SATELLITE MONITORING
FOR A SAFER CONSTRUCTION ENVIRONMENT
S. F. BALAN1, V. PONCOS2, D. TELEAGA2, R. NICOLAE3, B.F. APOSTOL1
1 National Institute of Research and Development for Earth Physics, Magurele-Bucharest, Romania 2 Terrasigna, Bucharest, Romania
3 RATEN – Centre of Technology and Engineering for Nuclear Projects, Magurele-Bucharest, Romania
Received October 12, 2015
The results of Permanent Scaterrers Interferometry (PSI) technique is employed
herein in order to identify some seismic risk features in certain zones of interest, such
as Bucharest city area, capital of Romania, and the Nuclear Power Plant in
Cernavoda. A comparison is also made between in-situ and satellite monitoring. A
dense sampling of the structures in terms of temporal deformation profiles is provided
and further used to assess the stability and resilience of buildings. All these
information are corroborated with seismic hazard maps in terms of peak ground
accelerations (Bucharest case), highlighting areas with high-risk probability.
Advanced satellite interferometric techniques help locate certain regional or local
anomalies exemplified by ground uplifting or subsidence. These movements can be
general when large areas are involved, (Bucharest city case), or they may occur on
small areas, (Cernavoda city buildings) or those related to the zone of lake “Lacul
Morii”, consisting of artificial filling areas.
Key words: synthetic aperture radar, satellite, earthquake, settlement, microzoning.
1. INTRODUCTION
This paper presents applications of the InSAR (Interferometric Synthetic
Aperture Radar) technique to mitigate the seismic risk of two important zones in
Romania. The first zone is Bucharest Metropolis, the capital of Romania, and the
second zone is Cernavoda, the site of a nuclear power plant.
The results presented in this paper originate in the work conducted by
Terrasigna Ltd, National Institute of Research and Development for Earth Physics
(NIEP) and Centre of Technology and Engineering for Nuclear Projects (RATEN
CITON) – some of the participants in the project “Spaceborne Multiple Aperture
Interferometry and Sequential Patterns Extraction Techniques for Accurate
Directional Ground and Infrastructure Stability Measurements”. Terrasigna applied
the Persistent Scatterrer Interferometry (PSI) technique to extract the ground
deformation in Bucharest during July 2011 – January 2013, and at Cernavoda from
June 2013 to June 2014, from series of TerraSAR-X satellite images. NIEP is in
Rom. Journ. Phys., Vol. 61, Nos. 5–6, P. 1108–1119, Bucharest, 2016
2 Satellite monitoring for a safer construction environment 1009
charge of the seismic network and data processing for the whole Romania, using a
consistent number of seismic digital stations both in Bucharest and at Cernavoda
site; RATEN-CITON is responsible of the observations on Cernavoda grounds and
their data processing.
Both locations, Bucharest Metropolis and Cernavoda, are prone to strong
earthquakes from Vrancea region as those in the last century: November 10, 1940,
magnitude 7.4 on the Richter Scale; March 4, 1977, Mw = 7.4; August 30, 1986;
Mw = 7.1 and May 30, 1990, Mw = 6.9. In the seismic event of 1940 some several
hundred victims were reported; in 1977, about 1500 people died and major
building damage of both earthquakes were recorded, most of them in Bucharest.
2. GEOLOGICAL DATA ABOUT BUCHAREST AND CERNAVODA
Bucharest, the capital of Romania (Fig. 1), with more than 2.5 million
inhabitants, is considered, after Istanbul, the second-most earthquake-endangered
metropolis in Europe. It is identified as a natural disaster hotspot by a global study
of the World Bank and Columbia University [1]. All disastrous earthquakes, as
those presented above in the 20-th century, are generated within a small epicentral
area – the Vrancea region – about 150 km northeast of Bucharest, and about
250 km northwest of Cernavoda (Fig. 1).
