Geodetic Instruments Research Articles

A New Method for In-situ Non-contact Roughness Measurement of Large Rock Fracture Surfaces

This paper presents a new method for in-situ non-contact measurements of fracture roughness by using a total station (TS). The TS is a non-reflector geodetic instrument usually used for measuring control points in surveying and mapping. By using a special-developed program, the TS can be used as a point-sensor laser scanner to scan a defined area of the fracture surface automatically, in field or in laboratory, at a distance away from the target surface. A large fracture surface can be automatically scanned with a constant interval of the sampling points, both within a defined area or along a cross-section of the exposed rock face. To quantify fracture roughness at different scales and obtain different densities of the scanned points, the point interval can be selected with the minimum interval of 1 mm. A local Cartesian co-ordinate system needs to be established first by the TS in front of the target rock face to define the true North or link the measurements to a known spatial co-ordinate system for both quantitative and spatial analysis of fracture roughness. To validate the method, fracture roughness data recorded with a non-reflector TS was compared with the data captured by a high-accuracy 3D-laser scanner. Results of this study revealed that both primary roughness and waviness of fracture surfaces can be quantified by the TS in the same accuracy level as that of the high accuracy laser scanner. Roughness of a natural fracture surface can be sampled without physical contact in a maximum distance of tens of meters from the rock faces.

Sudden aseismic fault slip on the south flank of Kilauea volcano.

One of the greatest hazards associated with oceanic volcanoes is not volcanic in nature, but lies with the potential for catastrophic flank failure. Such flank failure can result in devastating tsunamis and threaten not only the immediate vicinity, but coastal cities along the entire rim of an ocean basin. Kilauea volcano on the island of Hawaii, USA, is a potential source of such flank failures and has therefore been monitored by a network of continuously recording geodetic instruments, including global positioning system (GPS) receivers, tilt meters and strain meters. Here we report that, in early November 2000, this network recorded transient southeastward displacements, which we interpret as an episode of aseismic fault slip. The duration of the event was about 36 hours, it had an equivalent moment magnitude of 5.7 and a maximum slip velocity of about 6[?]cm per day. Inversion of the GPS data reveals a shallow-dipping thrust fault at a depth of 4.5[?]km that we interpret as the down-dip extension of the Hilina Pali--Holei Pali normal fault system. This demonstrates that continuously recording geodetic networks can detect accelerating slip, potentially leading to warnings of volcanic flank collapse.

IGS stations: station and regional issues

This paper presents an overview of selected IGS station equipment and regional issues and was presented as the position paper for the session ‘Regional operations and equipment issues’. Regional issues include IGS network densification of areas which are sparsely populated with IGS stations. Station specific issues include GPS and peripheral equipment, footprints, space geodetic and geophysical instrument collocation, data latency, integrity monitoring and station installation procedures. There are several issues pertinent to equipment and regional issues which are in the process of being addressed by various agencies, some issues such as global densification do however require more effort.

Detection of a crack‐like conduit beneath the active crater at Aso Volcano Japan

To constrain the source of long period tremors (LPTs), we deployed a very dense broadband seismic network consisting of totally twenty‐four stations around the active crater of Aso volcano in Kyushu, Japan. The spatial variation of the observed signal amplitudes reveals that the source of LPTs consists of an isotropic expansion (contraction) and an inflation (deflation) of an inclined tensile crack with a strike almost parallel to the chain of craters. The detected crack has a dimension of 1 km and its center is located a few hundred meters southwest of the active crater, at a depth of about 1.8 km. The extension of the crack plane meets the crater chain including the active fumarole at the surface, suggesting that the crack has played an important role in transporting gasses and/or lava to the craters from below. This work also demonstrates a powerful usage of broadband seismometers as geodetic instruments to constrain subsurface structures at active volcanoes.

Remarkable tilt–strain anomalies preceding two seismic events in Friuli (NE Italy): their interpretation as precursors

Crustal deformation data collected in the Friuli seismic area (NE Italy) through the employment of geodetic instrumentation are analysed to evaluate observed signals considered as preseismic. Once the disturbing action of atmospherical/hydrological factors on local crustal deformation data has been considered in previously published studies, two middle-term precursors (one tilt and one areal strain) are presented, as being the strongest and more evident signals recorded in the area after the 1976 destructive seismic events. An effort is also performed in their interpretation and modelling. Evaluations on the basis of micro-cracking of the source region and aseismic fault creep are done. Modelling based on trivial rheological models furnishes crustal viscosity values in agreement with the values obtained in the analysis of the silent earthquakes recorded in the same area before the 1976–77 destructive seismic events. We put forward the hypothesis that for both the presumably preseismic signals the viscosity plays an important role, although in one case slow dislocations could also have occurred. The two strong possible preseismic signals here considered support the hypothesis proposed by some authors that evident and reliable precursory signals can be detected only within a distance of 2–3 times the dimensions of the source area.

