BULGA-INLET FAULT LINE

 

 

 

 

 

NSW Department of Lands produced an aerial photograph of Howes Valley (see below) on 11. July, 1971. One of the local residents of the Bulga Inlet valley, Paul Jessop (now deceised) become interested and obtained several copies of this earial photograph.


 

The photographs shows the mountains of the Wollemi National Park at the top and the Wollombi Brook valley at the bottom. Bulga Inlet is in the center of the photograph and the Bulga village is located below at the bank of the Wollombi Brook.

What sparked Paul's attention was a line that goes from the lef hand bottom corner, where the little cloud sits, going diagonnally in about 2 o' clock direction. It takes a while to pick it up first time but subsequently the line becomes unimstakable. With the benefit of the advice of some of his family with a geological bacground, Paul interpreted this feature as an old geological fault line He believed that there may be a huge aquifer of fresh water stored in the fault line substrata. Paul liked to talk about the fault line and to show it to anybody who was interested. Many residents of The Inlet probably already know about it.

The fault line becomes visible in the mountains over Milbrodale (see the litle whit cloud) and then crosses the Putty Road at Milbrodale, then crosses the Parsons Creek and Thompson Road. On crossing the Whybrow mountains area it becomes very clearly visible until it disappears while disecting The Inlet valley smack in the middle. The fault then crosses the mountain above Wambo, intersects the Wambo Creek and finally disappears in the escarpment above Wambo Mines near Warkwarth.

The Bulga-Inlet fault line is even better visible on the recent satellite photograps on Google Earth.

 


 


 

The northern entry of the fault line into the Bulga-Inlet can be seen as a gorge crossing the clifs of the sandstone escarpment. It contains an ephemeral waterfall that runs during the wet season. The sandstone cliffs show several clear deep vertical cracks but these appear to be quite old.


 

The southern entry of the faultline into the Bulga Inlet is a bigger gorge but not so steep as the northern site. It also contains an ephemeral stream and, more importantly, forest road to California in the Wollemi National Park.


 

In general, the Bulga Inlet valley is quite densly populated and several houses, including Paul Jessop's are located right on the fault line.


In May to September, 2007 Sydney Gas Limited drilled exploration Core Hole 3 <>>>>ref > on this property as a part of their Hunter Exploration Coal Bed Methane Gas project. The drilling platform was located about 250 metres west from the fault line. The following picture shows the exploration drill in the position with the fault line northern gorge in the background. There was no indication that the core hole intersected Paul's large reservoir of fresh water stored in the fault.


Sydney Gas drilling rig at Core Hole 3, northern entry into the faultline is behind the dead tree

 

Syney Gas drilling rig, southern fault line gorge is in the top lef hand corner

 

What are the consequences of living on a geological fault line?

Wikipedia, the free ecyclopedia, defines "fault line, is a planar rock fracture which shows evidence of relative movement". It shows some amazing examples of various famous fault lines.

The comfort of living on a fault line depends very much if the fault line is active OR inactive. Active faults are often associated with earthquakes! Fortunately from the level of errosion, soil formation and vegetation cover, the Bulga-Inlet fault line must be quite old and looks inactive. An active fault line looks like this:

 


An active fault line in Tennessee, USA. Note how the crop rows have shifted since planting.

 

This is certainly not the case in The Inlet, we have never seen anything like it. However, Hunter Valley has several ative fault systems. For example, the Hunter Mooki Thrust Zone starts near Maitland. The Hunter River Cross Fault and the Newcastle Fault Line were implicated (http://www.ga.gov.au/image_cache/GA4190.pdf) in the 1989 Newcastle Earthquake. Interestingly, in the first reports of the Newcastle earthquake on the ABC radio the seismologists put the epicentrum of the quake as "near Putty" and talked about a fault that links Putty to Newcastle. We now know that the epicentrum was in fact directly under Boolaroo.

Fault lines by their very nature are associated with vertical cracks and fissures in the underlying rock layers.These fissures can be open, part-open or closed by geological processes. The following sketch explains this situation as pertinent to the coal or gas mining.


Schematic crosssection of a tectonically disturbed area with coal seams, with an indication of the undisturbed overburden sediments

If the vertical cracks are open and the natural hydrology of the fault line is disturbed, then they can act as a conduit for water or gas in both up or down directions. Water or gas can move between various coal measures or even between coal measures and the surface. Thus, if the gas company, such as in our case Sydney Gas, extracts water from a coal seam in order to obtain coal bed methane (see here for review of technological details) and if free vertical cracks are present in the geological strata, then the water from the surface aquifers may drain back into the target coal seam. To put it plainly, the surface aquifers associated with the Wollombi Brook may be damaged. Similarly, coal bed methane, once released from the coal matrics, may travel trough the vertical cracks intu the surface layers where it is definitively not wanted. There is no way to know beforehand where such vertical cracks in the coal bearing strata exist. You cannot prove by science that something does not exists! The only safeguard that the gas mining companies have is to keep well away from the streams and fault lines. Australian Rivers SOS suggest at least a one kilometre buffer zone. What a sane suggestion!