Estimation Of Source Parameters Research Articles

Mechanical and statistical evidence of the causality of human-made mass shifts on the Earth’s upper crust and the occurrence of earthquakes

A global catalog of small- to large-sized earthquakes was systematically analyzed to identify causality and correlatives between human-made mass shifts in the upper Earth’s crust and the occurrence of earthquakes. The mass shifts, ranging between 1 kt and 1 Tt, result from large-scale geoengineering operations, including mining, water reservoirs, hydrocarbon production, fluid injection/extractions, deep geothermal energy production and coastal management. This article shows evidence that geomechanical relationships exist with statistical significance between (a) seismic moment magnitudes M of observed earthquakes, (b) lateral distances of the earthquake hypocenters to the geoengineering “operation points” and (c) mass removals or accumulations on the Earth’s crust. Statistical findings depend on uncertainties, in particular, of source parameter estimations of seismic events before instrumental recoding. Statistical observations, however, indicate that every second, seismic event tends to occur after a decade. The chance of an earthquake to nucleate after 2 or 20 years near an area with a significant mass shift is 25 or 75 %, respectively. Moreover, causative effects of seismic activities highly depend on the tectonic stress regime in which the operations take place (i.e., extensive, transverse or compressive). Results are summarized as follows: First, seismic moment magnitudes increase the more mass is locally shifted on the Earth’s crust. Second, seismic moment magnitudes increase the larger the area in the crust is geomechanically polluted. Third, reverse faults tend to be more trigger-sensitive than normal faults due to a stronger alteration of the minimum vertical principal stress component. Pure strike-slip faults seem to rupture randomly and independently from the magnitude of the mass changes. Finally, mainly due to high estimation uncertainties of source parameters and, in particular, of shallow seismic events ( M6) seem to be triggered. The rupture propagation of triggered events might be dominated by pre-existing tectonic stress conditions.

Source Parameters of the 16 July 2010 Mw 3.4 Germantown, Maryland, Earthquake

The 16 July 2010 M 3.4 Germantown, Maryland, earthquake was the largest recorded earthquake to occur within 50 km of Washington, D.C. I estimated the source parameters of the Germantown earthquake and its M 2.1 aftershock using the empirical Green’s Function (EGF) method. I found that both earthquakes have small‐radius, high‐stress drops (static and dynamic) and high radiated energy, comparable to the source parameters of other Northeastern America earthquakes obtained using similar EGF methods. These results are consistent with previous observations that intraplate earthquakes have higher stress drops than plate‐boundary earthquakes. Higher stress drops of intraplate earthquakes may result from longer healing times and lower strain rates characteristic of intraplate regions. I estimated the frequency‐independent attenuation factor, Q , for all available source‐station paths, constraining the solution with the previously estimated source parameters, and find attenuation to be low, with constant Q varying from 743 to 3000 (maximum resolvable Q ), and 889 to 3000, for P and S waves, respectively, at hypocentral distances from around 100 to 200 km, and at frequencies between 1 and 40 Hz. The occurrence of high‐stress‐release earthquakes within regions where seismic attenuation is low makes these intraplate earthquakes potentially more damaging than their plate‐boundary counterparts.

Source Parameter Estimation and Stochastic Ground Motion Simulation Based on Recorded Accelerograms in Northwestern Vietnam

Estimated source parameters, path characteristics, and site parameters are used to simulate earthquake shaking waveforms in Vietnam. We used recorded accelerograms and point-source stochastic methodologies and included in our analysis empirical relationships between the duration of ground motion, seismic moment, and magnitude, and also those between corner-frequency, high-cut-off frequency, and moment-magnitude derived from earthquakes recorded in Vietnam and adjacent regions. Local site effects were estimated using horizontal-to-vertical spectral ratio methods. Simulated times series are compared with observed accelerograms from the 5.3 Dienbien earthquake in 2001, the first strong earthquake event to be recorded in Vietnam. Our synthetic time series of strong ground motion agrees well with both the observed waveforms and the response spectra, but suggests that PGA values obtained using current Vietnam codes may underestimate probable accelerations by 10–30%.

