2008 and (mouse over) 2014 USGS maps of peak ground acceleration for 2-percent probability of exceedance in 50 years and VS30 site condition of 760 meters per second.
This morning I’m looking at the United States Geological Service’s report: Documentation for the 2014 Update of the United States National Seismic Hazard Maps and the first bit that caught my eye was a change to the 2014 map (mouse over the image above to view) to include areas where suspected nontectonic earthquakes have been deleted.
According the report (page 32), the USGS maintains:
a manually edited, “special-case” catalog of suspected erroneous or nontectonic events (explosions, mining-related events, etc.) identified from special studies. For the 2014 update, nontectonic events compiled by the CEUS–SSCn are added to this file. These special-case events are deleted from the final catalog.
Locally, notice the deleted section in Northeastern Ohio. What nontectonic event have we experienced in that area marked as deleted?
Earlier this year, Reddit Los Angeles hosted an Ask Me Anything with Dr. Lucy Jones, USGS Seismologist and Science Adviser on Seismic Safety to LA Mayor Eric Garcetti. During that session, fracking entered the discussion when a participant asked Dr. Jones:
stewie2552: How seriously are you taking the fracking debate? There’s a lot of controversy with it, and I know just recently the USGS is increasing its research into it as a source for earthquake activity. I’m not from the area so I’m unaware how much fracking actually occurs in California, but is it a concern for you and your office? I’m not really sure where I stand on the issue, but would love your input.
Jones: Fracking itself does not cause earthquakes – it is happening at shallow depths and the earthquakes begin farther down. However, after fracking, there is a noxious brew of water and chemicals that must be disposed of, and they generally pump it deep into the earth to get it below the water table. That is setting off earthquakes on the East Coast where the rate of M equal-to-or-greater-than 3 earthquakes has increased from 23/yr to 200+/yr. [Emphasis mine, JH]
It is not clear how much fracking is happening in California. The oil companies report how much oil they extract from the ground but not the techniques they use to get it.
It’s hard to be sure whether earthquakes in California have been affected by oil extraction. We were pumping oil before we started recording earthquakes, so we don’t have a baseline.
Allow me to be clear. I do not believe that the USGS is covering up these earthquakes (there are plenty of others who see conspiracies here, particularly as reporting pertains to the super volcano under Yellowstone National Park, but I’m not one of them) but rather see these marked areas as a way that the USGS is actually high-lighting these events.