Estimating the hydrologic induced signal in geodetic measurements with predictive filtering methods

The high precision achieved with continuous geodetic instruments makes it necessary to take ambient factors into account. Among these, one of the most disturbing is the hydrologic agent. After giving a characterization of the induced signals in the specific case of subsurface tilt and extensometric measurements, the techniques of predictive filtering are shown to solve the problem of modeling the induced signals. The results obtained here may be applied also to other continuous geodetic and gravity measurements.

TEST RANGE FOR CALIBRATION AND CLASSIFICATION OF GEODETIC INSTRUMENTS

The test range of Escola Politécnica da Universidade de São Puaulo (EPUSP) at the campus of the University of São Paulo (USP) was constructed to calibrate electronic distancers (EDM) on a multipillar baseline and also to classify theodolites and levels according to the Brazilian Standard Norm NBR 13 133/1994. This paper shows in detail the different approaches and methods used in field observations, adjustments and results. The test range provides test and calibration facilities for manufacturers, researchers and users of geodetic instruments.

Observations at Costa Rican volcano offer clues to causes of eruptions

Recent measurements of ground deformation at an active volcano show great promise for elucidating the processes that lead to volcanic eruptions. A long‐term effort to continuously monitor ground deformation over a very wide bandwidth using state‐of‐the‐art geodetic, seismic, and acoustic instruments at Arenal Volcano in Costa Rica is producing high‐quality recordings of harmonic tremor and explosive events and offers an exciting opportunity to explore possible lunar periodicities in volcanic eruptivity.

Use of the satellite geodesy method in studying movements of the slopes of the Zagorsk pumped-storage station

research center carried out experimental measurements in the horizontal control network of the PSS with the use of the satellite geodesy method to evaluate the effectiveness of its use on the object. The characteristics of the network and instruments used, results of experimental measurements as well as a comparison of the measurement results by new and traditional methods are given below. A schematic diagram of the existing horizontal control network of the Zagorsk PSS is shown in Fig. 1. The coordinates O f points on the slope were determined from the control network by various methods. The points of the network were stabilized by pipe-type marks (depth of placement 2.5 m). The pipe of the mark projects 1.2 m above the surface, a disk is welded to its top for placement and forced (mechanical) centering of the geodetic instruments and equipment. The centering error is about 0.1-0.2 mm. The control network is linear-angular. The sides of he network were measured in the latest cycles by a Geodimeter 14A, the angles by a type T2 theodolite with nine rounds. The standard deviations (SDs) of measuring the lengths of the sides and angles were 2-3 nun and 1.5". The network was adjusted as free, and the "center of gravity of the network" with coordinates X o = ~Xi/n , Yo = ~Yi/n, where X i and Yi are the coordinates of the network points and n is their number, was taken as the starting point. In all cycles X 0 and Y0 are the same. According to the adjustment results, the SDs of the abscissas and ordinates of the points were within 0.2-1 mm, and the errors of the position of the points did not exceed 1.1 mm. The differences of the coordinates of the points between cycles were within the accuracy of determining them.

First steps to expert intelligence in Geodetic Instruments

First steps to expert intelligence in Geodetic Instruments

Centimeter repeatability of the VLBI estimates of European baselines

In the last three years, the European Geodetic Very Long Baseline Interferometry (VLBI) Network has grown to a total of six fixed antennas placed in Germany, Italy, Spain and Sweden, all equipped with the standard geodetic VLBI instrumentation and data recording systems. During this period of time, several experiments have been carried out using this interferometer providing data of very high quality due to the excellent sensitivity and performance of the European stations. The purpose of this paper is to study the consistency of the VLBI geodetic results on the European baselines with respect to the different degrees of freedom in the analysis procedure. In order to complete this study we have made use of both real and simulated data sets, two different software packages (OCCAM 3.0 and CALC 7.4/SOLVE) and a variety of strategies in the data analysis. The results we have obtained show that the repeatability of the VLBI estimates of the baseline lengths in the European network is better than one centimeter, independent of the different analysis methods, and is consistent with the formal error levels expected from the data analysis. This consistency should be enough to produce geophysically significant information in Europe from VLBI data within a relatively short time span.

Late Holocene movement along the San Andreas Fault at Melendy Ranch: Implications for the distribution of fault slip in central California

An alluvial deposit of the San Benito River at Melendy Ranch, which is located along the creeping segment of the San Andreas fault in central California, records an 800‐year‐long average slip rate of 22−4+6 mm/yr. The rate is calculated from one radiocarbon age and two measures of displacement and is based on various sedimentologic and stratigraphic data. Numerous other radiocarbon ages were determined for detrital charcoal from the alluvium at Melendy Ranch. These radiocarbon ages appear to be at variance with the age of the alluvium on the basis of sedimentologic and stratigraphic data. The 22 mm/yr long‐term rate is similar to the 20–23 mm/yr range of slip rates that are recorded by geodetic instruments at Melendy Ranch and a 22 mm/yr slip rate recorded by an offset corral fence built in 1945. This suggests that the historic rate of movement along the San Andreas fault at Melendy Ranch is near its 800‐year average. The long‐term slip rate of about 22 mm/yr at Melendy Ranch is 12−5+7 mm/yr less than the long‐term rate found along the San Andreas fault south of the creeping segment, and it is greater than the minimum long‐term rate of about 12 mm/yr found along the fault north of the creeping segment on the San Francisco Peninsula. Thus the long‐term slip‐rate data suggest a ∼20 mm/yr northwestward decrease in slip rate along the San Andreas fault. The northwestward decrease in long‐term slip rate is attributed to a two‐part transfer of slip, south of Hollister, from the San Andreas fault to the Paicines and Calaveras faults. If the Paicines and Calaveras faults south of Hollister have a combined long‐term slip rate of about ∼20 mm/yr, then a similar rate may also represent slip across the Calaveras and Hayward faults north of Hollister.

