Robust inversion of vertical electrical sounding data using a multiple reweighted least-squares method     

Milton J. Porsani  Sri Niwas †  Niraldo R. Ferreira ‡ 《Geophysical Prospecting》2001,49(2):255-264

The root cause of the instability problem of the least-squares (LS) solution of the resistivity inverse problem is the ill-conditioning of the sensitivity matrix. To circumvent this problem a new LS approach has been investigated in this paper. At each iteration, the sensitivity matrix is weighted in multiple ways generating a set of systems of linear equations. By solving each system, several candidate models are obtained. As a consequence, the space of models is explored in a more extensive and effective way resulting in a more robust and stable LS approach to solving the resistivity inverse problem. This new approach is called the multiple reweighted LS method (MRLS). The problems encountered when using the L ₁- or L ₂-norm are discussed and the advantages of working with the MRLS method are highlighted. A five-layer earth model which generates an ill-conditioned matrix due to equivalence is used to generate a synthetic data set for the Schlumberger configuration. The data are randomly corrupted by noise and then inverted by using L ₂, L ₁ and the MRLS algorithm. The stabilized solutions, even though blurred, could only be obtained by using a heavy ridge regression parameter in L ₂- and L ₁-norms. On the other hand, the MRLS solution is stable without regression factors and is superior and clearer. For a better appraisal the same initial model was used in all cases. The MRLS algorithm is also demonstrated for a field data set: a stable solution is obtained.  相似文献   

Double-difference tomography of P- and S-wave velocity structure beneath the western part of Java,Indonesia     

Shindy Rosalia  Sri Widiyantoro  Andri Dian Nugraha  Pepen Supendi 《地震科学（英文版）》2019,32(1):12-25

West Java in the western part of the Sunda Arc has a relatively high seismicity due to subduction activity and faults. In this study, double-difference tomography was used to obtain the 3D velocity tomograms of P and S waves beneath the western part of Java. To infer the geometry of the structure beneath the study area, precise earthquake hypocenter determination was first performed before tomographic imaging. For this, earthquake waveform data were extracted from the regional Meteorological, Climatological, Geophysical Agency (BMKG) network of Indonesia from South Sumatra to Central Java. The P and S arrival times for about 1,000 events in the period April 2009 to July 2016 were selected, the key features being events of magnitude > 3, azimuthal gap < 210° and number of phases > 8. A nonlinear method using the oct-tree sampling algorithm from the NonLinLoc program was employed to determine the earthquake hypocenters. The hypocenter locations were then relocated using double-difference tomography (tomoDD). A significant reduction of travel-time (root mean square basis) and a better clustering of earthquakes were achieved which correlated well with the geological structure in West Java. Double-difference tomography was found to give a clear velocity structure, especially beneath the volcanic arc area, i.e., under Mt Anak Krakatau, Mt Salak and the mountains complex in the southern part of West Java. Low velocity anomalies for the P and S waves as well as the v_P/v_S ratio below the volcanoes indicated possible partial melting of the upper mantle which ascended from the subducted slab beneath the volcanic arc.  相似文献   

CFD simulation and experimental analysis of flow dynamics and grinding performance of opposed fluidized bed air jet mill     

M. Sri Raj Rajeswari  K.A.M. Azizli  S.F.S. Hashim  M.K. Abdullah  M. Abdul Mujeebu  M.Z. Abdullah 《International Journal of Mineral Processing》2011,98(1-2):94-105

This paper presents a three dimensional Computational Fluid Dynamics (CFD) model to investigate the flow dynamics of solid–gas phases during fine grinding in an air jet mill. Alpine 100AFG fluidized bed air jet mill is considered for the study and the jet milling model is simulated using FLUENT 6.3.2 using a standard k-ε model. The model is developed in GAMBIT 2.3.16 and meshed by tet/hybrid (T-Grid) and Triangular (Pave) meshes. The effects of operating parameters such as solid feed rate, grinding air pressure and internal classifier speed on the performance of the jet mill are analyzed. The CFD simulation results are presented in the forms of dual phase vector plot, volume fraction of phases and particle trajectories during fine grinding process. The mass of ground feed entering and leaving the cyclone (underflow) is also computed by simulation. The proposed model gives realistic predictions of the flow dynamics within the jet mill. Experiments are conducted on the Alpine 100AFG jet mill to study the particle size, morphology and mass of the ground product. The numerical results are found in good agreement with the experimental results.  相似文献   

Theoretical Evaluation of Modified Wenner Array for Shallow Resistivity Exploration   总被引：1，自引：0，他引：1  

Vikas C. Goyal  Sri Niwas  Pravin K. Gupta 《Ground water》1991,29(4):582-586

  相似文献   

Developing building-damage scales for lahars: application to Merapi volcano,Indonesia     

