Gravity sources identification using continuous wavelet transform
Amin
Roshandel Kahoo
author
farshad
Salajegheh
author
text
article
2009
per
Introduction: Wavelet transform is one of the useful and suitable tools for time series and signal analysis. Nowadays wavelet transform is frequently used in geophysical data processing and interpretation, especially seismic data. However, the use of this method isn’t widespread in gravity and geomagnetic. Fedi and Quarta (1998), Martelet et al. (2001) and de Oliveira Lyrio (2004) used the wavelet transform for processing and interpretation of the potential field data. In this paper, a new method based on continuous wavelet transform for determination of depth and location of gravity anomalies is introduced.
Continuous Wavelet Transform and Gravity Source Identification: All of the time-frequency or time-scale transforms intend to show how the energy of a signal is distributed in time-frequency or time-scale plan. The Continuous Wavelet Transform (CWT) maps the time (space) domain signal into the time (space)-scale plan. The CWT of a signal is defined as the convolution of signal with a translated and scaled wavelet (Equation (1)).
(1)
where, denotes the complex conjugate, is scale, is space and is the mother wavelet. Shifted and scaled version of the mother wavelet can be computed as equation (2):
(2)
Any wavelet which is selected as the mother wavelet must meet the zero mean value condition. Mother wavelet selection can affect on the results of wavelet analysis. If the properties of the selected mother wavelet are the same as the signal, then the space-scale representation of the signal can give more useful information about the energy distribution of the signal in space-scale plan.
A buried cylinder can be seen as a rectangle in 2D view. In addition, any body in 2D can be shown by arranged rectangles. Therefore, we use the gravitational anomaly of a buried cylinder and its first and second horizontal derivatives and their vertical derivative as mother wavelets.
The gravitational anomaly of the buried cylinder can be obtained by equation (3):
(3)
where, is the gravitational constant, m is mass of the buried cylinder located at the position and depth . This wavelet does not meet the zero mean value condition and cannot be used as the mother wavelet. But its derivatives are suitable for the mother wavelet. Equations (4) to (7) are the derivatives of the gravitational the anomaly of the buried cylinder.
(4)
(5)
(6)
(7)
When we used these equations as the mother wavelet, and are not needed and is set to one.
Discussion: We tested the efficiency of the CWT method for gravity source identification on various synthetic models such as a simple cube, various type of faults, simple cubes in different depths and real data. The CWT coefficients are computed using the gravitational anomaly and its first and second horizontal derivatives. The obtained results show that the CWT coefficients obtained using first horizontal derivative of data and equations (4) and (6) can estimate precisely the depth and location of the source of gravitational anomaly.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21419_35a78c35500320ea6ec96634e10d48a8.pdf
Determination of earthquake early warning parameters, and , in southern Iran
Atie
Eshaghi
author
mohammad Reza
Gheitanchi
author
Mehdi
Zare
author
text
article
2009
per
During the past decades, attempts have been made to develop an early warning system for coming destructive earthquakes a few seconds before the ongoing ground motion. In this paper, a practical method for the early warning of earthquakes in south Iran is presented. This region is selected for study because it has high potential for generating earthquakes and has a more complete strong ground motion data set. Earthquake early warning systems have the potential to reduce the damaging effects of earthquakes by giving a few seconds to a few tens of seconds warning before the arrival of damaging ground motion. Using P-wave arrivals is the most rapid method of delivering earthquake early warning and may permit a few seconds warning of ongoing ground motion in the region.
To rapidly assess the damaging potential of an earthquake for purposes of earthquake early warning in southern Iran, we determined a ground-motion period parameter and a high-pass filtered displacement amplitude parameter from the initial 3 s of the P waveforms. The is called source parameter and is related to the magnitude of earthquakes. Our study indicates that is independent of epicentral distance up to 130 km. In practice, we calculate for distances less than 100 km. We use the peak displacement and acceleration amplitudes of the first 3 sec of the vertical-component records. At a given site, we estimate the magnitude of an event from and the peak ground-motion velocity (PGV) from .
The region of study contained 42 strong ground motion accelometers that have been deployed in the region since 1977. About 419 strong motion digital data from 209 local earthquakes that were recorded during 1977-2006 in the study region, are extracted for this study. Among these earthquakes, 194 with magnitudes greater than 3 were used for this analysis. For determination of , we used 152 waveform data with epicentral distance less than 44 km. The P-wave onset time readings were carried out by SAC software out the vertical components.
