contained in each data set and reduces the overall uncertainty using synthetic examples. Furthermore, we successfully applied the new joint inversion scheme to field data from Azraq, Jordan. The transdimensional MCMC inversion results are in good agreement with the results obtained by deterministic inversion techniques. From the MCMC inversion results we identified the thickness of a basalt formation and a conductive zone, which were uncertain and not interpreted in prior studies, adding to the geological interpretation.

Six Major Historical Earthquakes in the Seoul Metropolitan Area during the Joseon Dynasty (1392–1910)

ABSTRACTEarthquake records in the historical literature provide valuable information on the seismic hazard potentials for long recurrence times. The Seoul metropolitan area is the center of the economy and infrastructure in South Korea. Six major earthquakes that occurred around the Seoul metropolitan area during the Joseon dynasty in 1392–1910 are analyzed using a probabilistic joint inversion method based on seismic damage records and earthquake-felt reports. The inversion yields sets of event locations and magnitudes with probabilities. The joint inversion method is validated with synthetic and instrumentally observed data sets. The historical earthquakes are found to be located around the Seoul metropolitan area. The magnitudes of the earthquakes range from ML 5.3 to 6.8 at the peak probabilistic locations. These historical earthquakes suggest considerable seismic hazard potentials in the Seoul metropolitan area.

Crustal Deformations of the Central North China Craton Constrained by Radial Anisotropy

AbstractSituated in a transition zone between the western and eastern North China Craton (NCC), the central NCC exhibits complex dynamics features. Significant lithosphere thinning is observed beneath the eastern NCC and the northern segment of the central NCC. To study how the crust responses to the distinct lateral variations of the lithospheric mantle, we develop a method for joint inversion of Rayleigh and Love dispersion curves based on a transverse‐isotropic (or radial anisotropy) medium and obtain a 3‐D crustal radial anisotropy model. The results reveal significant heterogeneities along the Cenozoic Fenhe‐Weihe Rift (FWR). In the northern FWR, the discretely distributed lower crust positive anisotropy and upper crust negative anisotropy suggest the rifting is mainly dominated by the active mantle upwelling resulting in the Datong volcanoes. Similarly, the northern segment of the Taihang Mountain is also strongly affected by the magmatic activities and exhibits different anisotropy properties compared to its central‐to‐southern counterpart. Based on the negative anisotropy observed in the middle‐to‐lower crust beneath most parts of the Taihang Mountain, we speculate that a lower‐crust compression model can be applied to the Taihang Mountain, which is totally different to that of the adjacent Bohai Bay Basin. Possibly, the root of the Taihang Mountain is pushed by the westward moving lower crust coupled with the lateral escaping mantle flow beneath the Bohai Bay Basin. The Taihang Mountain and the Bohai Bay Basin are formed in similar tectonic environments, but are deformed in different ways.

Joint inversion of quality factor based on upgoing and downgoing waves

Quality factor Q is a key parameter describing seismic wave attenuation. Estimating Q accurately is important to seismic data processing and reservoir characterization. Downgoing and upgoing waves are coming from above and below the receiver containing the strata information, respectively. Downgoing wave has always been the key in Q inversion, while the upgoing wave is seldom used. Thus, the information contained in the upgoing wave is not fully utilized, leading to problems of multi-solution and low accuracy. To fix these problems, this study proposes a joint inversion method of Q, which uses both upgoing and downgoing waves. The nonlinear relation among the upgoing wave, downgoing wave, and Q value is jointly used to construct an objective function, which measures the energy difference between the actual and calculated amplitude spectra. As the energy between upgoing and downgoing waves is not balanced, to balance the weight of the two kinds of waves in Q inversion, a weight coefficient is used to adaptively control the weight of them. The optimal Q can be estimated by minimizing the objective function. Numerical simulation results indicate that the proposed method can reduce the effect of frequency band selection, and provide more accurate results. The application on field data demonstrates that good results can be achieved, and the estimated Q has great potential in reservoir characterization.

Joint inversion of logging-while-drilling multipole acoustic data to determine formation shear-wave transverse isotropy

Seismic-wave anisotropy has long been an important topic in the exploration and development of unconventional reservoirs, especially in shales, which are commonly characterized as transversely isotropic ([TI] or vertical TI [VTI]) media. At present, the shear-wave (S-wave) TI properties have mainly been determined from monopole Stoneley- or dipole flexural-wave measurements in wireline acoustic logging, but the feasibility of those obtained from logging-while-drilling (LWD) acoustic data needs to be established. We have developed a joint inversion method for simultaneously determining formation S-wave transverse isotropy and vertical velocity from LWD multipole acoustic data. Our theoretical analysis shows that the presence of anisotropy strongly influences LWD Stoneley- and quadrupole-wave dispersion characteristics. Although the monopole Stoneley and quadrupole waves are sensitive to the formation S-wave TI parameters, they suffer from the typical nonuniqueness problem when using the individual-wave data to invert parameters alone. Thus, the respective dispersion data can be jointly used to estimate the formation S-wave TI properties. By the joint inversion, the nonuniqueness problem in the parameter inversion can also be effectively alleviated. The feasibility of the method has been verified by the processing results of theoretical synthetic data and field LWD acoustic-wave data. Therefore, the result offers an effective method for evaluating VTI formation anisotropy from acoustic LWD data.

