USGS Questions Study's 99.9% Probability of an Earthquake in 3 Years

The US Geological Society is disputing the claims of a recent survey that says there is a 99.9% chance of a 5.0 magnitude earthquake in LA by 2018.

"The 99.9% number -- I don't know the method that was used to derive that,” said Robert Graves, a USGS seismologist and Southern California coordinator for earthquake hazards. “Basically, that's saying that's going to happen. And that level of certainty, to my knowledge, is just not attainable. We can never be that certain.”

Graves is listed as a consultant in the study who helped with calculations.

The USGS even issued a statement, coauthored with NASA’s Jet Propulsion Laboratory in La Cañada Flintridge and recently published in the journal Earth and Space Science, questioning the study and its methods.

Graves says the USGS’s probability for an earthquake over the next three years is 85%.

"The taxpaying public deserves to get quality, reliable information and that's what we're striving to do," Graves said.

The 85% figure was forecast as part of a comprehensive update called the Third Uniform California Earthquake Rupture Forecast, also known as UCERF3, developed by a broad array of scientists over several years.

"I have serious doubts that the conclusions of the paper are supported by the analysis that's presented there," Graves said. In 2014, a 5.1 magnitude earthquake hit La Habra, a city just east of LA, knocking down buildings and displacing people from their homes.

The study's lead author, Jet Propulsion Laboratory principal research scientist Andrea Donnellan, said the 99.9% conclusion should not be viewed as an official forecast and the figure was not the main conclusion of the study.

According to Donnellan the study’s central conclusion was that the deeper layers of the earth did not move during the La Habra earthquake suggesting continued stress on those layers that will eventually need to be released.

"If an earthquake happens in three years, we're both right," Donnellan said.

Scientists were famously wrong when they predicted an earthquake would hit the San Andreas Fault sometime between 1988 and 1993. An earthquake did not arrive until 2004.

"We never said in this paper we were predicting an earthquake. And we said that's the probability of an event," Donnellan said. "There is still a 0.1% chance it won't happen. So we need to test it. And that's what we are doing as scientists."

Graves said the specifics of how scientists came to the 99.9% figure are not fully detailed in the study.

He said earthquakes cannot be predicted in a specific time or place and that seismic research is an "evolving process of eating crow and understanding how little we understand."

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