We found that the peak initial-displacement amplitude correlates well with the peak ground-motion velocity (PGV) at the same site. We selected the earthquake with that was recorded during 1975-2006 by near field strong ground motion instruments in the region, operated by the Building and Housing Research Center. The vertical components of accelerations were converted to ground velocity and displacement. The displacements are filtered with a one-way Butterworth high-pass filter with a cut-off frequency of 0.075 Hz. From the vertical components, and are computed. We found the relationship between and magnitude (M) and between and PGV for this region. These two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning around the station. The quality of data was increased by increasing the signal to noise ratio. Also, more recording stations produce less scatterings and errors. The results indicate that earthquakes with magnitudes greater than magnitude 5, have greater . Thus, by using the obtained relationships in this study, from the first 3 seconds of initial P-waves, we can estimate the magnitude of earthquakes. Also, we can clarify whether the occurring earthquake could be destructive and early warning issue might be necessary. The high seismic activity of Bandar-Abbas, the port city at the Strait of in Hormoz, in southern Iran, highlights the necessity and importance of a dense seismic network and an early warning system to be deployed in the region in order to detect the location and the magnitude of damaging earthquakes for the purposes of reducing the damaging affects of earthquakes by giving a few to a few tens of seconds warning before the arrival of damaging ground motion.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21420_45ce9cf08e0d11b8bcb8ee332fbf059e.pdf
A proposal for deformation analysis via direct computation of strain tensor elements from the time-wise changes in the distances and angles in a geodetic network
Case study: Deformation computation of the geodynamic network of Iran
Alireza
Ardalan
author
mehdi
Raoofian
author
text
article
2009
per
A method for deformation computation based on strain tensor elements, as an alternative to the usual way of application of gradient of displacement vector, is proposed. The method computes directly the strain tensor elements from the computed/observed changes in distances and angles between the stations of a geodetic network in two epochs of observations. Displacement vector which is determined from the coordinate differences with respect to “reference” and “current” states depends on the definition of coordinate system and as such can not be considered as suitable measure of deformation. On the contrary from strain tensor invariant parameters like “dilatation” and “maximum shear” can be computed which allow correct interpretation of deformation. The strain tensor can be derived from the difference between line elements of a massive body in the reference and current states as follows:
(1)
Where and are the coordinates of points in the current and reference states of the body, respectively. For computation of strain tensor directly from changes in distances and angles between stations of a geodetic network in the two states, let us start with the presentation of strain tensor as:
(2)
Therefore by substitution of equation (2) in equation (1) we have:
(3)
In the equation (3) and are the distances between geodetic network stations in the reference and current states, respectively, and , are defined as follows:
(4)
The above relations are taken from continuum mechanics, which assumes continuity in the massive body, however, in practice for the numerical computation of strain we need to discretize the body into finite element of, for example, triangular shapes in 2-D space. The triangular elements can be generated by Delaunay triangulation. Then, for each triangle three equations of the type equation (3) can be written, and via the solution of the system of equations unknown parameters can be estimated.
For the angular observation from the definition of the inner product the following equation can be developed:
(5)
Equation (5) can equivalently be written as:
(6)
where the differential elements dx and dy are defined as below:
(7)
Alternatively, the finite difference method can also be used for computation of the strain tensor in a point-wise manner as below:
(8)
where in equation (8) is the elongation in the azimuth defined as:
(9)
In this paper we numerically tested the above mentioned method for strain tensor computation by simulated examples and then applied the method to the geodynamic network of Iran.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21421_588d3823b12c9f43af59e53cd2fa8d10.pdf
Least square estimation of the bias of the measured distance between the two GRACE satellites and production of a new KBRL1B-X files versions based on GPS observations
Hasan
Hashemi Farahani
author
Alireza
Ardalan
author
text
article
2009
per
Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry mission launched in March 2002 based on its twin gravimetric satellites makes application of both High-Low (HL) and Law-Low (LL) gravimetric techniques possible. The LL is based on Satellite-to-Satellite Tracking (SST) via the one way two frequencies K-Band-Ranging between the two GRACE satellites. As a result of combination of LL and HL structures via geodesy community following gravity observables are developed: (1) Potential Difference between the two GRACE satellites based on Line of Sight (LOS) velocity using energy integral method. (2) Projection of the gravitational acceleration difference of the two GRACE satellites along the LOS, using LOS acceleration. The latter observable which can provide finer details is one of the important observation quantities of the GRACE mission. Application of this observable as a boundary data for local and regional modeling of the Earth’s gravity field provides valuable information about short and medium wavelength spectrums of the field. One of the necessary parameters for the production of this boundary data from the GRACE satellite gravimetry mission is the “inter-satellite range ?” with the bias ?b, which can be obtained from KBRL1B-X data files with 0.2 Hz rate. The unknown bias of ?, caused by phase ambiguity of the observed distance between the two GRACE satellites, is the main problem facing the application of the aforementioned information as boundary data. This issue has forced the GRACE data user’s community to compute ? at its epoch of observations from the position vectors of the two satellites, which off course has much less accuracy than the K-band measuring distance instrument. Considering the importance of the range measurement ? as boundary data for the gravimetric boundary value problems, in this paper we have offered a least squares based method for the estimation of the unknown bias ?b based on onboard GPS measurements.
