Geodetic Deformation Analysis

This study investigates in detail the deformation events that
have affected the sedimentary successions forming the substrateof Mt.  Etna volcano (Italy). Based on the geometric
reconstruction of a buried sedimentary marker, we have been
able to identify and quantify the effects of three different
mechanisms of deformation that have affected the area in
the last 600 ka. Numerical results from Finite Element
Method (FEM) applied to model viscoelastic deformation suggest
the occurrence of a crustal doming process originating
at the mantle-crust transition (~16 km). We propose that the
source of deformation is related to the diapiric uprise of
hydrothermal material originating in altered ocean-like crust
and its emplacement at a shallower level in the crust. This
process has great relevance in the volcanic system and should
be considered for the full assessment of its origin and evolution.

Correct interpretation of surface stresses and deformation or displacement during volcanotectonic episodes is of fundamental importance for hazard assessment and dyke-path forecasting. Here we present new general numerical models on the local stresses induced by arrested dykes. In the models, the crustal segments hosting the dyke vary greatly in mechanical properties, from uniform or non-layered (elastic half-spaces) to highly anisotropic (layers with strong contrast in Young's modulus). The shallow parts of active volcanoes and volcanic zones are normally highly anisotropic and some with open contacts. The numerical results show that, for a given surface deformation, non-layered (half-space) models underestimate the dyke overpressure/thickness needed and overestimate the likely depth to the tip of the dyke. Also, as the mechanical contrast between the layers increases, so does the stress dissipation and associated reduction in surface stresses (and associated fracturing). In the absence of open contacts, the distance between the two dyke-induced tensile and shear stress peaks (and fractures, if any) at the surface is roughly twice the depth to the tip of the dyke. The width of a graben, if it forms, should therefore be roughly twice the depth to the tip of the associated arrested dyke. When applied to the 2009 episode at Harrat Lunayyir, the main results are as follows. The entire 3-7 km wide fracture zone/graben formed during the episode is far too wide to have been generated by induced stresses of a single, arrested dyke. The eastern part of the zone/graben may have been generated by the inferred, arrested dyke, but the western zone primarily by regional extensional loading. The dyke tip was arrested at only a few hundred metres below the surface, the estimated thickness of the uppermost part of the dyke being between about 6 and 12 m. For the inferred dyke length (strike dimension) of about 14 km, this yields a dyke length/thickness ratio between 2400 and 1200, similar to commonly measured ratios of regional dykes in the field.

Continuous and campaign-style Global Positioning System (GPS) measurements provide new constraints on the first-order current deformation pattern of the northern Cordillera of NW Canada and eastern Alaska. The Yakutat block is currently colliding with North America in the corner of the Gulf of Alaska. Our data infer that relative Yakutat-North America motion is accommodated across the eastern boundary by right-lateral motion (˜40 mm/a), mainly on the Fairweather fault, and minor shortening (˜6 mm/a). To the north, collision is taken up by shortening (˜31 mm/a) mainly on the Chugach-St. Elias fault system, with westward extrusion and possible counterclockwise rotation of the Yakutat block and Alaskan fore arc facilitated by ˜23 mm/a right-lateral motion that is shared by several faults. The seismicity pattern indicates that plate boundary deformation is far reaching, producing strain throughout eastern Alaska, Yukon, and western Northwest Territories. Our GPS data confirm the transfer of strain from the Yakutat collision zone and enable the extent of plate boundary deformation to be mapped, thereby defining the western edge of "stable" North America. GPS sites in SW Yukon show motion of 3-10 mm/a to the NE, confirming that strain is transferred at least 400 km from the Yakutat collision. Continued transfer north toward the Mackenzie Delta and NE to the Mackenzie Mountains, indicated by current seismicity, is not yet well resolved by the campaign GPS data, which are hampered by coseismic and postseismic effects of the 2002 Mw 7.9 earthquake on the Denali fault in eastern Alaska.

