One woman's quest for geological understanding!

Near Surface Geophysics Group – June 2016 Meeting



The date is looming: On the 16th June 2016, the Near Surface Geophysics Group (NSGG) of the Geological Society of London is holding a NSGG meeting:

“Instrumenting the Countryside – Geophysical Monitoring of the Zone of Human Interaction”


The economic development of the UK’s rural areas goes hand-in-hand with a need to understand the structure of the subsurface. Whether applied to characterise resources – water, minerals, hydrocarbons or geothermal energy – or to mitigate geohazards in the construction of surface and underground infrastructure, the need for continuous monitoring of the subsurface “Zone of Human Interaction” is pressing.

The drive to understand the Zone of Human Interaction has prompted the installation of permanent field laboratories, leading to an unprecedented monitoring capability. The aim of this meeting is to explore and promote recent advances, both academic and industrial, in our national capability to characterise the near-surface environment. Abstracts are invited from all practitioners applying geophysics in fields including, but not limited to:

•    reservoir and repository monitoring
•    groundwater and contaminants
•    geohazards, including landslides & earthquakes
•    ecological conservation.

My abstract submission (poster):

Monitoring subsidence related to relict salt mines using long-term time-lapse microgravity, Marston, Cheshire, UK
Cathrene J. Rowell, Jessica C. Fulton and Jamie K. Pringle
School of Physical Sciences & Geography, Keele University, ST5 5BG

The UK Permo-Triassic red beds host evaporates which can be commercially exploited. The Cheshire Basin, an asymmetrical half-graben formed by the rapid subsidence of a segment of the Permo-Triassic rift system, contains >4.5km of Permo-Triassic red beds, including the Mercia Mudstone Group which accumulated in playa and tidal-flat environments. The Mercia Mudstone Group is the host to two major halite formations: The Northwich and Wilkesley Halite formations.

Both brine and salt has been extracted from mainly two workable horizons of the Northwich Halite Formation in the Cheshire Basin in various locations, and rock salt is still mined in Winsford. Surface subsidence as a result of salt mining and brine pumping in Northwich, and the surrounding areas in Cheshire, has occurred throughout history.  This has varied in severity, with evidence of subsidence ranging from topographic depressions to catastrophic surface collapse.

In order to detect, characterise and monitor areas susceptible of subsidence, a combination of remote sensing and near-surface geophysics can be applied. A section of the Trent and Mersey Canal, in Marston (Northwich), crossing 3 abandoned salt mines, in close proximity to others and in addition to areas of previous subsidence, has been the focus of long-term microgravity surveys for over a decade.  The data collected over this period shows consistent, deepening negative anomalies at the margin between the Adelaide and Old Marston relict mine workings, as opposed to over the mines themselves.  By correlating microgravity data with topographic data of the site, 2D gravity models have been produced: the anomalies are interpreted as upwardly propagating voids, and associated collapse material.  A void feature at the point of the microgravity excursion has been confirmed by intrusive investigations, and investigation of canal water and the underlying silt accumulation on the canal floor has been undertaken in order to ascertain any connection to underlying mines and potential canal collapse.

Watch this space!

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