Our method is based on the following steps: (1) Application of LL-SST data of GRACE mission and removal of the associated systematic errors. (2) Computation of the bias of the inter-satellite range and its accuracy via the difference between measured biased distance ? and the distance computed from GPS derived position vectors of the two satellites. (3) Detection of the occurred cycle slips within the inter-satellite range ? from the jumps in the computed biases for the consequent epochs of observations, and determination of time spans without cycle slip. (4) Computation of the range biases from the weighted mean of the computed bias for every time span without cycle slip. (5) Computation of bias free distances for every KBR observation epoch using the estimated bias from the previous step. (6) Replacing the computed bias free ranges in the original KBRL1B-X data files. Our numerical computations show that the computed bias free range based on our aforementioned method is much more accurate than direct application of the GPS derived position vectors. Besides the longer the time span without cycle slip the more accurate estimation of bias can be obtained. Finally, using the proposed method in this paper a new version of KBRL1B-X file bias free inter-satellite range observations for the time period 2002-2006 is computed.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21422_1334a163637a05a063e62d2025c7edb0.pdf
A new method for coordinate transformation between conformal map projections
s. shahram
Jazaeri Junghani
author
mohamad Ali
Sharifi
author
text
article
2009
per
Geospatial Information System (GIS) has emerged as a very powerful tool for capturing, storing, analyzing, managing, and presenting data that is linked to location. The location information, which is usually obtained from existing maps or the Global Positioning Systems (GPS), refers to different coordinate and map projection systems. Therefore, unification of the coordinate and mapping systems of the spatial information is absolutely necessary before any data processing in a GIS system.
In the classical approach, coordinate transformation among different map projection systems is performed via the reference geodetic ellipsoids. The transformation is possible if the reference ellipsoids and their corresponding datum definition parameters are known. In many cases, implementation of the classical approach is impossible due to lack of information.
Herein, we introduce an innovative approach for coordinate transformation which is completely datum-independent. It is based on the mathematical relationship between the coordinate systems. From mathematical point of view, two functions mathematically define the relationship between the horizontal coordinates in two systems. For simplicity, two polynomial functions are employed. The optimal degree of the polynomials and the unknown coefficients can be determined using the common points in two systems.