Joint analysis of displacement time series retrieved from SAR phase and amplitude: Impact on the estimation of volcanic source parameters

We study the impact of jointly analyzing the phase and amplitude information of a SAR dataset on the interpretation of the surface displacement over time in areas characterized by large dynamics. In particular, we compute the ground displacement time series over Fernandina and Sierra Negra calderas (Galápagos islands), by applying the Small BAseline Subset (SBAS) and the Pixel Offset (PO)‐SBAS techniques to 25 ENVISAT SAR images acquired between 2003 and 2007, when both volcanoes experienced catastrophic eruptions. By merging the SBAS and PO‐SBAS time series results the spatial density of measurements increased substantially. In addition, the joint analysis of the time series allows us to better constrain the temporal evolution of the magmatic source volume changes. Our results show that the joint use of the SBAS and PO‐SBAS approaches may help for a more correct evaluation of large deformation affecting the Earth's surface caused by eruptions, earthquakes, and landslide phenomena.

Constrained beamforming for coherence sources parameters estimation

The phased-microphone-array acquisition-system with beamforming signal processing provides sharp directivity in receiving sound source signal from desired direction. Conventional power beamforming algorithm makes use of spatial power spectrum to estimate the source locations and power by adjusting the stirring direction of the focusing beam. Although such power beamforming method shows success, there is still a research gap of power distortions caused by coherent sound fields. Furthermore the coherences between sources are still unable to identify, which could gives more detailed investigation of the source characteristics. We proposed a novel beamforming algorithm which is complex signal basis instead of signal power output basis in order to explore the phase information of the sources, moreover the coherence interference is eliminated by applying linear constrains which enhance the accuracy of the source-parameter estimation. The algorithm is further validated by numerical simulations with multiple coherence sources.

Seismicity and source parameters of moderate earthquakes in Sikkim Himalaya

In this study, we accurately relocate 360 earthquakes in the Sikkim Himalaya through the application of the double-difference algorithm to 4 years of data accrued from a eleven-station broadband seismic network. The analysis brings out two major clusters of seismicity—one located in between the main central thrust (MCT) and the main boundary thrust (MBT) and the other in the northwest region of Sikkim that is site to the devastating Mw6.9 earthquake of September 18, 2011. Keeping in view the limitations imposed by the Nyquist frequency of our data (10 Hz), we select 9 moderate size earthquakes (5.3 ≥ Ml ≥ 4) for the estimation of source parameters. Analysis of shear wave spectra of these earthquakes yields seismic moments in the range of 7.95 × 1021 dyne-cm to 6.31 × 1023 dyne-cm and corner frequencies in the range of 1.8–6.25 Hz. Smaller seismic moments obtained in Sikkim when compared with the rest of the Himalaya vindicates the lower seismicity levels in the region. Interestingly, it is observed that most of the events having larger seismic moment occur between MBT and MCT lending credence to our observation that this is the most active portion of Sikkim Himalaya. The estimates of stress drop and source radius range from 48 to 389 bar and 0.225 to 0.781 km, respectively. Stress drops do not seem to correlate with the scalar seismic moments affirming the view that stress drop is independent over a wide moment range. While the continental collision scenario can be invoked as a reason to explain a predominance of low stress drops in the Himalayan region, those with relatively higher stress drops in Sikkim Himalaya could be attributed to their affinity with strike-slip source mechanisms. Least square regression of the scalar seismic moment (M0) and local magnitude (Ml) results in a relation LogM0 = (1.56 ± 0.05)Ml + (8.55 ± 0.12) while that between moment magnitude (Mw) and local magnitude as Mw = (0.92 ± 0.04)Ml + (0.14 ± 0.06). These relations could serve as useful inputs for the assessment of earthquake hazard in this seismically active region of Himalaya.

A possible physical mechanism for the unusually long sequence of seismic activity following the 2001 Bhuj Mw7.7 earthquake, Gujarat, India

