Modelo de geoprocesamiento QGIS para simplificar el análisis de microzonificación sísmica de primer nivel

The Institute of Environmental Geology and Geoengineering (IGAG) of the National Research Council (CNR) is located in Rome, in the Area of Research «Roma 1». It was founded in 2002 by regrouping five former research Institutes and Centers that had been active for more than 40 years in their field of expertise. IGAG covers a wide range of scientific topics in the field of Earth sciences, mainly focusing towards the study of:

  • Geoquímica ambiental y remediación de suelos y aguas contaminados;
  • Depósitos minerales y procesamiento mineral, incluyendo el tratamiento de desechos;
  • Geoingeniería y seguridad de las excavaciones de roca;
  • Evolución geológica reciente;
  • Mitigación de desastres naturales;
  • Geoarqueología y arqueometría.
  • Geología Marina
  • Geomática, análisis y desarrollo SIG.

The level 1 seismic microzonation study of the Pietramontecorvino area (Apulia, Southern Italy, located along the Central-Southern Apennine chain) is part of a project, in collaboration with the Basin Authority of Apulia (Puglia AdB) and the Department of Geology and Geophysics (DGG) of the University of Bari, aimed at the seismic microzonation of 63 Municipalities of the area of Foggia. The activity was promoted by the Italian Department of Civil Protection (DPC) and financed by the Interministerial Committee for Economic Planning (CIPE n. 20/2004).

Herramienta de geoprocesamiento QGIS para estudios sísmicos de microzonificación de primer nivel

The seismic microzonation evaluate the seismic hazard at the local scale proposing to identify areas of territory characterized by homogeneous seismic behavior. The first level of seismic microzoning has the purpose of defining the lithological properties and geometry of geological units that characterize these portions of territory (microzones).

The observation of the damage caused by an earthquake often shows variations at local scale caused not only by geological structures but also by different quality and type of building structures, resulting in different seismic hazards.

The seismic microzonation evaluates the local seismic hazard, through the identification of areas of territory characterized by homogeneous seismic behavior.

The Guidelines and Criteria for Seismic microzoning 2008 (http://www.protezionecivile.gov.it/jcms/it/view_pub.wp?contentId=PUB1137) provide standards for seismic microzoning studies on Italian territory; they distinguish three levels of increasing depth (from 1 to 3).

The first level seismic microzonation consists in the creation of three thematic maps:

  1. Mapa de inspección conteniendo las inspecciones para estudios de microzonificación sísmica;
  2. Geo-lithological map, obtained from detailed scale geological and geomorphological maps integrating existing lithological, stratigraphic and geotechnical data related to surveys;
  3. Level 1 seismic microzonation map (the principal product of level 1 microzonation), identifying the microzones into three categories of local hazards:
    • Zonas estables;
    • Zonas estables susceptibles a amplificación del suelo;
    • Zonas inestables.

The scope of this work is to contribute to the creation of a methodology for processing topographical, geological, geophysical and geo-technical data aimed at level 1 seismic microzonation map drafting, through the use of open source tools.

The Graphical Modeler tool integrated in the latest version of QGIS (2.8.1 as of writing) has been used for the creation of a simple geoprocessing model. This tool is useful to automate one of the analysis commonly performed for the creation of level 1 seismic microzonation maps, in particular to identify unstable zones as polygon features.

El modelo hace uso de diferentes software y bibliotecas de código abierto (GRASS, GDAL, QGIS), demonstrando la utilidad de QGIS como un interfaz simplificado y unificado para herramientas SGLCA (Software Geoespacial Libre y Código Abierto) (Fig. 1).

Geoprocessing model

(Fig. 1) Captura de pantalla del modelo de geoprocesamiento.

El modelo toma como entrada (Fig. 2):

  • Un shapefile de líneas contorno que contiene un campo con valores de elevación;
  • El nombre del campo que contiene valores de elevación;
  • La resolución deseable del ráster en metros para el MDT y Pendiente (predeterminada 10);
  • Se extraerá un shapefile polígono con elementos que intersectan áreas con pendiente mayor a 15 grados;
  • El nombre de la capa polígono resultante.
Model input form (left) and execution log (right)

(Fig. 2) Formulario de entrada del modelo (izquierd) y registro de ejecución (derecha).