In this paper, the proposed method is theoretically developed for conformal map projections. The Cauchy-Riemann differential equations as a necessary and sufficient conformity condition are used to derive the mapping polynomials. Moreover, the validity of the new method is numerically checked on a real data set. Both the classical and the new method are employed on the data set. The achieved results show very good agreement between the classical and the new approach.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21423_4b7f7f74ce016f231a9252ab5760805e.pdf
Application of the local response method with weight function for Sea Surface Topography computations
Case study: Persian Gulf
Mohamad Reza
Salavatizadeh
author
Alireza
Ardalan
author
text
article
2009
per
Sea Surface Topography (SST) by definition is the separation between the geoid and the Mean Sea Level (MSL). The separation between the geoid and MSL is caused by various non-gravitational physical effects. If determination of the geoid as the zero point of the height systems from the tide gauge observation be the goal, it is necessary that the affect of the physical effect be precisely computed and removed from MSL. One of the methods used for the study of physical response of a system to environmental effects in time domain is the “local response with weight function” or “impact response function” technique. The aforementioned function reveals the point-wise relation between the input and output of the physical system of interest, and in this way makes the point-wise modeling of the local variations of the system possible. In this study the weighted local response technique is used for SST computations in four tide gauge stations along the Persian Gulf, namely Shahid-Rajai Port, Kangan Port, Bushehr Port, Imam-Hasan Harbor, as well as the related meteorological stations. According to the numerical results, SST within the winter time in the studied stations varies between -82cm (in Bushehr Port) to +2cm (in Shahid-Rajai Port). The maximum SST value in Bushehr Port shows the reduction of the mean Persian Gulf level, while the minimum value of SST in Shahid-Rajai Port shows the rise of sea level due to SST in that area. This result is also in agreement with the geographical location of the two stations. Shahid-Rajai port being closer to the Oman Sea is dominantly affected by the topography of the Oman Sea and sea incoming currents to the Persian Gulf from the Oman Sea. Bushehr Port is farther away from the Oman Sea and as such is less affected by the Oman Sea currents. This finding is also reported in the previous studies over the region. Therefore, it can be concluded that SST computation using weighted local response technique is sufficienty accurate for the computation of SST and specially SST difference between the tide gauge stations.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21424_bc02e49aa67e0d106227ffead8682379.pdf
Studying the fluctuation of mixed layer height of Tehran, using MM5 modeling system
Farhang
Ahmadi Givi
author
Samaneh
Sabetghadam
author
Abbas Ali
Aliakbari Bidokhti
author
text
article
2009
per
Mixed layer is a part of the atmospheric boundary layer in which pollutants are uniformly distributed. It is sensitive to the Earth’s surface, controls the flow of heat and momentum between the surface and the free atmosphere, thus playing a key role in atmospheric circulation. Most of atmospheric pollution models require the height of the mixed layer as an input to determine the depth of atmosphere through which surface emitted pollutants are well mixed. Thus, the study of the depth variation of this layer is important in the spatial and temporal distribution of air pollution. This can be estimated from direct measurement and also from numerical forecasting models (such as MM5) with a proper boundary layer scheme.
In this research, first we study the variations of the depth of the daytime mixed layer for the city of Tehran for two months, August and February 2005 which are representative of warm and cold seasons, respectively. Next, the maximum and minimum depths of the mixed layer for each month are selected. Then the affecting variables concerning these maximum and minimum amounts, such as synoptic conditions, temperature advection, humidity, surface fluxes, vertical motions and vertical wind shears, are examined.
We attempt to compare the results calculated by means of MM5 with the same height derived by radiosonde. Three domains of MM5 are defined using 9, 3 and 1 km resolutions. The smallest domain is centered at the radiosonde position. We use simple-ice for the explicit moisture scheme, cloud radiation for the radiation scheme, and B-M scheme for the cumulus parameterization. Boundary layer processes are calculated using the Medium Range Forecast (MRF) scheme.
In general, the simulated potential temperature, mixed layer depth, and specific humidity by the numerical model are consistent with the variables measured by radiosonde. However, the model is not able to capture the fine structure of the mixed layer. The results display considerable seasonal variability in the mixed layer depth. For instance, the midday mixed layer depth is found to be nearly 3 km in summer for calm weather conditions, and is nearly twice as that of the wintertime. It is also seen that the monthly trend of mixed layer depth variations in the two months are close to those of the surface heat flux. It seems the fluctuations in the depth variations of this layer result mostly from temperature advection in summertime, while in wintertime, the midday depth is mostly affected by weather systems and wind shear rather than other physical processes.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21425_c1db124f3b51059d36d4bf8484255a59.pdf
Seasonal and daily variation of air pollutants and their relation to meteorological parameters
Zahra
Shariepour
مؤسسه ژئوفیزیک دانشگاه تهران، کارشناس هواشناسی
author
text
article
2009
per
In this paper, seasonal and diurnal variation of pollutants and the relation between meteorological parameters and the amount of pollutant concentrations is investigated. The data used were obtained from the Air Quality Department of the Municipality and from the synoptic station of the Institute of Geophysics. In this survey, the data used are from 2004 to 2007.
The result of survey for seasonal variation of pollutants showed that for CO, NO2 and PM-10, two maxima exist one of which occurs in summer and the other in winter, the maximum of SO2 is in winter and the maximum of O3 occurs in spring. The existence of maximum in winter may be from increasing consumption of fuels in thermal sources, besides meteorological conditions like increased air pressure, stability and temperature inversion. Maximum in summer may be from various factors like surface temperature inversion and decreased precipitation.
