T57 Utilizing 2-D and 3-D Near-Surface Geophysics to Generate Improved Surface and Subsurface Geologic Maps

Sunday, 1 November 2015
1:30 PM - 5:30 PM
Room 322/323

SEMI-AUTOMATIC 3D-MODELLING OF LARGE AEM-DATASET, A CASE STUDY FROM A SKYTEM SURVEY IN SWEDEN

Paper number: T57-14
Program: Technical Sessions
Time: 4:45 PM – 5:00 PM

Authors

Abstract

In 2013 the Geological Survey of Sweden (SGU) conducted a 540 km2, airborne transient electromagnetic survey (ATEM) on the island of Gotland situated in the Baltic Sea 100 km from the mainland of Sweden. The focus of the study was hydrogeological, and the main purpose to find and delimit new groundwater resources, and to map the depth to the interface between fresh and saline groundwater.

The translation of these large data sets into geological models is a time-consuming task. In order to reduce the effort the ERGO (Effective high-resolution Geological Modelling) project has developed a software system (Smart Interpretation – SI) which uses automated methods to design geological 3D models. In short, the software is taught how to interpret data in one area by the researcher after which the program can automatically use this knowledge in other areas to produce a geological model.

The sedimentary rock sequence on the island of Gotland is 250-700m thick and has a dip of 0.3 degrees to the southeast. Simplified, the sequence can be seen as a layer cake and the uppermost 200m, which may be of interest for drinking water aquifers, consists of limestone and marlstone alterations.

We applied the developed SI algorithm to develop a 3D geological model on parts of Gotland based on the SkyTEM data. This enabled us to produce a model much more efficiently compared to traditionally used routines. The software was also able to propose solutions to geological interpretations of the AEM data that otherwise would have been either difficult or very time-consuming to model. The methodology, however, is not able to fully account for other data like for instance lithological data and chemical data, so the use still has to be combined with a certain degree of cognitive co-interpretation, where all expert knowledge are utilized.

The results and 3D models from this study will then be compared to results from a new SkyTEM survey performed in September 2015 in new areas on the island of Gotland.