Furthermore a Wide-area PSI product is being developed which could input into any of the previous themes.
The objective is to deliver European geo-information services for hydro-geological hazards affecting urban areas, mountainous areas and infrastructures.
For this purpose, a multi-hazard approach will be addressed, focusing on urban and mountainous areas, concerning the ground motion directly or indirectly connected with the hydrogeological systems. In particular, the expected causes of ground motion should be mainly linked to groundwater over-pumping and recovery from pumping, mining, above ground and underground construction and slope instability.
In the current TF stage 3, the planned activity includes approximately 13 test sites in Europe; the service baseline is structured into the following sub-themes:
Terrafirma Groundwater management products are made using and integrating several datasets acquired by ESA missions.
This allows Terrafirma to deliver geo-information and detailed analysis of wide areas in Europe where the expected causes of ground motion should be mainly linked to groundwater over-pumping, to lead to the identification of the ground displacement triggers, to measure carefully ground motion as of 1992 and to obtain a temporal evolution of the investigated event.
The ground displacements obtained by PSI measurement are combined and integrated in a Geographical Information System (GIS) with other ancillary data (topographic data, optical images, aerial photo, land use map, geological and structural data), in order to visualize the geographic relationships between the regional geological setting and the measured displacements. Moreover integration with in situ monitoring networks is foreseen.
Abandoned / Inactive mines
Abandoned mines represent a severe environmental threat, with important consequences such as sediment contamination, water and air pollution and ground instability (mine subsidence and sinkholes).
Mine subsidence can be defined as movement of the ground as result of the collapse or failure of underground mine workings; surface subsidence features usually take the form of sinkholes or wide downward shifting areas.
These phenomena are more important above shallow mines, resulting from the collapse of the roofs and pillars of underground rooms, with a consequent caving of the overlying strata and depression in the ground surface. Where the mining areas are widespread, the punctual sinkhole phenomena can develop in cluster systems, causing large subsidence, with extensive damage to structures and properties throughout the years.
This Terrafirma service is devoted to the analysis of some areas in Europe where mine subsidence is an important constraint of the urban planning, evaluating the historical trend of the phenomena; the value adding activity is related to GIS mapping, geological and structural interpretation of subsidence due to the mining activity, assessment of the relationship between limited sinkhole events and development of wide subsidence areas.
Mining Inventory (MNI)
Terrafirma Mining Inventory products (MNI) provide information on surface movements in active or abandoned mining areas using SAR data from the archive.
Mining Monitoring (MNM)
Terrafirma Mining Monitoring products (MNM) focus on the ongoing monitoring of specific mining areas using data from new programmed acquisitions.
Mountainous Area products
This service covers test sites related to slope instability in mountainous areas. During Stage 3, Terrafirma will provide InSAR data processing; the geo-interpretation will closely follow the Landslide Inventory (LSI) and Landslide Monitoring (LSM) products of the TF stage 2 detailed below:
Landslide Inventory Product (LSI)
PSI data is integrated within the inventory map in a GIS environment. The PS points are overlaid upon the pre-existing landslide inventory, when available, in order to assess the similarities and differences in spatial distribution and landslide activity with respect to the PS measurements.
Where current inventory information is in agreement with PSI data (both in terms of landslide boundaries and activity) average velocities of the PS points over landslides are computed at two different time intervals (total period and previous 2 years), and added as new fields in the landslide inventory attributes table. In the case of differences between the PSI data and landslide inventory information, multi-temporal aerial-photos and / or optical satellite imagery are analysed to provide possible explanations for variations. Only cases characterised by superficial evidence of slope movements, linked to their topography (scarps, bulges, steps, etc.) and vegetation related indicators (disrupted texture of vegetation, bent trees, grass scars, etc.) are taken into account.
Landslide Monitoring Product (LSM)
The product relies on long term PSI monitoring of superficial movements induced by specific slope movements. PSI is well suited for assessing the temporal evolution of slow landslides (up to a few centimetres per year) affecting built-up areas by providing precise measurements of ground displacements without the necessity of positioning any targets on the ground and without any physical contact with the slope. The PSI measurement points are integrated into a GIS environment with other ancillary data, such as aerial photos, topographical and geomorphological maps to obtain an accurate analysis of the spatial distribution of the ground displacements. Moreover, measurements from in-situ networks, such as inclinometers, extensometers, topographic levelling, etc., are compared with PSI displacement maps.
