June 14, 2005: A Case Study in Tsunami Warning and Response
At 7:51 PDT (0251 UTC) on June 14, 2005, an earthquake occurred 90 miles northwest of Eureka, California, that was felt in communities in both California and southern Oregon. The preliminary magnitude of the earthquake was M7.4 and the location was within the Gorda Plate. Within five minutes, the West Coast/Alaska Tsunami Warning Center (WC/ATWC),1 in conformance with established procedures, issued a tsunami warning for the coastal areas from the California-Mexico border to the northern tip of Vancouver Island, British Columbia. Before the warning was issued, the intensity and duration of the earthquake shaking in Humboldt and Del Norte counties provided the first “unofficial notification” to residents of northern California and southern Oregon of a possible tsunami triggered by an earthquake.
TWO WARNINGS FROM THE TWCS
Although no WC/ATWC staff were in the center facility at the time of the earthquake, within a few minutes after the earthquake TWC staff were at their stations, had assessed the seismic data, and delivered a warning message to its area of responsibility (AOR) regarding possibility for tsunami waves forming in response to the earthquake tremors. As noted above, the earthquake provided the initial notification of the potential for a tsunami to local residents, resulting in local individual actions well before the official warning was received and disseminated by local governments. At 7:59 PDT (0259 UTC), the Pacific Tsunami Warning Center (PTWC) in Hawaii issued a Bulletin for its AOR (including Mexico) stating that there was no tsunami warning in effect (for its AOR). Although the two seemingly contradictory notifications were both correct, state and local officials who received both were left with the impression that the initial notification was canceled. Officials in southern California were faced with the potential of a locally damaging tsunami striking San Diego county that would not impact Tijuana, Baja California, a few miles to the south.
By 8:19 PM, after further analysis, the Gorda earthquake was judged as not likely to be tsunamigenic (the earthquake magnitude was refined to measure M7.2 and was located in the middle of the Gorda Plate, not on the Cascadia subduction zone (CSZ) boundary between the Gorda Plate and the North American Plate). Additional data confirmed that there were no reports of wave inundation along the coast, and the WC/ATWC reported a widespread tsunami unlikely. However, it did not rule out the possibility for a regional tsunami or landslide-
triggered tsunami. Within an hour of the earthquake, the WC/ATWC canceled the warning for the coast areas of British Columbia, Oregon, Washington, and California.
This tsunami warning came only six months after the horrific tragedies, which took place off the coast of the Indian Ocean during the 2004 tsunami at a time of heightened national fear of tsunami activity. This warning would be the first to be issued for the West Coast for a regional event. Adding to the urgency of decision making action by the TWC was the size and location of the earthquake, the potential for either earthquake- or landslide-generated tsunamis, and the need to issue a statement before potential inundation occurred along the coast (within minutes of the earthquake).
THE EVENT AND RESPONSE IN CALIFORNIA
The June 14, 2005, Gorda Plate earthquake (M7.2) violently shook a wide area of Del Norte and Humboldt Counties, including the cities of Eureka and Crescent City. In assessing the consequent actions at the state and local levels to the tsunami warning it is critical to recognize that the “event” was both a local, widely felt, potentially damaging earthquake, and a potentially damaging near-field tsunami that was the subject of a tsunami warning issued by the WC/ATWC. As noted above, within five minutes of the earthquake, officials at the WC/ATWC issued a tsunami warning to the California State Warning Center (CSWC) both verbally over the National Warning System (NAWAS) and as printed copy over the National Oceanic and Atmospheric Administration/National Weather Service (NOAA/NWS) Weather Wire. These messages were communicated verbally to impacted counties over California’s equivalent to NAWAS, the California Warning System (CALWAS) and by the California Law Enforcement Telecommunications System (CLETS), a teletype service connecting local law enforcement agencies to the California Department of Justice. At the same time that official notification to the CSWC and local governments was occurring, the WC/ATWC notification was being automatically transmitted over the Weather Wire to subscribers of email and pager notification services, over the Emergency Managers Weather Information Notification (EMWIN) service, over the California Emergency Digital Information Service (EDIS) to radio and television newsrooms, and over the California Integrated Seismic Network (CISN) Display to local emergency operations centers.
The WC/ATWC warning was transmitted over the California Law Enforcement Telecommunications System to 22 coastal counties (15 counties directly on the coast and 7 counties that would be impacted by flooding in bays and estuaries), California Highway Patrol (CHP), and State Parks and Recreation. Within 10 minutes following the notification over CLETS, CALWAS was used to issue an initial warning to local emergency responders in the surrounding coastal area. Unfortunately at the time in which this took place, the CSWC was not sufficiently staffed, leaving only two employees to handle the surge of emergency calls. The local recipient of the CSWC notifications is the designated Public Safety Access Point (PSAP), usually the county 911 office and/or fire, law, and emergency medical dispatch, and for the CLETS teletype messages, local law enforcement agencies.