Thick unconsolidated sedimentary layers in the area of Bucharest amplify the
seismic shear-waves which may cause severe destruction. [2, 3, 4] Thus, disaster
prevention and mitigation of earthquake effects is an issue of highest priority for
Bucharest and its population. Bucharest is located in the central part of Plain Vlasia
(Fig. 1), which is part of the Romanian Plain, and is approximately 165km from
Vrancea epicentral zone (Fig. 1). Plain Vlasia is considered by some authors [5, 6]
a transition zone between the northern piedmont plains and the Danube plain in the
South. It runs between Prahova valley north and Arges valley in the south and is a
continuation of the common alluvial cones of the rivers Ialomita and Dambovita.
Along these watercourses the altitude decreases slightly, with small fluctuations
from northwest to southeast and a relatively constant average slope value (0.5–
0.6 m/km). Cross-slopes have high values, especially on the right riverbank.
In the city, Dambovita valley looks like a long corridor approximately 22 km
long. Its width varies from 650 m opposite the Botanical Garden, to about 4 km at
the eastern end of the village Catelu (before being regularized in the last century).
There are lakes in the city, for example at the Park Carol and Youth Park, on
the right bank of Damboviţa, and Lake Cismigiu on the left bank. The lake “Lacul
Morii” (the Lake of the Mill) is an unusual feature, formed by the dam on river
Dambovita in the Ciurel zone, in the 20th century.
Geological, geotechnical and hydrogeological drillings in the city have made
it possible to know what is included in successive subsoil deposits.
1010 S.F. Balan et al. 3
Fig. 1 – Location map of Bucharest and Cernavoda in Romania.
Cernavoda area is located in the great geological, morphological, tectonic
and structural unit South Dobrogea. This structural unit is bounded on the North by
Ovidiu-Capidava fault, South by Shabla-Calarasi-Urziceni partially identified fault,
at West by the Danube fault and East by the Black Sea. The folded fundament of
this region consists of weak metamorphic sedimentary series of Proterozoic age,
known as green schists. These types of sediments have been encountered in a
borehole on the right side of Danube River, near Cernavoda city, at 1192 m depth.
From lithological point of view, the zone consists of an alternation of sandstones and
chlorites schist.
The sedimentary layer, discordant over the Palaeozoic fundament, consists
of deposits belonging to periods Jurassic, Cretaceous, tertiary and quaternary.
4 Satellite monitoring for a safer construction environment 1011
Quaternary is represented by inferior Pleistocene deposits which consist of
reddish clays with limestone concretions of no more than 5 m thickness, covered by
loess up to 45 m thickness, belonging to medium and inferior Pleistocene.
From the structural point of view, Dobrogea belongs to Wallachia-South
Dobrogea sector. In this unit there are two tectonic elements, namely a heavy folded
fundament and a sedimentary layer with slightly or even unfolded deposits.
From a morphological perspective, the site lies within the floodplain of Carasu
Valley, characterized by a flat relief, with low slopes, which does not encourage rapid
deployment of geomorphological processes.
3. SATELLITE MAPS AND PROCESSING
The development of spaceborne Synthetic Aperture Radar (SAR)
interferometric techniques started in 1992 after the launch of the ERS-1 mission of
the European Space Agency and since then it is continuously advancing and
gaining importance in geosciences. DInSAR (Differential InSAR) techniques have
been successfully applied for measuring the effects of a large spectrum of
phenomena, such as: deformation induced by volcanic activity, co-seismic and
post-seismic motions, glaciology, mining and groundwater related subsidence as
well as measurement of soil moisture.
However, since the SAR measurements may be affected by residual
topography and atmospheric perturbations, new techniques using large datasets
were developed. Permanent Scatterers Interferometry (PSI) [7] was the leap the
SAR technology needed to enter the domain of Geodesy where temporal
deformation profiles with millimetres accuracy are possible. TERRASIGNA
delivered InSAR-based results in terms of deformation maps showing the rate of
the displacement field with applications to landslide monitoring [8], mine tailing
ponds monitoring [9], urban site monitoring, or Danube Delta monitoring [10].
Based on the ground deformation satellite map, we can identify some seismic
risk (hazard and vulnerability) in zones of interest, in our case Bucharest
Metropolis and Cernavoda. The map reveals local ups and downs on the surface,
which could have different causes.
