Numerous media outlets have repeated the headline that seem to say a USGS scientist, Tom Brocher, has predicted there will be a major quake in San Francisco in the next few days, as seen on the left of the above image.
However, Tom Brocher responded to this by saying "my comments have been misrepresented" and that the actual risk is "a 31% probability of a magnitude 6.7 or larger event in the next 30 years". And the USGS spokeswoman said: "the USGS is not predicting an earthquake 'any day now'"
In other words there's no prediction, just a one in three chance of a large quake some time in the next 30 years. Nothing like "any day now".
The phrase "any day now" was only spoken by the reporter Andria Borba. Brocher is simply noting that earthquakes can happen at any time, so it's good to be prepared.
The USGS later issued an update on their Facebook page:
Here's what Brocher actually said in the article:Although a Hayward fault quake CAN happen at any time, it does NOT mean it’s "expected any day now.” Misquotes in one story have gone viral. USGS does not predict quakes. The M4 quake in Fremont, Calif. on Tuesday was not likely to have much of an impact one way or the other on the likelihood of a major earthquake occurring on the same fault. Good reminder to prepare.
The "140 years" comes from the historical record:“The past five major earthquakes on the fault have been about 140 years apart, and now we’re 147 years from that 1868 earthquake, so we definitely feel that could happen any time”
So we've just got four data points here. The intervals of 155, 160, 95, and 143 years.Earlier earthquakes have been detected by trench exposure and associated carbon dating. Combined with the historic record, the last five major events were in 1315, 1470, 1630, 1725, and 1868, which have intervals of about 140 years (note that 2008 is 140 years from the major 1868 event).
What this indicates is not that earthquakes happen on this fault "every 140 years", but rather that they can happen at any time.
Brocher also noted
So while earthquakes can happen at any time, and it's a good idea to be prepared, there's nothing at all to indicate a large quake will happen "any day now". It could be tomorrow. It could be in ten or a hundred years. So get your earthquake kit ready just out of normal caution, not media hysteria."Tuesday morning’s 4.0 earthquake was not likely to have much of an impact one way or the other on the likelihood of a major earthquake occurring on the same fault."
I contacted Tom Brocher, and he gave a detailed clarification:
And the original source of the story, the Bay City News wire service, has been contacted by the USGS, leading to then issuing this this advisory:
You are correct in thinking that my comments were misrepresented.
The USGS asked the Bay City News to print a clarification which I have pasted at the end of this response. There was a misunderstanding between the words "could" and "will". The Hayward fault is capable of producing a major earthquake at any time, but there is currently no scientific basis for making a prediction for when that earthquake will occur. The Uniform California Earthquake Rupture Forecast (UCERF3) model gives a 31% probability of a magnitude 6.7 or larger event in the next 30 years on the Hayward-Rodgers Creek fault system.
As the attached fact sheet about the Hayward fault states, geologic studies at Tule Pond (in Fremont) on the southern end of the Hayward fault have shown that the average interval between the past 5 surface-rupturing earthquakes has been 140 plus or minus 50 years. The average interval of the past 11 earthquakes on this segment of the fault is 170 plus or minus 80 years.
The last surface rupturing earthquake on the Hayward fault was October 21, 1868: it had an estimated magnitude of 6.8.
The U.S. Geological Survey would like to clarify the comments of one of its scientists today in BCN29 (FREMONT QUAKE). Spokeswoman Leslie Gordon says although an earthquake can happen at any time, the USGS is not predicting an earthquake "any day now."
Although Bay City News Service stands by its report, subscribers may want to consider using the following alternate lede to BCN29:
X X X Although the fault that produced a 4.0-magnitude earthquake in Fremont this morning is not expected to change the likelihood of another major quake on the same fault, a U.S. Geological Survey scientist said a major earthquake could happen at any time and residents should be prepared.