The 2001 Bhuj earthquake took place in a region away from the active plate boundaries, which qualifies this earthquake to be a typical intraplate event that claimed a death toll of 20,000 people. The aftershock sequence of this earthquake is still continuing for the last eleven years, which makes this aftershock sequence as a unique intraplate earthquake sequence in the world. This sequence is being monitored by a close digital seismic network consisting of 5–12 three-component broadband seismographs and 10–20 accelerographs that led to a homogeneous earthquake catalog consisting of precise and accurate estimates of hypocentral and source parameters. This catalog enabled us to examine the evolution of this earthquake sequence. Our study reveals a few interconnected regularities in the rate of earthquake occurrence, b-values, fractal dimensions, stress drops, and the mean earthquake depth values. We observe that a slow decrease in background seismic activity and a number of bursts in seismic activity characterize the 2001 Bhuj earthquake sequence. We also notice that the background seismic activity is associated with a monotonic decrease in the mean earthquake depth values while the bursts in seismic activity are found to be associated with a decrease in fractal dimension, b-value and mean earthquake depth estimates, and an increase in stress drop values. We propose that these bursts in seismic activity are related to the episodes of break in deep fluid circulation in the direction of the Earth's surface. The effective background permeability of the mid-crust in the 2001 Bhuj earthquake region is evaluated to be about k≈10−13m2 based on the estimates of changes in mean earthquake depth. Thus, we infer that seismogenesis of the 2001 Bhuj earthquake sequence is probably connected with active deep fluid circulation underlying the Kachchh seismic zone.

Source process and slip model of 2005 Dahuiyeh-Zarand earthquake (Iran) using inversion of near-field strong motion data

SUMMARY On 2005 February 22, the Dahuiyeh-Zarand earthquake, Mw 6.5, struck one of the most seismically active regions in south-central Iran, east of Zarand City in Kerman province, causing more than 500 fatalities. The causative fault of the 2005 Dahuiyeh-Zarand earthquake, a reverse fault, striking nearly EW and dipping to the north, was located within a mountainous region and therefore more difficult to identify compared to the range-bounded faults. Its identification, after the 2005 event, is very important for both the estimation of seismic hazard as well as for the damage and fatality functions. We have inverted six three-component near-field strong motion waveforms to obtain the complete earthquake rupture history and slip distribution. Accelerograms are bandpass filtered with 0.2–1.0 Hz, and a length of 15–17 s of the waveforms is inverted. The lack of absolute timing has been successfully overcome by estimating, from the velocity model of the region, the propagation of P and S waves from the epicentre to the stations. The final fault slip model and the estimated source parameters are able to explain the observed waveforms. The rupture is found to be bilateral with a maximum slip of 2.4 m concentrated on two asperities in the west and east sides of the nucleation point at depths of 6–12 km. The western asperity is located to the east of Zarand City and beneath the Dahuiyeh village, which might explain why the Dahuiyeh village was totally destroyed by this earthquake.

Probabilistic tsunami threat assessment of 10 recent earthquakes offshore Sumatra

SUMMARY Tsunami early warning (TEW) is a challenging task as a decision has to be made within few minutes on the basis of incomplete and error-prone data. Deterministic warning systems have difficulties in integrating and quantifying the intrinsic uncertainties. In contrast, probabilistic approaches provide a framework that handles uncertainties in a natural way. Recently, we have proposed a method using Bayesian networks (BNs) that takes into account the uncertainties of seismic source parameter estimates in TEW. In this follow-up study, the method is applied to 10 recent large earthquakes offshore Sumatra and tested for its performance. We have evaluated both the general model performance given the best knowledge we have today about the source parameters of the 10 events and the corresponding response on seismic source information evaluated in real-time. We find that the resulting site-specific warning level probabilities represent well the available tsunami wave measurements and observations. Difficulties occur in the real-time tsunami assessment if the moment magnitude estimate is severely over- or underestimated. In general, the probabilistic analysis reveals a considerably large range of uncertainties in the near-field TEW. By quantifying the uncertainties the BN analysis provides important additional information to a decision maker in a warning centre to deal with the complexity in TEW and to reason under uncertainty.

Attenuation characteristics of coda waves in Mainland Gujarat (India)