If there is a large settlement and structural cracks would appear, even almost
unnoticed, and an earthquake of magnitude more than 7 would come, (3 of such
events were in Romania in the XX-th century: in the year 1940 with magnitude
MW = 7.6; year 1977, with magnitude MW = 7.4, year 1986, with magnitude MW =
= 7.1) then the buildings could suffer damages.
1012 S.F. Balan et al. 5
This is why it is very useful to know that a large settlement have occurred,
because it could affect structure of the buildings and, in the case of a strong
earthquake, may increase the risk of damage.
Fig. 2 – Persistent Scatterrer Interferometry displacement map of Bucharest
(July 2011–January 2013).
From Persistent Scatterrer Interferometry (PSI) displacement map of
Bucharest surface (Fig. 2) we could notice that the N – W part tends to lift and the
S – E part tends to lower. These trends cannot be attributed to earthquakes, being
of moderate magnitude and in small numbers in the time range considered: July
2011–January 2013.
The trends seen in Fig. 2 are due to basement lithology and geological
composition of Bucharest.
6 Satellite monitoring for a safer construction environment 1013
Fig. 3 – Map of mean deformation rate for 395 radar points located on Nuclear Power Plant
Cernavoda (NPP-Cernavoda) Office Building.
Fig. 4 – Displacement profiles for 7 radar points corresponding to leveling mark P2.
In the case of Cernavoda site, satellite monitoring is more complete, being
accompanied also by in-situ monitoring.
For exemplification we present such a study for an office building,
belonging to Cernavoda compound.
In Figure 3 radar measurements are presented (395 points), in Figure 4
displacement profiles are shown for 7 radar points corresponding to leveling mark
P2, and in Figure 5 in-situ measurements are included (8 leveling marks) for an
office building in the Nuclear Power Plant (NPP) Cernavoda compound during the
period June 2013–June 2014. Level mark P2 could be observed in both satellite and
in-situ measurements.
1014 S.F. Balan et al. 7
Fig. 5 – Vertical displacements measured on 8 levelling marks from the Nuclear Power Plant
Cernavoda Office Building (left) during May 2013–May 2014.
Another example is the comparison between the measurements obtained with
satellite-radar and in-situ in a point on Interim Radioactive Waste Storage Building
(DIDR) of the NPP Cernavoda. In Figure 6 we can see the building on the upper
right part and in Figure 7 we could observe the temporal displacement profiles for a
point (D10) on the building obtained from in-situ and radar measurements during
2002–2009.
Fig. 6 – Interim Radioactive Waste Storage Building (DIDR) of the NPP Cernavoda
(upper-right part of the figure).
8 Satellite monitoring for a safer construction environment 1015
Fig. 7 – Temporal displacement profiles for the point D10 on the building obtained from in-situ and
radar measurements during 2002–2009.
In the map of Figure 2 we may notice red colored areas near river Colentina. The red colored areas according to figure caption are areas which are subsiding in the time of measurement more than those in their immediate vicinity. According to our interpretation (Fig. 8), in these areas the settlement phenomenon on relatively soft soil is noticed, mainly areas with artificial fillings, near actual or former riverbeds. The artificial filling areas are also noted in the seismic microzonation map of Mandrescu et al., 2007 [11], (marked by a black contour line) but now their instability is clearly proved by the Persistent Scatterrer Interferometry result (Fig. 8).
Fig. 8 – PSI deformation during 2011–2014 of the central part of Bucharest; this zone is overlaid
with a layer of old artificial fillings areas (in Bucharest, near river Colentina).
1016 S.F. Balan et al. 9
On Cernavoda site we could observe also by satellite a slow-subsidence (red)
and risk of land-slides (blue) (Fig. 9).
A particularly interesting situation seen in Figure 10 is an area near lake
“Lacul Morii”, city of Bucharest, where a portion of land is sinking in an area that
rises. The diagram made by Terrasigna Ltd. shows that this portion sunk with 10
mm in the period July 2011–January 2013 compared to surrounding areas. In this
situation satellite measurements are of particular importance, highlighting a local
area with risk due to descending movements in which it is involved.
