Ground Motion in Areas of Abandoned Mining: A Case Study of PSI Applied to the Northumberland Region of the UK.
Bateson, Luke1; Lawrence, David2; Cigna, Francesca2; McCormack, Harry3; Burren, Richard3
1British Geological Survey, UNITED KINGDOM; 2BGS, UNITED KINGDOM; 3NPA, UNITED KINGDOM
The UK Coal Authority is responsible for all areas of abandoned coal mining and associated subsidence claims in the UK. The scope for radar based ground measurements to assist the Coal Authority with their understanding of ground motions offers an interesting possibility. An Abandoned Mines Advanced Terrain Motion Service was commissioned in the framework of the ESA GMES project Terrafirma to demonstrate the capabilities of Radar Interferometry in such an area.
The Coal Measures form the bedrock for much of the study area in the north east of England. The coalfield has a working history dating back to Roman times. Over twenty coal seams have been mined underground. The working of deeper and deeper coal seams led to the need to pump mine water. All underground mining has now ceased, the majority of mines were closed by the 1980's. Over the past decade there has been a program to turn off the mine water pumps and allow groundwater levels to recover
PSI processing was carried out by FNPA and interpreted by BGS. Two PSI datasets were created; descending ERS from 1995 to 2000 and descending Envisat from 2002 to 2008. Differential InSAR results for the ascending data confirm the descending PSI results
The ERS result shows nine 'hotspots' of subsidence to the south and a larger area of uplift in the north. The subsidence areas show a strong spatial relationship with areas of past mining. However there is a discrepancy in the timing of PSI motions and that of expected subsidence given the type of workings. It is suspected that the motion relates to material extraction, water extraction and the accommodation of resulting motions along faults. Uplift, as seen in the ERS data, in the north has been attributed to the recovery of groundwater levels as mine water pumping has ceased.
The difference between the ERS and Envisat motions is marked; areas which were undergoing subsidence between '95 and '00 are uplifting between '02 and '08. This drastic change is supported by minewater level data which shows that water levels have recovered within this time period, with the resulting increase in hydrostatic pressure accounting for the regional pattern of ground heave.
This presentation will present our understanding of the revealed ground motions and demonstrate how EO can be applied to the problems associated with mining. It will also highlight gaps in our understanding of what is a complex interaction of factors leading to the observed pattern of ground motion