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Pebble Partnership's quake data lacking

  • Author:
  • Updated: September 27, 2016
  • Published April 21, 2012

Ken Taylor, the outgoing vice president of environment for the Pebble Partnership, invited Alaskans to read their recently released Environmental Baseline Document (EBD) in a Compass piece dated March 16. He encouraged citizens worried about Pebble to dive into its 30,800 pages. The document doesn't describe mine plans, so it's unclear how it would alleviate concerns about mine development. But I dove in nonetheless, focusing on their analysis of earthquake risk.

I was actually quite excited to read this document. I'm a geologist specializing in geologic hazards like earthquakes and tsunamis. A year ago, Mr. Taylor promised me the EBD would include a detailed analysis of earthquake risk, incorporating new data from Pebble's own studies.

Southwest Alaska, like much of the Pacific Rim, is a seismically active and geologically complicated place. But while geologists have scoured places like Japan and California, faults in rural Alaska are not well studied. For example, the Lake Clark Fault's trajectory relative to the Pebble prospect is unknown.

With access to millions of dollars and specialized survey equipment, I was hopeful that Pebble's scientists could expand this knowledge.

As it turns out, only seven pages out of 30,800 were dedicated to earthquake risk. No new science. They rely only on a handful of previous studies, none of which pinpoint the location of the Lake Clark Fault where it passes near Pebble, or determine whether the fault might produce large earthquakes. Other developers pursue a much higher standard in planning for seismic risk. For example, the Alaska Pipeline Project put millions of dollars into research on earthquakes along their pipeline route.

Pebble's conclusions based on these references? Earthquake risk at Pebble is "not considered to be significant." But the logic used to draw this conclusion is rife with contradictions and faulty assumptions.

Pebble argues there is no evidence of earthquakes on the Lake Clark Fault. A lack of knowledge is not proof the fault isn't active.

Pebble argues that rocks near the prospect are so strong that faults wouldn't break them. But Pebble's own geologic map of the prospect (Chapter 3 of the EBD) charts many small faults.

Pebble implies that faults follow glaciers, so the Lake Clark Fault likely deviates around the mine site, as ice-age glaciers did. But examples across Alaska and elsewhere, including the Lake Clark Fault, show faults can cut right across glacial flow.

These latter two flawed arguments are their basis for concluding that the Lake Clark Fault abruptly veers from its nearly straight path toward the heart of the Pebble prospect.

Getting these details right really matters. Mine facilities and tailings dams are built to a certain engineering standard -- designed to withstand an earthquake with a particular strength and location. If this is miscalculated, a tailings dam could fail, flooding downstream waters with potentially billions of tons of toxic waste.

If these seven pages contain bad science on such a critical issue as earthquake risk, what about the other 30,793?

If you want to convince me that Pebble faces no earthquake threat, I have some suggestions:

• Use the best bedrock mapping techniques (e.g. aeromagnetics) to extend the mapped trace of the Lake Clark Fault well beyond Pebble.

• Conduct a high-quality LIDAR (light detection and ranging) survey of any possible paths for the fault, and also of elevated shorelines along Lake Clark and Lake Iliamna.

• Find experts with a proven record of finding and establishing the activity of faults to do fieldwork and analyze the data.

And make the data and results available so that I can convince myself the prospect truly sits in a tectonic sanctuary far from the raucous geology that typifies Alaska.

Bretwood Higman lives in Seldovia and is executive director of the nonprofit Ground Truth Trekking. He has a doctorate in earth and space sciences from the University of Washington and is conducting studies of possible seismic hazards near the Pebble mine prospect.


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