SUMMARY This paper presents some first results of a project aimed to access the feasibility of monitoring deformations of large concrete dams by terrestrial laser scanning. Case study of Studena Dam in Bulgaria is described. A large number of retro-reflecting targets have been positioned and measured by a total station in the local datum. Moreover, targets are measured also in captured scans. They are placed in the surroundings as ground control point. Two measurement campaigns are accomplished so far: the second one after earthquake in Pernik on 22.05.2012. Reported analyses are focused on two main problems: the first one is the accuracy and the stability of georeferencing, which is fundamental to make comparisons between different multi-temporal scans; the second one is the computation of deformation based on the acquired point-clouds. Moreover, some notes about a method to compute the accuracy of surface points which have been measured by terrestrial laser scanning are reported.

РЕЗЮМЕ
В статията са представени първите резултати по проект изследващ възможността за използване на наземно лазерно сканиране за мониторинг на деформации на големи бетонни язовирни стени. Разглежда се приложението на метода за язовир Студена. Контролни точки са стабилизирани извън деформационната област на обекта и са измерени с тотална станция в локална координатна система. Точките също така са сканирани за трансформиране на измерванията с лазерния скенер в локалната координатна система. Извършени са два цикъла измервания като вторият е след земетресението в гр. Перник на 22.05.2015 г. изложения анализ е фокусиран върху два основни проблема: първият е точността и стабилността на геореферирането, който е основен при сравнението на данни от различни епохи, а вторият е изчислението на деформациите при сравнението на облаци от точки.

The image based modeling finds use in applications where it is necessary to reconstruct the 3D surface of the observed object with a high level of detail. Previous experiments show relatively high variability of the results depending on the camera type used, the processing software, or the process evaluation. The authors tested the method of SFM (Structure from Motion) to determine the stability of gabion walls. The results of photogrammetric measurements were compared to precise geodetic point measurements.

The Puli Basin, located between the Western Foothills and the Hsüehshan Range is the largest basin in the active orogeny in central Taiwan. South to the Puli Basin, a series of small basins spread along the NNE direction. Various tectonic models have been proposed in previous studies to interpret the formation of the Puli Basin. In this study, we aim to measure the deformation and to understand the tectonics of Puli Basin by the method of satellite remote sensing and field observation. We applied the Persistent Scatterer Interferometric SAR technique to monitor the surface deformation. Our result shows a relative lower LOS velocity in Puli Basin, which implies the change of depth of the subsurface basal detachment. A steep ramp along the detachment is proposed for the grown structure underneath the Puli Basin in this study. In order to interpret the mechanism of surface deformation in central Taiwan, we implement several forward models based on previous researches and our interferometric results and then compare our observations with accurate GPS and precise leveling data. These results can be compared with our field observations and with the recent seismicity data (20130327 and 20130602) to examine the activity and geometry of faults of this area, where a conjugate fault system below the basins was suggested. Due to the lack of evidence, the relationship between the conjugate system and the basin subsidence mechanism is hard to determine but may be the key to understand the tectonic activity in central Taiwan.

Ageing earthfill dams become vulnerable to weather phenomena such as rainfall and flooding, with severe consequences, economic and life threatening, to the communities living downstream. A better understanding of their long-term behaviour and the factors affecting it, is crucial. A unique data set was used, consisting of the crest settlements of an earthfill, central clay core dam, the Pournari I dam in Greece, the daily reservoir level fluctuations and rainfall height values at the dam site between 1981 and 2015. The dam is 107 m high and its construction was completed in 1981. In previous studies the settlements of this dam, including rates, were found to be within limits and compliant with empirical relationships derived for dams of this type. In this work we remove the effect of primary consolidation and creep from the settlements and attempt to study the relationship between the residuals and rainfall. We find that consolidation was completed within 4 years since the end of construction (by 1985) and residuals of all points on the crest appear to follow the same evolution pattern. While no direct relationship could be established between the actual settlement observations and the rainfall, residuals seem to have maximum correlation with the cumulative rainfall height over a period of two months before the settlement measurement epoch. Our findings most likely represent a threshold value of rainfall above which the dam seems to be responding rather than a time duration over which rainfall plays an important role to the settlements of the dam.