Cuando se lanza, el modelo realiza las siguientes operaciones:

  • The GRASS tool v.to.rast.attribute converts contour elevation lines to raster, taking the contour shapefile, the name of the z field and the raster resolution as input;
  • The GRASS tool r.surf.contour generates the elevation model taking as input the rasterized temporary output from previous step and the raster resolution;
  • La herramienta GDAL «gdaldem» genera la pendiente expresada como grados a partir del modelo de elevación;
  • La herramienta GRASS r.mapcalculator es usada para generar un ráster de 1 bit que identifica áreas con pendiente mayor que 15 grados (este valor está codificado en las guías de microzonificación, de manera que es fijo), usando la expresión:

if(A>15,1,null())

donde A es el ráster temporal generado por gdaldem;

  • La herramienta GDAL «gdal_polygonize» convierte el ráster de 1 bit a polígonos;
  • La herramienta QGIS «Intersección» es usada para sobreponer las áreas con pendiente mayor a 15 grados con la capa escogida de intersección.

The result is a polygon layer with areas prone to instability due to a slope value greater than 15 degrees, automatically extracted from a thematic map such as a landslides polygon layer (Fig. 3) or a lithological map.

The model output (in red) shows highly unstable areas extracted from a landslides layer (orange)

(Fig. 3) The model output (in red) shows highly unstable areas extracted from a landslides layer (orange).

Conclusiones

This work clearly demonstrates that open source GIS tools like QGIS, GRASS, GDAL/OGR, can successfully be used for spatial analysis and data processing aimed at first level seismic microzonation studies. In this example work, QGIS has been used as a simplified and unified interface for different high quality GFOSS tools; the Graphical Modeler allows to intuitively construct geoprocessing models that can be easily shared as portable and cross-platform tools that doesn’t require expensive software licenses. The tool leverages the QGIS modeling capabilities to graphically chain different algorithms, defining input and output parameters and leaving to the software the task of managing intermediate data output. The use of GRASS algorithms does not require defining and using a GRASS database and mapset, greatly simplifying the design of the model. Future developments include the creation of a package of tools and models, based on open source software, that can be used to simplify and speed up spatial analysis tasks necessary for seismic microzonation studies.

Referencias

  • G. Baldassarre; Gallicchio, S.; Giannandrea, P. & Tropeano, M.: «Relazione Finale Geolitologica per la microzonazione sismica di livello 1dei Comuni della Provincia di Foggia Dipartimento di Geologia e Geofisica dell’Università di Bari, 2011»
  • Cavinato,G.P.; Cavuoto, G.; Coltella, M.; Cosentino, G.; Paolucci, E.; Peronace, E. & Simionato, M.: «Studio di fattibilità per il monitoraggio e la messa in sicurezza delle aree urbane a rischio di stabilità statica e vulnerabilità strutturale del Comune e della Provincia di Foggia - CIPE 20/2004 Consiglio Nazionale delle Ricerche - Istituto di Geologia Ambientale e Geoingegneria, 2013, 526»
  • Contributi per l’aggiornamento degli «Indirizzi e criteri per la microzonazione sismica » 2008. Ingegneria sismica, Pàtron Editore Bologna, 2011 (http://www.protezionecivile.gov.it/jcms/it/view_pub.wp?contentId=PUB28083)
  • Gruppo di lavoro MS, 2008. Indirizzi e criteri per la microzonazione sismica. Conferenza delle Regioni e delle Province autonome - Dipartimento della protezione civile, Roma, 3 vol. e Dvd, Presidenza del Consiglio dei Ministri, Dipartimento di Protezione Civile, 2008, 424. (http://www.protezionecivile.gov.it/jcms/it/view_pub.wp?contentId=PUB1137)

Autores

Este artículo fue contribuído en Marzo 2015 por Giuseppe Cosentino y Francesco Pennica (www.igag.cnr.it).

Giuseppe Cosentino

Giuseppe Cosentino

Giuseppe Cosentino <g.cosentino@igag.cnr.it> is geologist and technologist specializied in Geographic Information Systems for the management of geological and engineering hazards. Currently working in the field of seismic microzonation and environmental characterization of the lands in contaminated sites. Areas of interest: geological and environmental hazards, cartography, structural geology, explorative drillings.

Francesco Pennica

Francesco Pennica

Francesco Pennica provides GIS and WebGIS software development and data management: GeoServer, MapServer, ArcGIS Server, GeoNetwork OGC standard based webgis services, Java, HTML, CSS, Javascript, Python, PHP languages and frameworks, WebGIS front-end development with OpenLayers, ExtJS, GeoExt, JQuery, GWT, Ext-GWT, Google Maps API SQL, geodatabase management, PostgreSQL, PostGIS, GIS desktop software based analysis and scripting (ArcGIS, GRASS, GFOSS tools), Software configuration and management in Linux and Windows based servers and desktops.