Analytical methodologies
In order to establish and develop studies within the tree thematic areas a combination of multidisciplinary techniques and measurements will be employed. These disciplines, that include geophysics, geology, geochronology, etc., characterize the different physical properties of the materials. Topo-Iberia aims to increase in an unprecedented maner the amount of experimental information with the implementation/instalation of a relatively large intrument pool that will perform measurements of physical observables usable by the different disciplines.
The methodologies which will be used in this research project include:
- Passive seismic methods (Earthquake recordings)
- Geodetic GPS measurements of deformation
- Magnetotellurics
- Gravity, magnetics and paleomagnetism
- Quantitative analysis of the topography
- Dating methods
- Analog and numerical modelling
- Detection and characterization of seismogenic structures
- Determination of the velocity of formation of topographic relief
Passive seismic methods (Earthquake recordings)
Most seismic methods to be used will be based on earthquake recording data at local, regional and teleseismic scales. For this purpose, a dense temporal network of broad band digital recording intruments will be deployed successively within the three areas of interest: north, centre and south of the iberian peninsula.
It is intended that this network will be composed of 80 seismic recorders. The network will be deployed in a 50 or 60 km grid, taking into account the existing stations from the spanish permanent networks. Considering that the number of seismographs it is not enough to deploy a network over the entire iberian peninsula with the required density, it is planned to make three sequential deployments spreading over the southern, central and northern peninsular areas.
Map showing current and historic state of the IberArray seismographic network (spring 2012). Red marks indicate previous places of portable seismographs, green marks pinpoint active stations, and yellow marks show locations of stations that belong to networks managed by other institutions.
The information about installation, maintenance and current state of stations that make up the seismographic network can be looked up in the IberArray website: http://iberarray.ictja.csic.es/, whereas the records of seismographs can be downloaded through the SiTopo web site: http://cuarzo.igme.es/sitopo/.
The seismic records acquired with this instrument set up can be analyed using different methodologies aiming at different objectives:
- Earthquake location with advanced techniques
- Seismic tomography
- Receiver functions
- Seismic anisotropy
Geodetic GPS measurements of deformation
GPS can be used as a tool for the measurement of the active deformation providing a way of monitoring active tectonics and the detection of relatively slow movements, as is the case of the iberia peninsula. A fundamental objective of this project involves the determination of the present day deformation vectors of the crust. The aditional data acquired aims to constrain the present causes of this deformation.
It is proposed to deploy a network of 25 GPS for 30 months recording continuously. Such deployment will cover several transects along iberian peninsula boundaries, including north of Africa, and strategic areas complemented by the existing instrumentation.
Deployment of IberArray GPS stations
IberArray GPS network leaflet - IberArray GPS network report - GPS preliminary results poster
Magnetotellurics
The magnetotelluric methodology is based on measurements of the variation of the Earth's electrical and magnetic fields. These measurements provide the main constraints in order to estimate conductivity models of the Earth's lithosphere. Here is proposed to realize new profiles to achieve integrated transects at the whole scale. In parallel, two permanent stations of very long period (105 s) will be installed.
In the southern domain, two orthogonal profiles are proposed in the Western part of the Betics, where few data on crustal structure are available. Both profiles traverse sismogenetic zones, such as the Granada depression or the Malaga surroundings.
In the Rif cordillera there will be two other profiles perpendicular to the main structures.
In the central domain, a NW-SE profile will characterize the alpine structure of the Central System, and another profile will run coincidently with a seismic refraction profile recently acquired. A third MT profile in the easternmost part of the Central-Iberian zone will be recorded coincident with the deep seismic reflection profile "Alcudia".
Magnetotelluric profiles proposed (black) and already existing (red) in the different sectors of study. Magnetotelluric profiles done within the frame of Topo-Iberia project (yellow).
Gravity, magnetics and paleomagnetism
This project should also contribute to the determination of a dense grid of measurments on potential fields such as gravity and magnetism. The data acquisition effort is directed toward filling in the gaps and acquiring complete transects that could extend from the iberian peninsula in to Northern Africa to constrain the lithospheric models in this controvertial area.
Additional dense grid acquisition is planned in sedimentary basins, and dense magnetic grids in regions where intense anomalies have been located (Pirite Belt). These anomallies can be correlated to mafic-untramafic bodies of mantle origin.
Detailed potential field measurements are required to determine the structure of the upper crust, and the depth to basement and the overall distribution of sedimentary basins. This is very important in order to calculate the isostatic effects in 3-D and be able to separate the contributions of the crust and mantle to the topography, and also to identify zones which are not in equilibrium, thus where the topography is not supported dynamically.
Quantitative analysis of the topography
Digital topographic models (DTM) include the topography of surface land and the bathimetry marine basins, continental margins, etc. This data is integrated through a geographical information system (GIS).
These are main tools to perform a detailed analysis of the surface topography, obtaining geomorphological indexes in mountain fronts, drainage basins and continental margins. This is a convenient tool to build slope maps, mandatory for assesment of land slides.
Dating methods
Establishing the rates of uplift and the rates of surface evolution requires the use of dating methods. Methods allowing to obtain information at complementary timescales will be used.
- Termochronology based on Fission Tracks and U-Th/(He)
- In Situ cosmogenic isotopes
Analog and numerical modelling
Numerical modeling includes mainly two aspects:
- Static characterization of structures
- Internal architecture and dynamic evolution model of the previously defined structures, which includes cinematic and dynamic models.
Analog modeling refers to simulating the lithosphere evolution in specific scenarios and with structures and materials with specific physical properties.
Is intended to develop the following models:
- Integrated models for the characterization of the crust and upper mantle
- Lithospheric deformation, numeric simulation
- Numerical deformation of the dynamics of superficial processess
- Analogic simulation
Detection and characterization of seismogenic structures
Two groups of seismogenic faults can be distinguished: those active within the historical period and those that remained silent (but are still seismogenic). Different approaches are proposed for each group.
- Seismogenic faults that generate instrumental earthquakes: The inversion of the regional seismic tensor provides information on the active geologic structures.
- Seismogenic faults that have remained silent within the historical period: Paleoseismology
Determination of the velocity of formation of topographic relief
Denudation and uplift velocities in surface exposed areas can be achieved by dating the deposits and geomorphological surfaces. The distribution of the shallow deposits since Middle Miocene provides constraints in uplift estimates since the time of their formation. Precise indicators of the position of the old coast line during the recent Quaternary, and the beach deposits and “trottoirs” provide knowledge on active structures.
The “calcretas” within the alluvial fans and the fluvial terraces and “travertinos” on top of the drainage network, are features of special interest for this velocity determination. Methods commonly used for dating include cosmogenics in situ (10Be), U/Th, and 14C.
