Showing papers by "Geophysical Survey published in 2006"

NDE methods for quality assurance of new pavement thickness

Abstract: Accurate measurement of pavement thickness is an essential aspect of the quality assurance of new pavement construction. Current coring methods are time consuming and provide a very limited representation of the overall pavement structure. The objective of the work described in this paper has been to demonstrate the use of non-destructive evaluation (NDE) methods for rapidly determining the average pavement thickness on a newly constructed section to within 2.5 mm of the true value, without extensive reliance on cores. The effort has considered ground penetrating radar (GPR) and impact echo methods applied to both asphalt and concrete pavement, and has included laboratory and field-testing, with field correlations based on 172 cores. The results show that the 2.5 mm accuracy objective can be met for asphalt pavement, but that accuracy on concrete is limited to 4 mm. The paper describes the techniques that were evaluated, the testing that was conducted, and the results of correlation with core data.

Measurement quality estimation of proton-precession magnetometers

Abstract: A method for calculating quality estimation of the magnetic field value measured by proton-precession magnetometers from data of single measurement is presented. This method is appropriate for frequency measurement algorithms which process time-series of signal’s zero crossing. Expressions for measurement error estimation are obtained taking into account signal decay and correlated noise. Presented formulas allow a result reliability to be estimated immediately in single measurement and give an opportunity for complex control of a device performance. Correlation and relaxation corrections are given. It was experimentally tested that the standard deviation of measurements is in a good qualitative agreement with presented error estimation.

High-frequency seismic noise: Results of investigation in Kamchatka

Abstract: The investigation of seismic noise in Kamchatka is carried out for the control of the medium stress condition and search of the strong earthquakes precursors. The main directions of this research are modulation of high-frequency seismic noise (HFSN, frequency range of the first tens of Hz, amplitudes about 10−9–10−12 m) by the Earth tides and temporal variations of HFSN parameters connected with the strong earthquake preparation. For reception of the statistically significant characteristics of HFSN and tides connection it was necessary to carry out long-term HFSN observations in points free from anthropogenous influence as far as possible. The station of HFSN observation was organized in the settlement Nachiky. The sensor is a narrow-band (Q = 100) piezoelectric seismometer, tuned to frequency 30 Hz. Signal envelope is recorded and analyzed. The continuous HFSN registration was begun in 1990 and proceeds till now. In 2000 the second station was established in the complex geophysical observatory “Karymshina”. The HFSN sensor is set up in the borehole at the depth of 30 m. The research of HFSN structure gave the opportunity to allocate HFSN components connected with the Earth tides. Besides it was revealed that the tidal response is not stable in time: the intervals of the tidal component existence are replaced by intervals of its absence, correlation between tide and HFSN varies in time, while tides have constant parameters. We propose a hypothesis about the connection of variations of the tidal components in HFSN data with the tectonic conditions in region, and consequently, about an opportunity to use this phenomenon for the prediction of strong earthquakes. The phase of the HFSN component connected with a tidal wave O1 (T = 25.8 h) was chosen as a parameter. The choice of wave O1 is connected with its greatest hindrance-immunity. It was shown that the stabilization of this phase is observed before earthquakes with M > 6.0, occurred at distances up to 250 km from the HFSN registration point, within time from several weeks to several months. Since 1996 such an analysis of the HFSN response to tides is conducted in an operative mode, and only in 1 case out of 19 the large earthquake precursor was not shown in any way.

Object Recognition of Ground Penetrating Radar in Karst Regions Using Wavelet Energy Spectral Analysis

Abstract: The frequency and amplitude characteristics derived from the Ground Penetrating Radar (GPR) data have been widely applied to object recognition in karst areas, but still meet some limitations. Here we present a new method using wavelet energy spectral analysis. First we analyze the GPR signals of typical samples in karst areas and obtain their wavelet energy spectra, which consist of the energy eigenvectors on different scales and frequency bands. Then the object recognition is achieved by comparing the characteristic energy spectra with those of studied object. Both the data analysis and experiments demonstrate that the wavelet energy spectrum can directly show characteristics of object signals, which is very effective for the object recognition in karst regions from the GPR survey.

Spectral characteristics of atmospheric pressure and electric field variations under severe weather conditions at high latitudes

Abstract: . The time-dependent relationships between atmospheric parameters (electric field, positive and negative conductivity, variations of atmospheric pressure) and different meteorological phenomena (rain, fogs, snowstorms, thunderstorms) were investigated through spectral analysis. These parameters were measured with help of a high-latitude computer-aided complex installed at Apatity (66.5 N, 33.4 E). The complex consists of three spaced microbarographs for measurements of atmospheric pressure variations in the range of periods from 1 s to 40 min, an instrument measuring the vertical component of the electric field, and instrument used for measurements of air conductivity and surface ozone. A computer-aided data-gathering system makes it possible to obtain information in the frequency range between 1 and 0.0001 Hz. The time-dependent frequency analysis showed that the spectral characteristics of both electric field and atmospheric pressure variations changed synchronously during severe weather conditions.

