Errata for Latest Earthquakes

Beginning in 2010, we will post information here regarding errors in the Real-time Earthquake system that led to erroneous information getting posted on the website or distributed.

The USGS and networks contributing to the Advance National Seismic System (ANSS) take great effort to provide accurate and timely earthquake information.  Occasionally our systems produce erroneous information that is released to the public via our web pages or Earthquake Notification System. These mistakes are generally promptly identified by seismologists, removed from our web pages, and “delete” e-mails are sent through ENS. In the interest of rapidly providing earthquake information to the public, most of the information about earthquakes that occur in the USA is automatically posted to the web and ENS if it meets quality standards. There is a trade-off between the speed of our earthquake notifications and number of false alarms in the same way that any kind of "breaking news" story may have substantial changes or corrections as more information is received. The faster we release earthquake locations and magnitudes, the more likely it is that the information may be erroneous. Experience demonstrates that imposing more restrictive quality standards prevents the release of legitimate earthquake information. Here we document serious errors that have resulted in the distribution of flawed information to response organizations and the public. Hopefully this discussion will provide our users with a better understanding of our system.

2012

Errata for "Phantom Events" in Central and Northern California resulting from the M7.7 Sea of Okhotsk Earthquake on 2012-08-14 02:59:42 UTC.

Strong earthquakes generate seismic waves that spread across the entire globe. When the earthquakes are very deep, the distant recordings are quite impulsive and are often mistakenly identified by automated systems as local earthquakes. On 2012/03/20 18:02 UTC a 626km-deep M7.7 Earthquake occurred offshore of Poronaysk, Russia and swept across the seismic network in northern California (NCSN). The automatic earthquake detection systems recognized the arrival of seismic energy but misinterpreted it as 3 M 5.1 events occurring near King City, San Martin, and Chico, 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 3 events were cancelled by the duty seismologist within 12 minutes.

Errata for "Phantom Event" offshore of Northern California resulting from the M5.9 Blanco Fracture Zone Earthquake on 2012/04/11 22:41 UTC.

An earthquake occurred offshore of Oregon at 43.59 -127.56 with a magnitude of 5.9. The earthquake was reported to the USGS recenteqs website by the Alaska Tsunami Warning Center at 22:46:57. The Northern CA Seismic Network (NCSN) also detected the earthquake with its automated software, but mislocated the earthquake because it occurred outside the network of seismic stations monitored by the NCSN. The erroneous NCSN location was posted to the recenteqs website at 22:46:46 UTC with Ml 3.9 and coordinates 39.36 N, 124.05 W. Because the mislocation was more than 100km from the ATWC location, both solutions were displayed on the web.

The NCSN automated system then updated the Ml magnitude with an Mw of 5.34 at 22:50:17 UTC, which underestimated the event magnitude because of the incorrect location. The NCSN duty seismologist responded at 22:53:34 UTC, but didnŐt recognize that the NCSN information was a mislocation of the Blanco Fracture Zone event. Consequently, instead of deleting the incorrect information, the duty seismologist issued a reviewed version of information, but with the previous ML value. The mistake was quickly recognized, and the event was deleted at 23:04:20 UTC.

Errata for "Phantom Events" in Southern California resulting from the M7.4 Mexico Earthquake on 2012/03/20 18:02 UTC.

Strong earthquakes generate seismic waves that spread across the entire globe. As the seismic waves generated by the M7.4 Earthquake near Ometepec, Mexico on 2012/03/20 18:02 UTC swept across the seismic network in southern California (SCSN) the automatic earthquake detection systems recognized the arrival of seismic energy but misinterpreted it as six local events rather than one large distant event. Three of these "phantom events" were of sufficient quality to be automatically released for public distribution. All were cancelled by analysts within 5 minutes. In addition an explosion occurred as part of quarrying operations in eastern San Diego County as the distant earthquake waves passed. Such quarry explosions are common in California. This event was correctly detected and located by the SCSN but an incorrect magnitude (M4.2) was calculated because of the coincidence of high amplitude waves from the Mexican quake.

2011

Errata for Temporary Deletion of Earthquake Information for Magnitude 3.5 San Leandro, California on 2011 August 24 16:57:44 UTC

The Northern California Seismic System located a magnitude (M)3.5 earthquake 5 km from San Leandro on 2011 August 24 16:57:44 UTC. Automated event processing was normal. A preliminary automatic solution with a ML3.6 was available 3 minutes, 40 seconds after the origin and was distributed via the USGS Earthquake Notification System (ENS). Initial seismologist review and confirmation occurred at 17:19 UTC. At 17:44 an update was released with an Mw3.5. Other products including ShakeMap and Did-You-Feel-It, and mechanisms were also properly generated. At 20:19 an analyst performing routine data review accidentally deleted the event. This error caused the issuance of a "delete" message from the ENS to all subscribers who received the original notification of the event. Restoration of web information occurred at ~20:58 UTC.