The objective of the Terrafirma Tectonics Theme is to provide services that present information on seismic hazards and that are oriented by the needs of the end user.
Crustal block boundaries
This service is aimed at applying standard PSI analysis to investigate surface movements and to discriminate different crustal blocks. The service will be delivered as GIS layers and databases. Three subservices can be identified as the following:
Major and local fault investigation
This service is designed to provide a monitoring along and across major faults to aid the measurement of fault slip rates and aid the estimation of locking depths. Furthermore the service is also designed to detect local active faults reactivated soon after major seismic events and eventually further surface effects triggered by major earthquakes. The service is designed to exploit the analysis of surface movement recorded at large scale by full resolution PSI products. In-situ data like GPS measurements, optical levelling, geological mapping, seismological scenarios, are combined with PSI data to perform a cross comparison, which is able to increase the effectiveness and reliability of the service. The output is GIS oriented and provides geoinformation vectors and raster layers to the end user data.
Earthquake cycle investigation
The service is addressed to provide measurement of surface deformation relative to the active faults phases. In particular, a comprehensive analysis of the earthquake cycle is a key issue for the definition of the hazard in seismic areas. The analysis of active tectonics is oriented towards the investigation of three seismic phases: pre-, co- and post-earthquake. Although the effects of the coseismic phase are now widely known and modelled accordingly by conventional Differential SAR Interferometry major issues still remain with regards to the other phases. Thus as well as the interseismic differential interferometry, the utility of this service for the end users is mostly related to the PSI techniques which allow the information gap on the interseismic phase, i.e. pre- and post- seismic phases to be filled.
The post seismic phase can be monitored to measure the amount and the surface extension of possible deformation rebound or residual strain release. This is a relevant issue for end users to estimate seismic hazard effectively. On the other hand the preseismic, or aseismic, deformation remains an open issue, in particular for its modelling complexities. Therefore the service is aimed at providing dense geodetic data to investigate possible signals of the different phases of the earthquake cycle and to understand them.
Vertical deformation sources in urban areas
This service exploits the PSI analysis applied to measuring vertical surface movements in urban areas prone to seismic risk. The PSI analysis aims to strengthen the scientific database to investigate the cause of subsidence and to identify the source (tectonic vs. non-tectonic/manmade) of such effects. The measurement and monitoring of vertical deformation sources in urban areas is a major issue.
The PSI data is compared with in situ measurements from levelling and GPS in order to cross-validate the results. The end user then receives a GIS project, containing, in vector or raster format, each specific set of data: the PSI layer, the geological background, the seismicity and the above-mentioned geodetic measures. .
Soil vulnerability maps
The PSI technique is a unique tool for providing very dense spatial data and detailed measurements of surface displacements, which are useful input to be added to in-situ measurements in order to compute vulnerability maps. The PSI maps are at full resolution since the target is the single building and/or single infrastructure. Value added products result from the integration between PSI maps and local data. The service contributes to the investigation of possible causes of surface movements as well, providing the discrimination between primary tectonic displacements and seismically induced movements. Moreover this approach allows the investigation of the effects of soil compression due to overimposing a litostatic load. According to its geotechnical properties, soil can be affected by primary consolidation subsidence rates for some years, afterwards asymptotically trending to a stable condition. Whereas when a fast, spatially localised, differential soil movement is measured the structures above are certainly more prone to structural damage than in areas of homogeneous subsidence. Consequently vulnerability more probably increases in the former than in the latter scenario. All products are available in a GIS environment.
Furthermore, PSI techniques can be used to perform the monitoring of built areas and strategic infrastructures in the selected seismic areas. Indeed, besides the investigation of soil vulnerability, this service focuses on the structures above, such as buildings, bridges, power plants and dams within or nearby the risk areas.
An important topic is the study of the geological properties of subsoil in and around urban areas prone to earthquakes. It is worth noting that besides primary effects (faulting and ground shaking) of earthquakes, secondary effects such as liquefaction, ground/slope failure and subsidence are major issues too. Unconsolidated soft soils commonly amplify ground shaking up to reach resonance conditions if specific ground properties and quake duration occur. Specific analyses are then useful to properly evaluate the vulnerability and the hazard, in particular microzonations site effects (soft ground effects and liquefaction analysis), which occur in the presence of soft soils due to their thickness, properties and earthquake type (magnitude, depth). The surface deformation and soil shaking have an impact on structures as seismic waves affect man-made structures proportionally to peak acceleration.