Geological Evidences of the Deformation in Central-Southern Ningxia in the Miocene and Its Significance

Abstract: By analyzing the regional distribution of unconformity in Cenozoic strata and their sedimentary characteristics we found that there were at least two tectonic events affecting central-southern Ningxia during the Miocene, one in the Early Miocene, the other in the late Middle Miocene, and the later one was much stronger and more widespread than the former one. The former one was found to the west of the Liupan Mountain, and the later mainly occurred along the Chahanbulage-Sanguankou-Qingtongxia-Guyuan (Cha-Gu) fault. Most the Hongliugou Formation in central-northern Ningxia was deposited under stronger tectonism in the Miocene. The tectonic event in the early Miocene mainly distributed to the west of the Liupan Mountain including eastern Gansu, and this event resulted in the deformation of the Qingshuiying Formation and the unconformity between the Hongliugou Formation and Qingshuiying Formation. Because most of these phenomena were distributed along the Haiyuan fault and adjacent areas, we conjecture that the Haiyuan fault may be active in the early Miocene. And the event in late Middle Miocene had shown its existence in the following aspects, in the west of the southern Helan Mountain the thrusting taking place in the late Middle Miocene has been found, thick syntectonic sediments, Hongliugou Formation was deposited, the unconformity between the Hongliugou Formation and Qingshuiying Formation because of the tectonism in late Middle Miocene along the Cha-Gu fault was also found, the Hongliugou Formation in these areas also deposited at the same time, which means that during that time the deformation front of the Qinghai-Tibetan plateau had extended to the Cha-Gu fault, i.e. the western margin of the Ordos basin, the early Cenozoic basin was dismembered in this event; and at the same time the Hongliugou Formation in the basin became coarser and coarser upwards which also means that in the late Middle Miocene one stronger tectonic event had affected this region. This event led to the uplifting of the Xiang Mountain, which dismembered the former basin to small piggy-back basins. Undergoing these two tectonic events, central-southern Ningxia had been incorporated into the thrust wedge of the northeastern Qinghai-Tibetan plateau, and the reason for this thrust wedge extending to the northeast may be the remarkable uplifting of the northern part of Plateau at the same time which resulted in the taper angle of the wedge over the critical value and made it spread forwards. The Cha-Gu fault was once similar to the present Haiyuan fault as the deformation front, and the development of the whole of northeastern plateau was not forward-breaking, but expended with out-of-sequence. The above phenomena are not consistent with the viewpoint of former workers that the deformation of Cenozoic strata in Ningxia occurred since the end of the Pliocene.

Discussion on the Tectonic Setting of Deposition of the Eocene Sikouzi Formation in Ningxia Region

Abstract: As the first sediment in Cenozoic time in Ningxia region, the Eocene Sikouzi Formation has special tectonic meaning, however, its development has not been interpreted satisfactorily yet. From the point of deposition scope and more radical change of sedimentary facies, the Sikouzi Formation occurred abruptly. By the means of facies and structural analysis, the authors think that the Sikouzi Formation was deposited on the forebulge facing to the Corridor Nan Shan which resulted in the development of one foreland basin 30~40 Ma ago, the forebulge unit of this foreland basin was located along the western margin of Ordos Basin and Xiangshan area, the back-bulge unit lay to the east of western margin of Ordos Basin. Because of flexing, many normal faults dipping to the orogen came into being on the forebulge, it was these normal faults that controlled the distribution of Sikouzi Formation which was deposited rapidly and formed a serial of alluvial fans around forebulge, the provenance of it was the uplifts along the western margin of Ordos Basin and Xiangshan area, etc.

Application potential of DMC satellite data in geosciences

Abstract: This paper focuses on remote sensing information extraction in geological environment survey and disaster evaluation. DMC satellite multispectral data of tsunami area in Sumatran island and Namucuo area in Tibet is selected as the data source. After data processing and synthesis analysis such as fine geometric correction, image radiation analysis, information enhancement, information extraction, geological interpretation etc., and with the support of the known remote sensing and geological data, the information of Quaternary geology, environment, disaster, desertification in Namucuo Lake and surrounding area is extracted. With regard to tsunami area in Sumatran island, obvious linear and ringed textures in the image are extracted, mapped and analyzed from chromatic aberration of vegetation and texture information, and its geological meaning is interpreted. Northwest fault is the main fault, the smaller one is the northeast fault which is perpendicular to the main fault. Based on that, we have initially analyzed the fracture distribution characters that probably control or induce geologic disasters of the region, and we have also predicted three regions where geological disasters such as debris flow, landslip, landslide etc easily take place and two probable regions where volcanic activities happen. Using DMC satellite data of Namucuo Lake and its surrounding area in Tibet we can recognize lots of information such as lake-face stratum of the Quaternary, bare bedrock, linear feature, two-level and three-level water system, glacier distribution. Through the comparison and analysis of two-period image, we have found four debris flow areas caused by snow melting in the surrounding region of Bingna, Bencuoduo, and Qinglongxiang. In the aspect of land desertification, through image classification, we can extract remote sensing information such as bare ground with grit, meadow, wetland, desertification land (severe, moderate and slight) and alkaline land (moderate and slight) etc. in Namucuo Lake region and its surrounding region. Geological disaster evaluation using DMC satellite data indicates that it not only have huge application potential for disaster monitoring, but also have important application value for geologic environment monitoring.

Gridding of Potential Field Data With Inverse Interpolation

Abstract: Gridding of irregularly distributed potential field data is one of the first and most crucial steps in data analysis. This paper brings forward to realize the gridding of potential field data by using inverse interpolation based on the preconditioning conjugate-gradient iterative algorithm. The gridding method adopts Gaussian weighted coefficients as the interpolation operator, Laplacian operator as the smooth filter, and the inverse of the smooth filter as the preconditioning operator. Experimental results on the synthetic model and the raw aeromagnetic data show that the method is suitable for the features of geophysical potential field, and is a computationally efficient and robust 2-D method with high accuracy and perfect effects.