I THINK MINING

A 5.7 earthquake has just rattled the building here in Santiago where I sit.  This link tells us the magnitude, location, and depth—a real deep 95km.

I was sort of day-dreaming my way through compilation of a PowerPoint presentation, when the computer started to shake and I heard the noise of the windows and screens.  My chair wobbled back and forth a bit.  Nothing much I concluded and set to work again.   Then about thirty seconds later the main event hit:  now the whole building, walls, floors, windows, and occupants were amoving and agroaning.   The noise of the building as it swayed was almost more impressive than the physical movement itself.  Not a long shake.  I barely had time to stand up and join the stream of people heading for the foyer, and all was still again.

No discernable damage to the building that I can see.  The elevators are out of service “for inspection.”  And everybody is back at work.

This earthquake reminded me to note the materials at this link on the 27 February 2010 Maule earthquake that did cause damage in Chile.  The reports at the link include masses of information that is well worth while taking time to download and read. 

I have downloaded the report on the response of tailings facilities to the earthquake.  Generally not much impact on the embankments or “muro” as it is called here in Spanish.  What I found most interesting were reports of sand boils and large slumping or settlement of the finer tailings discharged behind the outer walls. 

I am in a debate right now on this issue.  I cannot prove it, but I have intellectual backing from the sharpest minds on the topic that I know.  I believe that there is a possibility that in the right earthquake the tailings in the reservoir could flatten to a near zero slope.  Everybody here tells me that I am wrong. 

“It did not happen in 201o and has not happened before that,” they say.

Andy Fourie in his presentation at Paste 2012 noted that no paste or thickened tailings facilities has yet been hit by an earthquake that could result in beach flattening–but, he warns, it could happen.   We just do not know.  Another Black Swan waiting to glide upstream I suspect. 

I am not aware of any CPT investigations into paste and/or thickened deposits sufficient to measure the liquefaction potential of the tailings.  So if you know of any, please share the information with all of us.

Meanwhile, I would prefer a conservative approach–make the starter dike and subsequent rising dam sufficiently high to deal with potential earthquake-induced flattening of the tailings in the reservoir.  I am told it happened some years ago at a tailings facility in central America.  It is, in my opinion, entirely possible it could happen in South America.