One of the most crucial issues in engineering of structure and investigating ground deformation is deformation monitoring. The only thing which is strongly required is to create microgeodesy networks. An essential issue in microgeodesy networks is detecting unstable points of network. L1-Norm minimization and the global congruency can be noted as one of the classical methods for identifying network unstable points. In all previously conducted studies regarding this issue, results distinctly demonstrates that when displacement point vector is small, the number of points which have really displaced is more than that of true detection of displaced points using common deformation analysis ways. The probable reason for that can refer to spreading nature of the least squares estimation. Considering the results of recent studies in the detecting the network unstable points, to tackle the limitation the idea of subnetwork analysis is offered. In this case, some subnetworks including a subject point and the other source points appeared from dividing the deformation monitoring network. According to the unstable points, subnetworks will be there. This method will enable us to investigate the stable and unstable points. Having divided whole network to subnetworks, each network would be adjusted and unstable points of it would be detected. So, unstable points and their relations are cutoff and spreading effect of the least squares is fallen. This paper is on effort to evaluate the method in a simulated and a real network. The results prove that in a better and correct detection of unstable point can be successfully achieved by using subnetwork analysis compared to global congruency test all stimulates states proved the 35% of improvement on average. One percent of improvement in the results of subnetwork method to L1-Norm minimization cannot be acceptable. The algorithms of detecting unstable points in common methods and the method of analyzing subnetwork were conducted on a real network and the results are in line with simulated network results.

The sensitivity analysis of geodetic monitoring networks is realized mainly to determine the minimum detectable displacements or to derive, if the corresponding network is capable of detecting the expected displacements with preassumed error probabilities. In this study, minimum detectable displacements for geodetic monitoring networks are examined as well as how point-based sensitivity is impressed by datum constraints which are supplemented to the adjustment model. A horizontal control network is used to study this effect. Our experiments on this network indicate that the furthest point to the reference points, which contribute to the datum definition, yields the largest magnitude of minimum detectable displacement. That is to say the closest point to the reference points owns the lowest minimum detectable displacement. Furthermore, the displacement magnitude reduces when the number of reference points are increased in geodetic monitoring networks.

The Province of Yogyakarta is an area with high level of seismic activity in Indonesia. One of the active faults in this provice is Opak Fault, which was regarded as responsible for Yogyakarta earthquake of May 27, 2006. It is necessary to establish geodetic network for monitoring around the fault, with more detailed geologic mapping.
The research was conducted with several stages since the literature review, discussions with colleagues in the Laboratories of Geodesy and Geodynamic, Faculty of Engineering, Universitas Gadjah Mada. The first research procedure includes planning for bench-mark (BM) installation, and Global Navigation Satellite System (GNSS) data acquisition, Linux Centos V. 6.5 as Operating System and
GAMIT/GLOBK V 10.5 as scientific software for data proccesing. Measurement of monitoring network in
this area was carried out on 18 November 2013. The second research percedure was Geological observation and mapping which were conducted for about three weeks in the August 2013.
The research has established 10 BMs for monitoring network point using 3D Cartesian coordinates system. Pasive stations were labelled OPK 3, OPK 4, OPK 6, OPK 7, OPK 8, TGD 2, and active stations were labelled GK1_,KPG1,SLM1and BTL1. Distance between network monitoring stations ranges from
6,045.67385 m for the shortest distance OPK 6 to GK1_ and 4,3603.16313 m for longest distance of OPK 6 to KPG1, with precision of base lines varies from 3.94 mm to 10.61 mm, standard deviation of on the X-as (x) , Y-as (y) and Z-axis as (z) are varies. Standard deviations of 3D Cartesian coordinates system for pasive and active stations have similar pattern where y lesser than x dan z. Geological
mapping and field observation on the suspected area for the seismogenic fault suggest that the Mangunan-Muntuk region was influenced by similar tectonic forces as in 2006 earthquake.