Further, we have used a seismic hazard map of Bucharest Metropolitan Area
for peak ground accelerations (PGA) (cm/s2) from Marmureanu et al., 2010 [12].
The earthquake used to generate this map was a synthetically one, with magnitude
MGR = 7.5, from Vrancea source, with strong and well-defined acceleration in the
area. We chose this option, the strongest design earthquake, because this is the only
way we can get an image of the high acceleration areas of the Bucharest
metropolitan area.
Fig. 9 – Deformation map of Nuclear Power Plant Cernavoda area (June 2013–June 2014).
This acceleration map from Marmureanu et al., 2010 [12] is superimposed
on Fig. 2 resulting in Fig. 11.
What could be seen on this overlap of maps are large accelerations, between
250–280 cm/s2 and uplifting areas (up to ~2mm/year), situated in the north-western
part of the city, and between 270–290 cm/s2, in areas going down between 2 to 3.9
mm/year, in the south-eastern part, in the former floodplains of Dambovita. The
10 Satellite monitoring for a safer construction environment 1017
amplifications of the seismic signal, generated by these soft soils, may increase the
risk of damage to buildings in the area, in the case of strong earthquakes.
Fig. 10 – Detail from deformation map in Fig. 2, with temporal displacement profile representative
for a local subsidence in the northern region of the Lake Lacul Morii.
Fig. 11 – Acceleration map from Marmureanu et al., 2010 [12] superimposed
on radar deformation map from Fig. 2.
1018 S.F. Balan et al. 11
4. CONCLUSIONS
The points discussed in the paper show the great importance of satellite
observations, which identify areas with hazard potential generating seismic risk.
The seismic risk considered here includes local seismic hazard places, with high
acceleration and vulnerability of buildings in Bucharest [13] and Cernavoda area.
For zones showing subsidence, especially if their spatial extent is well
delimited, a settlement might have occurred, because of natural soft land or man-
made causes (artificial fillings). It is very important to locate these spots and to
know about these trends because the soil strata move there. It is also important to
know what kind of buildings are located in the area, what kind of structure they
have, if they were affected before by repairs or previous earthquakes. These soil
movements can produce extra stress in the building structure and during an
earthquake, this extra stress can develop some extra damage (cracks in different
structure elements, displacements of interior walls, damage in floors and interior
installations, etc.). If this damage is non-structural it will be repaired quickly, but if
the deterioration is in structural elements, it can endanger the stability of the
building.
The vulnerability of buildings could emerge if they are subjected to stress-
strain induced by local settlements on which overlap stress-strains from strong
earthquakes. High resolution InSAR data, as those used in the Cernavoda
monitoring, are useful to identify non-uniform settlements of individual buildings.
We have made in this paper a comparison between in-situ and satellite
monitoring. Conventional methods of monitoring are limited to visual inspection
and topo-geodesic measurements through geometric leveling method, in only a few
points from the structure.
By applying Persistent Scatterrer Interferometry technique a very dense
sampling of the structure could be provided. These observations can be used to
assess the stability and resilience of structures, leading to a better risk assessment.
Advanced InSAR interferometric techniques help locate certain regional or
local anomalies exemplified by ground uplifting or subsidence. The satellite
observations certified some previous known artificial fillings areas, identified by
Mandrescu et al., 2007 [11]. These movements can be general when large areas are
involved, (Bucharest case), or they may occur on small areas, (Cernavoda
buildings) or those related to the zone of Lake Lacul Morii, consisting of artificial
filling areas.
Acknowledgements. This work was supported by the Romanian Executive Agency for Higher
Education, Research, Development and Innovation Funding (UEFISCDI) through the project
Spaceborne Multiple Aperture and Sequential Patterns Extraction Techniques for Accurate
Directional Ground Control and Infrastructure Stability Measurements (DGI-SAR), contract no.
200/2012, Partnerships Program, PN-II-PT-PCCA-2011-3.2-1448.
12 Satellite monitoring for a safer construction environment 1019
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