The attenuation characteristics based on coda waves of Mainland Gujarat (India) have been investigated in the present study. The broadband waveforms of 53 local earthquakes (Mw 1.1–3.3) having focal depths in the 6.0–33.6km range recorded at five stations of Mainland Gujarat region has been used for the analysis. The frequency-dependent relationships (Q=Q0fn) for coda-Q (Qc) and dependency of coda-Q on lapse time windows have been determined for the said region. The average lapse time dependent coda-Q relations estimated for the region are: Qc=(87±13)f(1.01±0.06) (lapse time: 30s), Qc=(112±20)f(0.94±0.08) (lapse time: 40s) and Qc=(120±22)f(0.76±0.07) (lapse time: 50s). The increase in Qc values with lapse time shows the depth dependence of Qc as longer lapse time windows will sample larger area. The observed quality factor is strongly dependent on frequency and lapse time, which indicates that the upper lithosphere, is more heterogeneous and seismotectonically active, while the lower lithosphere is homogeneous and relatively less active. A comparison of the coda-Q estimated for Mainland Gujarat region with those of nearby Kachchh and Saurashtra regions shows that Mainland Gujarat region is more heterogeneous. The rate of decay of attenuation (Q−1) with frequency for the relations obtained here is found to be comparable with those of other regions of the world though the absolute values differ. The obtained relations are expected to be useful for the estimation of source parameters of the earthquakes in the Mainland Gujarat region where no such relations were available earlier. These relations are also important for the simulation of earthquake strong ground motions in the region.

Distributed System for Noise Threat Evaluation Based on Psychoacoustic Measurements

An innovative system designed for the continuous monitoring of acoustic climate of urban areas was presen ted in the paper. The assessment of environmental threats is perf ormed using online data, acquired through a grid of engineered monitoring stations collecting comprehensive infor mation about the acoustic climate of urban areas. The grid of proposed devices provides valuable data for the p urpose of long and short time acoustic climate analysis. Dynamic estimation of noise source parameters and r eal measurement results of emission data are utilized to create dynamic noise maps accessible to the general public . This operation is performed through the noise source prediction employing a propagation model being o ptimized for computer cluster implementation requirements. It enables the system to generate noise maps in a reasonable time and to publish regularly map u pdates in the Internet. Moreover, the functionality of the s ystem was extended with new techniques for assessing noise-induced harmful effects on the human hearing system. The principle of operation of the dosimeter is based on a modified psychoacoustic model of hear ing and on the results of research performed with participation of volunteers concerning the impact of noise on hearing. The primary function of the dosimeter is to estimate, in real time, auditory effects which are caused by exposure to noise. The results of measurements and simulations performed by the system prototype are depicte d and analyzed. Several cases of long-term and short-term measurements of noise originating from various sou rces were considered in detail. The presented outcomes of predicted degree of the hearing threshold shift i nduced during the noise exposure can increase the awareness of harmfulness of excessive sound levels.

Online urban acoustic noise monitoring system

Concepts and implementation of the Online Urban Noise Monitoring System are presented. Principles of proposed solution used for dynamic acoustical maps creating are discussed. The architecture of the system and the data acquisition scheme are described. The concept of noise mapping, based on noise source model and propagation simulations, was developed and employed in the system. Dynamic estimation of noise source parameters utilized in the system is introduced. The details of implementation of noise map computation and visualization are presented. Advances introduced by the developed solution in the continuous noise monitoring and acoustic maps creation is in focus. The results of measurements and simulations performed by the system prototype are depicted. Noise measurements results gathered by system and created acoustic maps are compared with some other solutions in order to investigate accuracy

Evaluation of Attenuation Models for the Northeastern United States/Southeastern Canada

This study uses a database of 800 km to evaluate published attenuation models for the region. The models include functional forms that are linear (Atkinson 1989; Atkinson and Mereu 1992), bilinear (Street and Turcotte 1975; Atkinson and Mereu 1992; Boatwright and Seekins 2011) and trilinear (Atkinson and Boore 1995; Atkinson 2004) in shape. Each model is evaluated by examining residual distance trends in ground-motion data after correction of the data for the attenuation effects according to that model. None of the models provide a satisfactory description of attenuation over all distance ranges. A simple 1/ R geometric spreading model at all distances and frequencies (with an associated Q ∼ 2,000) does as well as any model in providing (on average) low bias at near-source distances while being pegged by the amplitude levels observed at regional distances—even though more complex models provide a statistically better fit to the attenuation shape overall. We need to rethink the concepts used in deriving attenuation models for the development of ground-motion prediction equations such that the model shapes are not driven so strongly by regional observations. Any attenuation model that is not significantly constrained by data at hypocentral distances from 10 to 50 km is unlikely to provide reliable estimates of near-source ground motions or source parameters.