ENS logic prevents issuing of updates to subscribers unless there is a significant change in the event magnitude. In this instance, identical information was re-posted to the web, so no subsequent ENS message was issued to ENS subscribers. We regret that our systems were unable to issue a correction through ENS and apologize for any confusion that resulted.

Errata for ANSS/NEIC double posting of Arkansas Earthquake Feb. 17, 2011

A minor earthquake occurred on February 17th at 10:49 UTC (4:49 AM at the epicenter) 4 miles from Guy, Arkansas. Eleven minutes after the earthquake, the Advanced National Seismic System (ANSS) released an initial location and preliminary magnitude of 4.0 for the earthquake. Forty-two minutes after the earthquake, a software problem resulted in a double posting of the same earthquake with an incorrect magnitude of 4.7. These errant postings were removed within 16 minutes. The earthquake was updated to a refined magnitude of 3.8 an hour after the event.

The release and double posting of the magnitude 4.7 event was an error. However, magnitude updates (in this case from a preliminary magnitude of 4.0 to its current magnitude of 3.8) are standard procedure. Magnitudes are often updated as more data become available and time-intensive human analysis is conducted on the seismograms.

Errata for UUSS False Alarms of Feb. 11 & 12, 2011

Over the course of approximately two days, February 11 and 12, 2011, the automatic seismic processing software of the University of Utah Seismograph Stations (UUSS) reported a large number of earthquakes occurring across the Yellowstone region. The overwhelming majority of these reports were false alarms, caused by malfunctioning telemetry equipment. This includes the report of an M 4.6 earthquake on Friday, February 11 with an origin time of 7:36 pm (MST). The automated report of this event was broadcast at approximately 7:40 pm (MST), and within four minutes, at 7:43 pm (MST), a seismic analyst had reviewed the report, determined it was a false alarm, and sent delete requests to the UUSS and USGS/NEIC web pages.

Although the automatic seismic processing system used by UUSS is enormously useful, it is not sophisticated enough to produce robust, definitive results without human oversight. Earthquake reports posted to UUSS and USGS web pages should be viewed cautiously if they are labeled as automatic reports, i.e. not labeled as having been reviewed by a seismologist. UUSS technical personnel are currently working to address the Yellowstone telemetry problem, but more false alarms are possible until the problem is fixed.

See additional information on the Volcano Hazards Program-Yellowstone Observatory website.

2010

Errata for UUSS False Alarm of August 4, 2010

On Wednesday, August 4 shortly after 6:00 pm (MST) the automatic seismic processing software of the University of Utah Seismograph Stations (UUSS) reported the occurrence of a magnitude 4.1 earthquake in northern Utah. The nominal origin time was 6:04 pm with an epicenter of 41.8 N 112.1 W. This information was automatically posted to the UUSS and USGS web sites. Within approximately 10 minutes of this automatic alert, UUSS staff seismologists had reviewed the relevant data and determined that it was in fact a false alarm, and that no earthquake had occurred in northern Utah. Subsequently, the event was “cancelled” and removed from the web pages.

The false alarm was created by a magnitude 3 foreshock that occurred 14 seconds prior to a magnitude 4.8 earthquake that occurred near Jackson, Wyoming at 6:04 pm (MST). The UUSS automatic processing software was confused by the combination of seismic waves from these two earthquakes and inadvertently created the fictitious Utah earthquake. Although the automatic seismic processing system is enormously useful, it is not currently sophisticated enough to always produce robust, definitive results without human oversight.

Errata for UUSS False Alarm of August 18, 2010

On Wednesday, August 18 shortly after 6:50 am (MDT) the automatic seismic processing software of the University of Utah Seismograph Stations (UUSS) reported the occurrence of two nearly simultaneous events: one event near Cedar City, UT (MC 4.1, ML 3.3), with approximate coordinates of 37.63 N 113.24 W, and a second event in the mining region of Utah (MC 3.5, ML 3.0) with approximate coordinates of 38.97 N 111.59 W. Within approximately 15 minutes, a UUSS staff member reviewed the second of these events and confirmed it as a true seismic event. A second staff member reviewing the other automatic detection (near Cedar City) determined that it was in fact two events: a magnitude 3.0 foreshock followed by a magnitude 3.8 main-shock, both in the Cedar City area. The two staff members were in communication, and soon determined that the initially confirmed event in the mining region of Utah was in fact a false alarm created by the automatic seismic processing software. It was officially cancelled.

In summary, UUSS detected and located two seismic events in the Cedar City region (Event IDs uu08181251 and uu08181252). The main event (ML 3.8) was located within approximately 45 minutes of origin time and a press release was issued. At that same time, UUSS mistakenly confirmed a false alarm event (Event ID uu00007301), before canceling it approximately 35 minutes later. Although the automatic seismic processing system used by UUSS is enormously useful, it is not currently sophisticated enough to always produce robust, definitive results and can occasionally generate misleading information.