There have been a couple of reported earthquakes that have since been removed from the database. This happens when seismic waves are incorrectly interpreted by the computers, typically from the results of larger magnitude earthquakes. These large magnitude earthquakes can produce seismic waves that are easily interpreted to be local earthquakes in other locations. When people review the data, these errors are omitted. However, the phantom earthquakes are often submitted to the earthquake notification system prior to this removal. These deletions raise angst in the conspiracy theorists’ minds (we can only imagine what actually is in their minds, if much at all), suggesting that there is some global conspiracy to hide seismic data, for some nefarious reason. I cannot think of a single reason why someone might want to hide seismic data (well, maybe for nuclear testing). It would be difficult to really hide seismic data because there are so many unique and independent seismic networks, which publish their data online.
Sign up for the Earthquake Notification System here.
The USGS has posted information about these recent Phantom Earthquakes and the reasons behind their deletions. I paste the relevant information below, just in case there is a conspiracy that will later remove these words from the internets [sarcasm].
Here was the page for the M 5.1 Lewiston earthquake, which was the result of seismic waves travelling from the M 6.7 earthquake along the Alaska Peninsula. This is my first post about the M 6.7 earthquake and here is a post that I wrote that includes animations of historic seismicity in the region.
Here was my post about this earthquake. This happened at a time when I needed to go to sleep, so I was putting off from posting a more detailed accounting until the next day. Of course, when I awoke the next day, it was deleted… So I had little to post about. This is the link to the USGS for this earthquake.
This is the pager alert (which is also an automated product):
Here is the “Did You Feel It?” map, with no reports (should be no surprise, since there was no earthquake).
Here is the Modified Mercalli Intensity shake map, showing that people would have felt it if it had happened (and probably would have reported it!).
Here is what the USGS states about these earthquakes:
Commentary for Multiple “Phantom Events” in California – posted June 2, 2015
Automated notification systems are a convenient and often essential component of modern life. The USGS has invested heavily in developing automated systems that provide the public with timely and accurate earthquake information. On rare occasions the Earth throws a curveball and on May 29th and 30th, the USGS issued multiple alerts for false earthquakes in Northern California. The first, a M5.1 near Lewiston, CA, was distributed on Friday. More false alerts were distributed on Saturday, including a M5.5 near Ukiah and M4.7 near San Simeon.
These erroneous earthquake notifications were created by the seismic waves from large, distant earthquakes. On Friday, a M6.7 earthquake occurred at a depth of approximately 60 km, 111 km off of Chirikof Island, Alaska. It was this earthquake that fooled the automatic processing of the Northern California Seismic System to issue the first false alert. Just 28 hours later, a M7.8 earthquake off of Japan with a depth of more than 660 km – the deepest earthquake of its size to have occurred during our history of recording – spawned two more phantom events in Northern California.
Large earthquakes have created challenges for regional seismic monitoring in the past. This problem is particularly acute for deep earthquakes as they generate very impulsive seismic waves which may be misinterpreted as a local earthquake. The USGS and its partners have developed a number of methods to stop or screen these events from being distributed on the Web and through such mechanisms as the Earthquake Notification Service. The USGS will be implementing changes to improve the system and minimize the chances of this occurring in the future.
The erroneous events were deleted quickly by a duty seismologist. Unfortunately, a problem with the distribution software prevented the delete messages from being transmitted to recipients of the Earthquake Notification Service. The inability to transmit the information about the false events to the users of the Earthquake Notification Service caused significant confusion and the USGS regrets the problems caused by this failure. USGS staff have identified the problem in the distribution software and fixed it.
Errata for “Phantom Events” in Central and Northern California resulting from the M6.7 Alaska Earthquake on 2015-05-29 07:00:29 UTC
Strong earthquakes generate seismic waves that spread across the entire globe. When the earthquakes are deep, the distant recordings are quite impulsive and are often mistakenly identified by automated systems as local earthquakes. On 2015/05/29 07:00 UTC, a 60 km-deep M6.7 earthquake occurred offshore of Chirikof Island, Alaska and swept across the seismic networks in northern California. The automatic earthquake detection systems recognized the arrival of seismic energy but misinterpreted it as several earthquakes, including an M 5.1 event occurring near Lewiston, rather than one large distant event. These “phantom events” were automatically released for public distribution on the Web and through the Earthquake Notification Service. All “phantom events” were cancelled by the duty seismologist within 15 minutes.