Imaging the subsurface using induced seismicity and ambient noise: 3-D tomographic Monte Carlo joint inversion of earthquake body wave traveltimes and surface wave dispersion

SUMMARYSeismic body wave traveltime tomography and surface wave dispersion tomography have been used widely to characterize earthquakes and to study the subsurface structure of the Earth. Since these types of problem are often significantly non-linear and have non-unique solutions, Markov chain Monte Carlo methods have been used to find probabilistic solutions. Body and surface wave data are usually inverted separately to produce independent velocity models. However, body wave tomography is generally sensitive to structure around the subvolume in which earthquakes occur and produces limited resolution in the shallower Earth, whereas surface wave tomography is often sensitive to shallower structure. To better estimate subsurface properties, we therefore jointly invert for the seismic velocity structure and earthquake locations using body and surface wave data simultaneously. We apply the new joint inversion method to a mining site in the United Kingdom at which induced seismicity occurred and was recorded on a small local network of stations, and where ambient noise recordings are available from the same stations. The ambient noise is processed to obtain inter-receiver surface wave dispersion measurements which are inverted jointly with body wave arrival times from local earthquakes. The results show that by using both types of data, the earthquake source parameters and the velocity structure can be better constrained than in independent inversions. To further understand and interpret the results, we conduct synthetic tests to compare the results from body wave inversion and joint inversion. The results show that trade-offs between source parameters and velocities appear to bias results if only body wave data are used, but this issue is largely resolved by using the joint inversion method. Thus the use of ambient seismic noise and our fully non-linear inversion provides a valuable, improved method to image the subsurface velocity and seismicity.

Approach on Joint Inversion of Electromagnetic and Acoustic Data Based on Structural Constraints

Because of strong nonlinearity, it is always a challenge to acquire fine resolution reconstruction results for electric strong scatterers with high contrasts using electromagnetic (EM) data. Many electric strong scatterers have weak nonlinearity in acoustic inversion. To make full use of the advantages of acoustic inversion, two joint inversion methods based on the structural constraints to reconstruct electric strong scatterers using EM and acoustic data are proposed in this article. These two methods utilize the framework of the subspace-based optimization method (SOM). In the inversion process, one of the methods utilizes a cross-gradient function to link the EM and the acoustic inversions, enforcing the structural similarity between the permittivity and the sound velocity. The second method is to utilize the reconstruction result of acoustic data as initial structural information for the EM inversion process. Compared with conventional separate SOM, these two methods achieve finer EM reconstruction for electric strong scatterers. Both structure and contrast values are well reconstructed. The efficiency and the robustness of the methods are validated through numerical experiments.

Effective elastic thickness of the lithosphere from joint inversion in western China and its implications*

The western China lies in the convergence zone between Eurasian and Indian plates. It is an ideal place to study the lithosphere dynamics and tectonic evolutions on the continental Earth. The lithospheric strength is a key factor in controlling the lithosphere dynamics and deformations. The effective elastic thickness (Te) of the lithosphere can be used to address the lithospheric strength. Previous researchers only used one of the admittance or coherence methods to investigate the Te in the western China. Moreover, most of them ignored the internal loads of the lithosphere during the Te calculation, which can produce large biases in the Te estimations. To provide more reliable Te estimations, we used a new joint inversion method that integrated both admittance and coherence techniques to compute the Te in this study, with the WGM2012 gravity data, the ETOPO1 topographic data, and the Moho depths from the CRUST1.0 model. The internal loads are considered and investigated using the load ratio (F). Our results show that the joint inversion method can yield reliable Te and F values. Based on the analysis of Te and F distributions, we suggest (1) the northern Tibetan Plateau could be the front edge of the plate collision of Eurasian and Indian plates; (2) the southern and part of central Tibetan Plateau have a strong lithospheric mantle related to the rigid underthrusting Indian plate; (3) the southeastern Tibetan Plateau may be experiencing the delamination of lithosphere and upwelling of asthenosphere.

Joint inversion of Rayleigh and Love wave dispersion curves for improving the accuracy of near-surface S-wave velocities

High-frequency surface-wave techniques are extensively employed for the determination of S-wave velocities of near-surface materials. The absence of the measured phase velocity dispersion curves at specific frequency band, however, is common in the real world, which may cause inaccurate S-wave velocity by inversion. Additionally, surface-wave phase velocities are relatively insensitive to S-wave velocities under the abnormal high or low velocity layer, so it is difficult for surface-wave techniques to obtain S-wave velocities in irregular models which contain an (or several) abnormal layer(s). Based on significantly different sensitivity frequency bands of Rayleigh and Love wave phase velocities, a joint inversion method of Rayleigh and Love wave dispersion curves was proposed by the conjugate gradient algorithm. We used synthetic models to test the effectiveness of the developed method. Numerical modeling results revealed that: (1) S-wave velocities acquired by joint inversion of Rayleigh and Love wave phase velocities were more accurate than that by individual inversion in the case of lacking surface-wave dispersion data; (2) joint inversion efficiently improved the accuracy of S-wave velocities of irregular models. A real-world example verified the validity in application of the proposed approach.