The microzonation is obtained by performing borehole analysis, geophysical profiles, seismic profiles and using geological maps. These latter contain the soil class differentiations, and according to the EuroCode8 previsions, EC8, all geological units have been unified in five different classes with associated geophysical parameters relevant to their behaviour with respect to an earthquake.
In order to compute vulnerability analysis a building inventory is required including the definition of several parameters. The vulnerability of buildings is coded and classified in the vulnerability inventory database, and it is defined as the degree of loss to a given element at risk resulting from the occurrence of a hazard. Vulnerability assessments are usually based on past earthquake damages and it is a measure of the damage that a building is likely to experience given that it is subjected to a ground shaking of specified intensity. The structural vulnerabilities have been classified in six different classes, from A to F, by the 1998 European Macroseismic Scale (EMS, 1998). For example, in the Istanbul test case most of the buildings belong to the class C: Reinforced Concrete buildings with low levels of earthquake resistant design. The EMS98 damage scale defines five damage classes from the less damaged buildings (Grade 1) up to the complete destruction (Grade 5) for each typology of construction.
Coastal Lowland Subsidence & Flood Defense theme
This theme reflects Terrafirma’s approach as it is envisaged to demonstrate and promote the value of PSI in coping with one of the potentially most damaging natural hazards that affect large areas in Europe. The Coastal Lowland Subsidence & Flood Defense Theme directly relates to the EU-Flood Directive (Directive 2007/60/EC) on the assessment and management of flood risks, which entered into force on 26 November 2007. This Directive now requires Member States to assess whether any water courses and coastlines are at risk of flooding, to map the flood extent and assets and humans at risk in these areas and to take adequate and coordinated measures to reduce this flood risk. This Directive also reinforces the rights of the public to access this information and to have a say in the planning process. The Directive requires Member States to first carry out a preliminary assessment by 2011 to identify the river basins and associated coastal areas at risk of flooding. For such zones they would then need to draw up Coastal Lowland Subsidence & Flood Defense risk maps by 2013 and establish Coastal Lowland Subsidence & Flood Defense risk management plans focused on prevention, protection and preparedness by 2015. The Directive applies to inland waters as well as to all coastal waters across the whole territory of the EU.
From these requisites four types of services are envisioned for the TF Stage 3-Coastal Lowland Subsidence & Flood Defense theme:
Basic PSI-Wide Area Service
This service takes the form of a basic PSI-service in that it will deliver a PSI-derived GIS-layer and database. Specifically for Coastal Lowland Subsidence & Flood Defense Hazard mapping, wide areas will be processed by combining multiple scenes, in order to be of use to water management agencies responsible for large basin or floodplain areas. Digital Terrain Models (DTMs) can be derived as a by-product from the PSI-processing and are of high value for flood risk analysis. This service is not to be considered as a standalone service but can be delivered if requested. The wide-area mapping service (which must address a series of requirements including scalability to European coverage and use of other data) has as one of its objectives the possibility to be used as the input to the Subsidence Hazard mapping service for flood prone areas.
Subsidence Hazard mapping service for flood prone areas
This service envisions the integration of the basic PSI-Wide Area Service with ground truth data, notably levelling data and GPS, and geological data and information in order to develop a service which enables users to interpret subsidence maps within their geodetic reference system of use and to assess mechanisms of subsidence risk. Mostly, these maps show contours of equal subsidence rate or delineated subsiding areas.
Flood defence monitoring service
This is a focused application of PSI monitoring and evaluation of coastal defences and flood protection systems. This application demonstrates the applicability of PSI for pinpointing and monitoring localized phenomena along flood protection systems. Applications can be foreseen within the context of coastal defence structures as well as along fluvial defence systems around Europe.
Advanced subsidence modelling service for flood prone areas
This application builds upon the mapping and monitoring services for flood prone areas. PSI, as one of the available sources of geodetic information, can be used in combination with geomechanical modelling to assess and quantify the mechanisms contributing to subsidence or failure of flood defence structures. The modelling service is an advanced service which can only be delivered on a case-by-case basis. Potential end-users include engineering consultants, water management authorities and Public Works authorities. Typically, any such product will give quantitative estimations of geomechanical properties which determine the rate of subsidence or settlement, like compressibility of the geological strata or engineered ground works.