In October, often because of the reopening of schools and universities, and the consequent increased traffic, a temporary rise in the quantity of pollutants. The increased ozone production of photochemical reactions in spring and summer can be one of the effective factors for the existence of an ozone maximum in these seasons.
Increased dry air in summer can help to raise PM-10 concentration in this season.
The comparison of diurnal pattern of various pollutants in spring shows that all pollutants other than O3 have two maxima, one of which occurs in the early morning and the other late at night. But the pattern of O3 is different from other pollutants and its maximum occurs generally in the afternoon. Transport vehicles cause an increase in pollutants in early morning and at night. So, temperature inversion is effective in these maxima. Winter and summer CO diurnal pattern also shows morning and night maxima.
Photochemical reactions of ozone production, are effective in its maximum. In general, the height of mixing layer is decreased at nights and air pollutants are trapped under this layer, so that the concentration of pollutants is increased at nights. Also the katabatic wind has a tremendous effect on the increase of pollutants.
For the first six month period (from January till June) of 2007, the highest averages of concentrations of CO , NO2 , PM-10 and O3 pollutants, occurred at temperatures of more than 30?C but for SO2 the highest concentration was at less than 10?C . In this period, for O3 , NO2 and PM-10 pollutants the highest concentration is at relative humidity less than 40% and for SO2 and CO from 41% to 60%.
Multivariable regression statistical analysis between the concentration of ozone and NO2 pollutants with meteorological parameters like temperature and relative humidity for the first six months of 2007 showed that both parameters had effects on pollutant concentrations but temperature was more effective on ozone and relative humidity was more important for NO2 concentration.
In other words, although between O3 and NO2 pollutants and the temperature parameter, there is a positive correlation, between these pollutants and relative humidity there exists a negative relation.
The inversion of surface temperature (22 m height) in the early morning hours is one of the effective parameters in daily pollutant concentration and its effect is more important in summer months.
The investigation the effect of holidays on pollutant concentration, shows that in the stations like the Grand Bazaar Station where traffic is decreased on weekends and holidays in relation to other days, a decrease in CO pollutant is observed. In this case, the average decrease in CO pollutant is nearly 19 percent.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21426_83a43655d8261eb45479dbc8c46dd9bf.pdf
Longshore currents simulation using MIKE 21 numerical model
Case study: Kiashahr Zone
Mehdi
Esmaeili
دانشگاه دریانوردی و علوم دریایی چابهار، کارشناس ارشد
author
S. Ali
Azarmsa
دانشگاه تربیت مدرس، دانشیار
author
Ali
Karami Khaniki
مرکز تحقیقات حفاظت خاک و آبخیزداری
author
text
article
2009
per
INTRODUCTION: Determination of waves and the pattern of coastal currents is the first step in finding the effective physical factors on marine environments and coastal regions. Moreover, wave induced currents play important roles in the determination of geometry and shape of coasts. In this research, patterns of longshore currents are simulated for situations before and after construction of jetties on the mouth of the Kiashahr lagoon. Construction of jetties may lead to change in the pattern of coastal currents not only near the entrance of the lagoon, but also in the adjacent areas. Therefore, a precise study is necessary to understand and prevent the possible impact of the jetties on the study area. For this purpose, MIKE 21 software package was used to simulate patterns of longshore currents before and after construction of the jetties. The field measurements in the Kiashahr coastal area are also used for calibration of the model parameters. Besides, the results of this study can be used for other related research works on sediment transport, water quality, etc. in the study area.
Material and Methods: Kiashahr fishing harbor is located in the northwestern part of the Iranian coast of the Caspian Sea at geographical coordinates on the 39° 57? E and 37° 26? N. Kiashahr harbor and Kiashahr lagoon are situated on the east side of Sefid Rud river, which is the most important river in the southern part of the Caspian Sea (Figure 1).
The Model: The applied modeling system MIKE 21 consists of several separate modules. In this study, the hydrodynamic module (MIKE 21 HD) is used to calculate the water movements in the Kiashahr coastal area. MIKE 21 HD is the basic computational hydrodynamic module of the entire MIKE 21 system, providing the hydrodynamic basis for other MIKE 21 modules such as for Advection-Dispersion (AD), Particle tracking (PA) and Sediment Transport (ST, MT). HD module simulates the water level variations and flows in response to a variety of forcing functions in lakes, estuaries, bays and coastal areas. The water levels and flows are resolved on a rectangular grid covering the area of interest.
