| Title | IRETHERM: Multidimensional Geophysical Modelling of the Southern Margin of the Dublin Basin |
|---|---|
| Authors | Jan VOZAR, Alan G. JONES, Volker RATH Joan CAMPANYA, Sarah BLAKE, Robert DELHAYE, Thomas FARRELL, Riccardo PASQUALI |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | geothermal energy, Ireland, magnetotellurics, seismic reflection |
| Abstract | We present multi-dimensional magnetotelluric (MT) modelling of the MT data collected in the Newcastle area in the frame of the IRETHERM project (www.iretherm.ie) to develop a strategic and holistic understanding of Ireland's geothermal energy potential through integrated modelling of new and existing geophysical, geochemical and geological data. The Newcastle area is situated on the southern margin of the Dublin Basin. A description of data processing methods, 2D and 3D geoelectrical models of the area and integrated modelling with other geophysical data are presented here. The MT soundings were carried out in the highly urbanized Dublin suburb in 2011 and 2012. The MT data were heavily noise-contaminated and distorted due to electromagnetic noise from nearby industry and DC tram/railway system; processing using several robust codes to were able to obtain reliable and interpretable MT impedance and geomagnetic transfer functions. The most “quiet” 4-hour subsets of data during the night time were used in multi-site and multi-variate processing, with the most reliable sounding curves spanning the frequency range 10 kHz to 0.001 Hz. A new novelty technique using inter-station transfer functions has been implemented as a processing tool to get broader primary data for final multi-dimensional modelling. In order to reduce galvanic distortion in the MT data, the regional 2-D strike direction must be determined. Tensor decomposition was applied at each site to determine if the data are suitable for 2D modelling. The final 2-D models underwent examination using a new stability technique, and the final two 2-D profiles with reliability estimations, expressed through conductance and resistivity, were prepared. As a concluding of the modelling, 3-D models of all MT data in the Newcastle area have been prepared and further on-going 3D modelling along with inter-station magnetic transfer functions have been prepared. The integrated modeling with existing seismic reflection profiles and gravity data in the area reveals that the Blackrock to Newcastle Fault (BNF) is visible in the models as a conductive area to depths of 4 km and is highly fractured. Generally, the southern area is more resistive and compact with a horizontal conductive layer at a approximately 1 km depth, with a very thin sedimentary layer on top. The structures north of the BNF are more heterogeneous, with deeper conductive layers (2-3 km) and thicker (several hundred metres) sedimentary layers above. In the next phase the MT data with both gravity and seismic data, which have been collected in the area since August 2013, will be inverted, which will greatly improve the spatial resolution of subsurface models and estimations of their physical properties. |