Terrestrial laser scanners are high-accuracy 3D imaging instruments that are capable of measuring deformations with sub-millimetre level accuracy in most close-range applications. Traditionally, deformation monitoring is performed using distinct signalized targets. In this case, the centroids of these targets must be determined with great accuracy. A least-squares based target centroid extraction algorithm for planar checkerboard/chessboard targets is proposed for laser scanner data. These targets are used in a free-station network for
performing deformation analysis with no assumptions about the deformation pattern. To ensure the optimum measurement accuracy of the instrument, all systematic errors inherent to
the instrument at the time of data acquisition need to be removed. One method for reducing these systematic errors is self-calibration of terrestrial laser scanners. In this paper, this was performed on-site to model the systematic errors in the raw observations of the scanner. Post self-calibration, the accuracy of the measured translation movements were improved from the millimetre level to the sub-millimetre level.
Despite the outstanding performance of using laser scanners with signalized targets in deformation analysis, the main benefit of active sensors like terrestrial laser scanning systems is its ability to capture 3D information of the entire scene without markers. A new markerless deformation analysis technique that utilizes intersection points derived from planar-features is
proposed and tested in this paper. The extraction and intersection of planes in each point cloud can be performed automatically or semi-automatically. This new method is based on free-stationing and does not require a priori knowledge about stable control points. It can detect and measure translational and rotational movements of the planes with minimal human interaction. This paper will present both simulated and real results, demonstrating the performance of the newly proposed methodology.

The geodetic datum definition is the set of all conventions, algorithms and constants necessaries to define and realize the origin, orientation, scale and their time evolution of a Geodetic Reference System (GRS), in such a way that these attributes be accessible to the users through occupation, direct or indirect observation. (Vacaflor, J.L.,p.2647,2010).
In this work, we deal with the adjustment of a two-dimensional trilateration network constituted by “ ” physical points  , where “ ” distances  , , ,  between these points have been observed.  For the network adjustment , it is used a coordinate based formulation in a no stochastic linear model through a underdetermined consistent system of indirect linear observational equations :  ,  ,  ,  ,  number of observed distances;  number of unknown parameters  rank,  .
The network point positions are defined in a Geodetic Reference System of Cartesian Coordinate (x,y) :GRS(x,y).
The GRS(x,y) is characterized by : a) right-handed convention is adopted for the axis; b) the origin “o” is a point P not specified of the Earth ; c) the first and second rays are the ox and oy positive axis respectively with not specified orientations; d) the scale or length defined of the unit vectors along ox and oy is the meter (SI), and it is realized by the observed distances of the trilateration network.
Vector of observations (increments)

,  ,  , 
  ; 
Design or coefficient matrix (“Jacobian”)
  ; 
Vector of unknown parameters (coordinate increments).
                     
Vector of unknown coordinates  of the points  of the Geodetic Reference Frame : GRF(x,y) , expressed in the .

Vector of known coordinates  of  from the “a priori” or “approximated” .

;  ;  ,  ,

The lack of definition in the origin and orientation of the GRS(x,y) cause a datum defect and a rank-deficiency  in the design matrix  with  ,  number of datum defect.
A solution  , to the adjustment of the trilateration network called I-MINOS (Minimum Norm Solution with respect to the I –seminorm, I:= identity matrix) of  is obtained based in the optimal criterion  ,  , where  are the all other vectors solution of  . (Grafarend, E.W. and Schaffrin, B.,p.11,1993).
It is shown that the datum definition in the solution  , I-MINOS, is given through the fulfillment of  the conditions : 1) “No Net Translation” (NNT) since  , ,  ,  Identity matrix, and,  2) “No Net Rotation” (NNR) since  , . (Vacaflor, J.L.,p.2652, 2010).
As a numerical example, it is presented the datum definition in the solution , I-MINOS of the adjustment of a two-dimensional trilateration network with six points.

References

- Grafarend, W.E. and Schaffrin, B. (1993): Ausgleichungsrechnung in linearen Modellen. Mannheim;Leipzig;Wien;Zürich:BI-Wiss.-Verl. ISBN: 3-411-16381-X, 483p.

- Vacaflor, J. L. (2010): Geodetic datum and No Net Translation (NNT), No Net Rotation (NNR)  conditions from transformation parameters, a reference frame and a selection matrix. Mecánica Computacional, Vol. XXIX, Eduardo N. Dvorkin, Marcela B. Golschmit y Mario A. Storti (Eds). Asociación Argentina de Mecánica Computacional. Editorial:Imprenta Macagno S.R.L. Santa Fe. ISSN: 1666-6070, pp. 2647-2653.