MIKE 21 HD includes formulations for the effects of; convective and cross momentum, bottom shear stress, wind shear stress at the surface, barometric pressure gradients, coriolis forces, momentum dispersion, wave-induced currents, sources and sinks (mass and momentum), evaporation, flooding and drying.
The equations for the conservation of mass and momentum (x and y directions) are integrated over depth to describe the flow and water level variations. The equations are solved by implicit finite difference techniques with the variables defined on a space staggered rectangular grid.
Run of the MODEL: The first step in the simulation of longshore currents is selection of the run extents in the hydrodynamic module (set up of the regional model). Dimension and extents of regional model depend on boundary situation and model boundary conditions. In addition, accuracy of available hydrographic maps is effective on determination of regional model extents. It is necessary to firstly run nearshore spectral waves module (NSW) and calculate the radiation stress data to use as input in the HD model. For each section (before and after construction of the jetties) 50 regional models in the Kiashahr marine area were set up to simulate littoral current velocities using the mud transport module (Table 1).
RESULTS: Figures 1 and 2 show the simulation results obtained for the representative cases before and after the construction of jetties. In these figures, vectors indicate direction and size of longshore currents.
Based on the model results, construction of jetties has not considerably influenced the general pattern of littoral currents in the Kiashahr Zone.
For the purpose of comparison, some stations are considered in the model area and variations in littoral current velocities are investigated for conditions of before and after the construction of jetties (figures 3 and 4).
The results presented in this study show that the currents due to easterly waves have more influence on the mouth of lagoon. In addition, comparison of patterns for both situations indicated that after the construction of jetties, current speed around the lagoon entrance (Stations P6, P8 and P9) was reduced about 35 percent so that the harbor entrance has become a calm place.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21427_2217d3849a020fab3edebd22cdf533dd.pdf
Sink-hole modeling at a power plant site using microgravity data
Vahid
Ebrahimzadeh Ardestani
مؤسسه ژئوفیزیک دانشگاه تهران، دانشیار
author
text
article
2009
per
A microgravity survey was conducted for detecting the sink-holes at site of a power plant.
Pits, man-made tunnels and canals were considered as topographical effects and were corrected. To show the capability of the method two sites in a power plant have been surveyed for existing areas which can be affected by sink-holes overnight.
Ground shakes due to the running facilities were also preventing us from taking a calm measurement.
Despite all unwanted factors at site, we could delineate the sink holes quite accurately. The depth of and the shape of these anomalies have been modeled by 3-D inversion of micro-gravity data.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21428_8637291daf84f73cbae77fc02987d468.pdf
Combined analytic signal and Euler method (AN-EUL) for depth estimation of gravity anomalies
Vahid
Ebrahimzade Ardestani
مؤسسه ژئوفیزیک دانشگاه تهران، دانشیار
author
text
article
2009
per
The method expressed by Salem and Ravat. (2003) for depth estimation of magnetic sources is used on gravity anomalies for the first time.
The depth of some rectangular prisms as synthetic models are estimated through the method. The gravity effect of these models is also considered with a relatively high value of random noise. A field example is also included and the depth of the main anomaly has been estimated using this method.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21429_c2682f33481e077cefca3c868c52b570.pdf
Depth and shape factor determination of gravity anomalies by linearized least-squares
vahid
Ebrahimzade Ardestani
مؤسسه ژئوفیزیک دانشگاه تهران، دانشیار
author
text
article
2009
per
A new method derived by Salem et al. (2004) for interpretation of gravity and magnetic anomalies is used to determine the depth and shape factor of the gravity anomalies.
The depth and shape factor of some rectangular prisms as synthetic models are estimated using the method. The gravity effects of the models are contaminated with some random noise and then the parameters of the models are extracted through the erroneous data.
A field example is interpreted and the depth and shape factor of the main anomaly has also been estimated through the method.
Journal of the Earth and Space Physics
Institute of Geophysics, University of Tehran
2538-371X
35
v.
2
no.
2009
https://jesphys.ut.ac.ir/article_21430_87da0f1cdfd370c83715f403b8675c6c.pdf