Susanna F. Jenkins  Jeremy C. Phillips  Rebecca Price  Kate Feloy  Peter J. Baxter  Danang Sri Hadmoko  Edouard de Bélizal 《Bulletin of Volcanology》2015,77(9):1-17

  相似文献   

The 2015 eruption of Gamalama volcano (Ternate Island–Indonesia): precursor,crisis management,and community response     

Hidayat  Agung  Marfai  Muh Aris  Hadmoko  Danang Sri 《GeoJournal》2022,87(1):1-20

GeoJournal - Gamalama is an active stratovolcano on Ternate, a small volcanic island in Maluku Utara, Indonesia. Since 1510, a total of 77 eruptions have been recorded, with various impacts on the...  相似文献   

Multivariate fire risk models using copula regression in Kalimantan,Indonesia     

Najib  Mohamad Khoirun  Nurdiati  Sri  Sopaheluwakan  Ardhasena 《Natural Hazards》2022,113(2):1263-1283

Natural Hazards - Forest fires have become a national issue yearly and elicited serious attention from the government and researchers in Indonesia. Copula-based joint distribution can construct a...  相似文献   

Landslide hazard and risk assessment and their application in risk management and landuse planning in eastern flank of Menoreh Mountains,Yogyakarta Province,Indonesia     

Danang Sri Hadmoko  Franck Lavigne  Junun Sartohadi  Pramono Hadi  Winaryo 《Natural Hazards》2010,54(3):623-642

The Menoreh Mountains in Yogyakarta are severely affected by landslides. Due to the high population densities, mass movements are generally damaging and fatal. More than other Javanese mountains, the Menoreh Mountains cumulate several factors causing landslides. Therefore, it is necessary to evaluate the ways to map landslide risk in order to improve the risk mitigation. The objectives of this paper are to provide landslide hazard and risk assessment that will be useful for risk prevention and landuse planning in the Menoreh Mountains. So far, risk management has been developed by the Research Centre for Disasters Gadjah Mada University in collaboration with the Regional Development Planner (BAPPEDA), which carries out fundamental and applied researches. The results of the studies have been integrated in the risk prevention and landuse planning in order to improve the integrated landslide mitigation programme.  相似文献   

EM2INV — A finite difference based algorithm for two-dimensional inversion of geoelectromagnetic data     

P. K. Gupta  Sri Niwas  Anupma Rastogi 《Journal of Earth System Science》1999,108(4):233-253

The paper presents an efficient finite difference based 2D-inversion algorithm, EM2INV, for geoelectromagnetic data. The special features of the algorithm are

–	• optimal grid generation based on grid design thumb rules,
–	• finite domain boundary conditions,
–	• interpolation matrix that permits generation of response at observation points different from grid points,
–	• Gaussian elimination forward matrix solver, that enables reuse of already decomposed coefficient matrix,
–	• super-block notion that reduces the number of blocks with unknown resistivities and, in turn, the size of Jacobian matrix and
–	• bi-conjugate gradient matrix solver for inverse problem which circumvents the need of explicit Jacobian matrix computation.

The algorithm is tested rigorously by setting up exercises of diverse nature and of practical significance. The stability of the algorithm is established by inverting the synthetic response corrupted with Gaussian noise. The inversion experiments are aimed at studying

–	• relative performance of response functions,
–	• inversion quality of E- and B-polarization data,
–	• efficacy of single and multi-frequency data inversion,
–	• minimum number of frequencies and observation points needed for successful data inversion.

It has been observed that the Magneto-telluric data deciphers better the vertical position of the target and Geomagnetic Depth Sounding data deciphers the horizontal variations in a better way. The conductive and resistive bodies are better resolved by inversion of E- and B-polarization data respectively. The results of multi-frequency inversion imply that the increase in the number of frequencies does not necessarily enhance the inversion quality especially when the spread of observation points is sufficiently large to sense the target. The study of a minimum number of observation points highlights the importance of single point inversion that furnishes useful information about the inhomogeneity.  相似文献   

Aquifer parameter estimation from surface resistivity data   总被引：7，自引：0，他引：7  

Niwas S  de Lima OA 《Ground water》2003,41(1):94-99

This paper is devoted to the additional use, other than ground water exploration, of surface geoelectrical sounding data for aquifer hydraulic parameter estimation. In a mesoscopic framework, approximated analytical equations are developed separately for saline and for fresh water saturations. A few existing useful aquifer models, both for clean and shaley sandstones, are discussed in terms of their electrical and hydraulic effects, along with the linkage between the two. These equations are derived for insight and physical understanding of the phenomenon. In a macroscopic scale, a general aquifer model is proposed and analytical relations are derived for meaningful estimation, with a higher level of confidence, of hydraulic parameter from electrical parameters. The physical reasons for two different equations at the macroscopic level are explicitly explained to avoid confusion. Numerical examples from existing literature are reproduced to buttress our viewpoint.  相似文献