Scientific and technical progress in engineering-geodetic surveys

This paper reviews the progress made in the Soviet Union in geodetic survey methodology, instrumentation, and data processing facilities with regard to siting future hydroelectric, pumped storage, and nuclear power plants and to assessing the geologic behavior of sites already in existence for sings of deformation or settling or tectonic or seismic activity.

INSTABILITY OF PRECISE GEODETIC INSTRUMENTS CAUSED BY GROUND VIBRATIONS

AbstractThe work reported here is a continuation of investigations carried out for determining the influence of vibrations on the accuracy of geodetic measurements. The purpose of this study is to determine the influence of ground vibrations on different groups of precise geodetic instruments.

INFLUENCE OF VIBRATIONS ON THE STABILITY OF GEODETIC SIGNALS AND INSTRUMENTS

Within the framework of present publications propagation and transference of vibrations by the ground from their source to geodetic instruments and marks were analysed and considered. To find confirmation for the theoretical model described in the foregoing, vibrations of the precise geodetic instruments were measured and analysed.

INFLUENCE OF VIBRATIONS ON THE STABILITY OF GEODETIC SIGNALS AND INSTRUMENTS

Within the framework of present publications propagation and transference of vibrations by the ground from their source to geodetic instruments and marks were analysed and considered. To find confirmation for the theoretical model described in the foregoing, vibrations of the precise geodetic instruments were measured and analysed.

STATINIŲ DEFORMACIJŲ, KILUSIŲ DĖL VIBRACIJOS IR PASTOVAUS ŠALDYMO, TYRIMAI

Click to increase image sizeClick to decrease image size Резюме Описываются результаты исследования деформаций строений. вызванных производственными процессами. Для примера подобраны компрессорные крупного химического завода и камеры городского распределительного холодильника. Делаются выводы, что каждое исследование деформаций, вызванных деятельностью человека, является своеобразным, для наблюдений за ними необходимо составлять индивидуальную программу с обязательной ее корректировкой в течение исследования. Часто эти деформации со временем не затухают, а возрастают, они значительно опаснее статистических деформаций. поэтому необходимо вести наблюдения за ними продолжительное время. Summary The paper deals with the study of structure deformations caused by engineering production. As the typical examples serve a compressor house of a huge chemical plant and the chambers of the distributor refrigerator. The data concerning the results of the investigations, the peculiarities of the technique of observations and the effect of control on the applied geodetic instruments (Koni 007) are presented in the paper. The conclusions are drawn that every recearch on the structure deformations caused by man's activity is original for it requires a special program to be worked out for it. The program should be adjusted during the whole research process. The deformations of such type seldom die out. They have actendency to increase with time, they are more dangerous than static deformations as they are to be supervised for a long time. The study of such deformations have an influence on the geodetic instruments in usage.

The present state and prospects of development of high-precision geodetic methods for studying recent crustal movements

The principal task in studying recent crustal movements at the present stage, along with elaborating theoretical concepts, continues to be that of accumulating quantitative information about as many parameters as possible which characterize the spatial, temporal and energetic spectra of these movements. The author deals with some questions of improving the geodetic methods and instruments and makes an attempt to show the accuracy with which the speed of recent horizontal and vertical crustal movements can be measured today and in the future.

Geodetic instrumentation

Although significant advances have occurred in geodetic instrumentation during the past 20 years, especially with respect to converted inertial navigation systems and satellite related instrumentation, they did not result from systematically following some well organized development plan. Instead, these advances have originated for a variety of reasons—the availability of new technologies either directly or indirectly relatable to instrumentation, accuracy requirements stated in support of particular tasks, and improvements or developments accomplished or initiated by individual scientists, commercial instrument concerns, or field users. Developments or advances occurring during 1975–1978 are recorded herein.

Effects of Ground Motions on Amplitude Interferometry

AbstractSome examples are given of types of ground motion which hs.ve been observed with seismic and geodetic instruments. In general, away from sources of man-made noise, the amplitudes of ground strains and tilts in the microseism band with periods of a few seconds normally are of the order of a few times 10-10. Strain and tilt tides give amplitudes of a few times 10-8, and long term average strain and tilt rates at relatively good sites may be roughly 10-7/yr. Superposed on such relatively long wavelength motions can be larger local pier motions, which are likely to be irregular. However, very high ground stability has been demonstrated at a few sites The limitations of ground motions on long term amplitude interferometer stability are serious if applications such as earth rotation and polar motion measurements are considered, but at shorter periods the environmental problems will be almost completely atmospheric.