Software to Estimate Earthquake Spectral and Source Parameters

A software (EQK_SRC_PARA) has been developed to estimate spectral parameters of earthquake source spectrum, namely: low frequency displacement spectral level (Ω0), corner frequency above which spectrum decays with a rate of 2 (fc), the cut-off frequency above which the spectrum again decays (fmax) and the rate of decay above fmax (N). A Brune’s source model [1,2] that yield a fall-off of 2 beyond corner frequency is considered with high cut-off frequency factor presented by Boore [3] that fits well for frequencies greater than fmax. The software EQK_SRC_PARA is written in MATLAB and uses input data in Sesame ASCII Format (SAF) format. The obtained spectral parameters have been used to estimate source parameters (e.g., seismic moment, source dimension and stress drop etc.) and to develop scaling laws for the study region. The cut-off frequency “fmax” can also be studied and interpreted to confirm about its origin.

Radioactive Source Estimation Using a System of Directional and Non-Directional Detectors

We derive source parameter estimation algorithms based on maximum likelihood estimation (MLE) for a system of non-directional (scintillator) and directional (CZT based Compton) radiation detectors. For multiple non-directional detectors, the joint likelihood of registered counts is maximized to estimate the source parameters. For directional detectors, the well-known List Mode Maximum Likelihood Expectation Maximization (MLEM) algorithm is extended to fuse information from multiple detectors and locate the source in Cartesian coordinates. We then develop multi-sensor fusion algorithms for a system of non-directional and directional detectors by combining MLE and MLEM algorithms. Results are presented which illustrate the behavior and performance of our proposed approaches.

Full-waveform based complete moment tensor inversion and source parameter estimation from downhole microseismic data for hydrofracture monitoring

Downhole microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracturing. Inverting for the moment tensor has gained increasing popularity in recent years as a way to understand the fracturing process. Previous studies utilize only part of the information in the waveforms, such as direct P- and S-wave amplitudes, and make far-field assumptions to determine the source mechanisms. The method is hindered in downhole monitoring, when only limited azimuthal coverage is available. In this study, we develop an approach to invert for complete moment tensor using full-waveform data recorded at a vertical borehole. We use the discrete wavenumber integration method to calculate full wavefields in the layered medium. By using synthetic data, we find that, at the near-field range, a stable, complete moment tensor can be retrieved by matching the waveforms without additional constraints. At the far-field range, we discover that the off-plane moment tensor component is poorly constrained by waveforms recorded at one well. Therefore, additional constraints must be introduced to retrieve the complete moment tensor. We study the inversion with three different types of constraints. For each constraint, we investigate the influence of velocity model errors, event mislocations, and data noise on the extracted source parameters by a Monte Carlo study. We test our method using a single well microseismic data set obtained during the hydraulic fracturing of the Bonner sands in East Texas. By imposing constraints on the fracture strike and dip range, we are able to retrieve the complete moment tensor for events in the far-field. Field results suggest that most events have a dominant double-couple component. The results also indicate the existence of a volumetric component in the moment tensor. The derived fracture plane orientation generally agrees with that derived from the multiple event location.

Estimation of Earthquake Source Parameters in the Kachchh Seismic Zone, Gujarat, India, from Strong-Motion Network Data Using a Generalized Inversion Technique

The generalized inversion of S -wave spectral amplitude data from 18 strong-motion sites in the Kachchh seismic zone, Gujarat, India, has been carried out to estimate source parameters of 38 aftershocks ( M w 2.93–5.32) from the 2001 Bhuj earthquake ( M w 7.7). The result shows that the seismic moment M and source radius r of aftershocks are between 3.1×1013 and ![Graphic][1] and 226–889 m, respectively, while stress drops ( Δσ ) vary from 0.11 to 7.44 MPa. The regression analysis between M and r shows a break in linear scaling at ![Graphic][2] . The estimated stress-drop values scatter significantly with M (![Graphic][3] ) for larger aftershocks (![Graphic][4] ) but vary in proportion with M (![Graphic][5] ) in case of smaller magnitude events. This can be due to the complex rupture process associated with relatively larger aftershocks in comparison to circular rupture for smaller events. The high stress-drop values are observed for events located on the north Wagad fault (at 15–30 km depths) and Gedi fault (at 0–5 km depths). This could be attributed to the large stress develop at the hypocentral depth as a result of high pore-fluid pressure beneath these two fault zones. The regression between M and corner frequency f c shows M is proportional to ![Graphic][6] , which is consistent for earthquakes with short rupture lengths and high stress-drop values. High stress-drop values commonly associated with the events from Kachchh and adjacent Narmada-Son lineament rift zones indicate strong potential for generating high peak ground accelerations and hence high seismic hazard. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif

