MAHA: A comprehensive system for the storage and visualization of subsoil data for seismic microzonation

Abstract

MAHA is a database-centred software system for the storage and visualization of subsoil data used for the production of seismic microzonation maps in Italy. The application was implemented using open source software in order to grant its maximum diffusion and customization. A conceptual model of the subsoil, jointly developed by the Italian National Research Council and the National Department of Civil Protection, inspired the structure of the underlying database, consisting of 15 tables, 3 of which of spatial nature to accommodate geo-referenced data associated to points, lines and polygons. A web-GIS interface acts as a bridge between the user and the database, drives the input of geo-referenced data and enables the users to formulate different types of spatial queries. A series of forms designed “ad hoc” and enriched with combo boxes provide guided procedures to maximize the fluency of data entry and to reduce the possibility of erroneous typing. One of these procedures helps to transform the descriptions of the geological units (granular materials), given in technical paper documents by using a conversational style, into standardized numeric codes. Summary reports, produced in the pdf format, can be generated through decoding and graphic display of the parameters previously entered in the database. MAHA was approved by the national commission for seismic microzonation established by the Italian Prime Minister and, in the next years, it is expected to significantly support the entire process of map production in the urban areas more exposed to seismic hazard.

Introduction

The development of an efficient software system for the storage, retrieval and display of geological subsurface data is a key issue for the production of modern geological and geotechnical maps at all scales (e.g., Howard et al., 2009). During the last decades digital archives of boreholes and other geological and geotechnical data suitable to support the different activities linked with geological surveys have become increasingly available. Some relevant examples are the British onshore borehole collection database (BGS, 2011), the deep borehole collection data of the Italian Geological Survey (ISPRA, 2011), the borehole database of the Department of Primary Industries (2011) of the Victoria State in Australia, and, in more restricted urbanized areas, the web-GIS developed in Seul (Chang and Park, 2004) and in Singapore (Kunapo et al., 2005).

The complexity of the geological nature of the subsoil, the lack of a universally accepted procedure for the description of borehole data, the heterogeneities of both available indirect survey techniques (mainly of geophysical nature) and routine geotechnical analyses are aspects which make the process of digital storage of these data extremely challenging. The challenge becomes even harder when it is necessary to recover large amounts of valuable data of different nature and origin preserved in a number of private archives. In this case, in fact, data migration from paper documentation to digital archives requires facing problems of data homogenization, coding and quality. In addition, data storage also implies the resolution of problems about the correct placement of surveyed data in the geographical space and, at a cognitive level, of their spatial representativeness.

In 2007, the Italian National Department of Civil Protection (NDCP), in close collaboration with the Italian National Research Council (Consiglio Nazionale delle Ricerche—CNR), launched the URBISIT project (http://www.urbisit.it/) devoted to the study of procedures to mitigate and control the risks associated with the geological hazards in the urban areas of the Country. A relevant part of this project was dedicated to setting-up infrastructures to encourage the production of seismic microzonation maps in seismic-prone urbanized areas. According to the Italian guidelines (Gruppo di lavoro MS, 2008), seismic microzonation is a procedure for the evaluation of local seismic hazard which is based on the study of the geotechnical features of the subsoil and on the identification of land sectors (microzones) characterized by homogeneous seismic behaviour and analogous values of potential amplification of seismic waves. A correct approach to these studies relies on the possibility of collecting, analyzing and comparing representative amounts of subsurface data of geological, geophysical and geotechnical nature. Various reasons, linked both to the containment of expenses and to the exploitation of a huge quantity of subsoil knowledge accumulated over many decades of geological and geotechnical surveys which is currently widespread in public and private (professional geologist) archives, fostered the idea to design a database suitable to collect and harmonize these data encouraging, this way, the production of seismic microzonation maps. Such a database has to accommodate a bulk of heterogeneous data that need to be integrated, efficiently elaborated and made ready to be used for an expert evaluation and, possibly, migrated within specifically seismic response modelling software such as SHAKE and its subsequent implementations (Schnabel et al., 1972, Idriss and Sun, 1992).

The strategic importance of seismic microzonation becomes evident when considering that during the last 2500 years Italy was exposed to more than 30.000 earthquakes with an intensity higher than IV–V degree of the Mercalli scale and more than 560 with degree higher than VIII (Gruppo di lavoro CPTI, 2004). Only during the last 40 years the estimated overall economic damage was about EUR 135 billion (source: NDCP). The above mentioned figures characterize Italy as a country with one of the highest ratio in the world (e.g., higher than Japan and California) between seismic risk and energy release from earthquakes (magnitude).

After a three years long preliminary work, a conceptual model of the subsoil, oriented to support seismic microzonation activities, was developed (Caielli et al., 2008) along with the conceptualization of the spatial database and of the whole system for data handling which was called MAHA—acronym for Microzonation And Hazard (Spadoni, 2009, Spadoni et al., 2009). These technical documents have recently been approved by the national commission for seismic microzonation established by the Italian Prime Minister (Gazzetta Ufficiale, 2010) and currently act as the Italian standard for data storage and display in these type of studies (CTMSMS, 2011).

The following chapters describe the overall structure of MAHA and the web-GIS which is on top of the database.