Interpretation of magnetic data over tilted basement blocks: an example from the northern North Sea

ABSTRACTThis paper presents a procedure for interpreting magnetic data over tilted basement blocks. The objective of this procedure is to estimate source parameters of a tilted basement block from first‐ order derivatives of magnetic profile data. The method uses a model consisting of two superimposed infinite contacts with opposite dip. The procedure estimates the location of the crest (intersection of the two contacts) and the susceptibility contrast of the basement block from the total gradient anomaly data using a linear least‐squares method. Dip angles of the two contacts are estimated using iterative forward modelling of the tilt derivative anomaly data. The practical utility of the proposed approach is demonstrated using theoretical data and a field example from the northern North Sea.

SGRAPH (SeismoGRAPHer): Seismic waveform analysis and integrated tools in seismology

Although numerous seismological programs are currently available, most of them suffer from the inability to manipulate different data formats and the lack of embedded seismological tools. SeismoGRAPHer, or simply SGRAPH, is a new system for maintaining and analyzing seismic waveform data in a stand-alone, Windows-based application that manipulates a wide range of data formats. SGRAPH was intended to be a tool sufficient for performing basic waveform analysis and solving advanced seismological problems. The graphical user interface (GUI) utilities and the Windows functionalities, such as dialog boxes, menus, and toolbars, simplify the user interaction with the data. SGRAPH supports common data formats, such as SAC, SEED, GSE, ASCII, and Nanometrics Y-format, and provides the ability to solve many seismological problems with built-in inversion tools. Loaded traces are maintained, processed, plotted, and saved as SAC, ASCII, or PS (post script) file formats. SGRAPH includes Generalized Ray Theory (GRT), genetic algorithm (GA), least-square fitting, auto-picking, fast Fourier transforms (FFT), and many additional tools. This program provides rapid estimation of earthquake source parameters, location, attenuation, and focal mechanisms. Advanced waveform modeling techniques are provided for crustal structure and focal mechanism estimation. SGRAPH has been employed in the Egyptian National Seismic Network (ENSN) as a tool assisting with routine work and data analysis. More than 30 users have been using previous versions of SGRAPH in their research for more than 3 years. The main features of this application are ease of use, speed, small disk space requirements, and the absence of third-party developed components. Because of its architectural structure, SGRAPH can be interfaced with newly developed methods or applications in seismology. A complete setup file, including the SGRAPH package with the online user guide, is available.

Identification of strength and location of stationary point source of atmospheric pollutant in urban conditions using computational fluid dynamics model

Abstract In this paper a method is presented which allows for estimation of the location and rate of an unknown point stationary source of passive atmospheric pollutant in a complex urban geometry. The variational formulation is used in which the cost function characterizing difference of the calculated and measured concentrations is minimized with respect to source coordinates and rate. The minimization problem is solved by a direct algorithm using a source-receptor function which is calculated by solving adjoint equation. The algorithm has been implemented in ADREA-HF computational fluid dynamics code and has been applied in complex urban geometry. Validation of the algorithm has been performed by simulation of a wind tunnel experiment on atmospheric dispersion among an array of rectangular obstacles. Good results of source parameters estimation have been achieved. The measuring sensors to be used in source estimation had been randomly selected out of 244 available sensors by a specially designed random sampling algorithm which allowed for estimation of the probability of ‘good’ source term estimation with the given number of sensors. In case of ‘perfect model’ (when synthetic measurements were used for source estimation) good results were achieved with 90% or higher probability for arbitrary measurement networks consisting of 15 or more sensors even though prior estimation of source location was not used in this case. Several tests had been performed with the use of real measurements which differed by prior estimation of source location. In all cases 90% or higher probability of obtaining good solution was reached only for measurement networks consisting of 150 or more sensors. Hence further improvement of the source estimation algorithm can be achieved first of all by improving the performance of forward model.