CSWC and Office of Emergency Services procedures provide for secondary notification and
verification of receipt of warning notifications by local emergency managers. Within minutes of the initial notification of the CSWC by the WC/ATWC, Office of Emergency Services (OES) staff were paged and instructed to verify that the notification was received by the local government emergency managers. This verification process was not able to be completed in the northern most counties (those directly impacted by the earthquake and with the greatest potential for being affected by a tsunami) where telephone service was limited by excessive local use after the earthquake and where hundreds of residents had called 911 dispatch centers to report the earthquake. In Crescent City, Del Norte County, a single 911 dispatcher was overwhelmed by the call volume and was not able to receive calls from state personnel verifying receipt of the tsunami warning.
Given the short time span in Humboldt and Del Norte counties between earthquake shaking, issuance of the tsunami warning by the WC/ATWC, and possible tsunami wave arrival, this demand made it difficult for the CSWC and OES to expedite the warning process, a problem that was exacerbated by overloaded wire and cell telephone systems, inadequate staffing at the state and local government emergency operations centers, and limited training at the local government level.
Despite the confusion that was prompted by the conflicting message sent by the Pacific Tsunami Warning and Mitigation System (PTWS), the CSWC transmitted only the first TWC (from the WC/ATWC) warning using CALWAS. The NWS, following NOAA procedure, activated the Emergency Alert System (EAS) and broadcast the tsunami warning to the potentially impacted counties.
Six minutes following the transmission of the tsunami warning, the CSWC held a conference call between the OES Costal Regional Administrator and earthquake/tsunami specialists to remediate the confusion with personnel from counties that might be impacted. As noted above, overload of the local telephone system precluded OES staff from making contact with local officials in Humboldt and Del Norte counties. The state’s satellite telephone system (OASIS) linking OES regional offices and county PSAPs could not be immediately utilized because it could not be accessed from staff residences (the event occurred when OES region staff were at home, as were most local government officials).
Another element of the states’ communication procedures with local governments is the convening of conference calls between local government emergency managers, state officials, and appropriate hazard experts at the time of the issuance of alerts to local government. The state maintains multiple 30-port conference bridge lines for this purpose. Attempts to use the conference call procedures at the time of the tsunami warning were unsuccessful because inbound lines with the scientists at the WC/ATWC were overloaded and local government officials could not be contacted.
As noted above, the population of the impacted areas in northern California was “notified” by the earthquake, by broadcasts over the NOAA All Hazards Radio system, and by stations participating in the EAS. In Crescent City, the tsunami sirens were not sounded until 8:30 PDT (0330 UTC) because of the telephone saturation of the 911 dispatch center and the inability of the single staff person on duty to handle conflicting workload priorities. Spontaneous evacuations took place in several communities. In many of the northern California communities,
where radio and cable television are not locally controlled, the EAS notification was not picked up and broadcast.
At approximately 9:11 PM PDT, the CSWC received a second message from the WC/ATWC, cancelling the tsunami warning after confirmation that a tsunami had not been generated by the earthquake. The CWSC transmitted the notification of the cancellation via CALWAS to the surrounding communities (noncoastal counties), and the CLETS network notified local government agencies in the potential tsunami zone.
THE EVENT AND RESPONSE IN WASHINGTON STATE
Just as California was affected by the tsunami warning on June 14, the state of Washington was also under alert because the WC/ATWC notified it of its assessment for the generation of possible tsunami waves at approximately 7:55 PM PDT. Upon the arrival of this warning, the Washington State EAS, with input from websites and buoy data, decided to inform local officials of the warning of tsunami activity. Unlike the case in California, officials in Washington found the NOAA message transmitted through the WC/ATWC to be clear and had no problems deciphering the message. Minutes later, the news media picked up the message from the PTWC, seemingly contradicting the initial tsunami warning. This conflicting message in addition to the unofficial sources commenting on the progression of the events to the public caused much confusion among the people of Washington. Upon the next hour, Emergency Operation Center (EOC) officials in Washington contacted local law enforcement divisions and other emergency contacts, while the NWS transmitted the primary tsunami warning via EAS to the counties under alert. The warning was also broadcast on television and AM/FM radio stations in the surrounding area. In the state of Washington, under “Home Rule,” local officials are responsible for evacuation orders. Several counties did choose to enact evacuation orders for their communities through local EAS systems. At 8:40, an official State EMD Public Information Officer spoke to several radio and television stations regarding the evacuation suggestions, reminding citizens and officials that the warning of evacuation was only set in place for those living “on the beach” or in “low lying areas.” Approximately 20 minutes later, the State EOC received the tsunami cancellation message, which it transmitted to the public via NAWAS 5 minutes later.
Fortunately, no major tsunami occurred and the events of June 14 served as a “stress test” for the notification system technology, the training of warning personnel, and the response of the public to a potential tsunami. The following were important lessons learned:
The format and content of the information and warning statement from the two TWCs with shared responsibilities for coast lines in the Atlantic and Pacific basin can cause confusion. Tijuana in Baja California was not at risk, but San Diego and Coronado, a few miles to the north in California, were at risk.
Managing information flow from multiple sources (e.g., media, warning centers, NAWAS, etc.) and reducing confusion requires trained and dedicated staff and the
ability to respond to the surge in demand by a sudden onset event like an earthquake and tsunami warning. Ongoing training of officials, the media, and the public is essential, accompanied by documented procedures, checklists, and predetermined priorities for actions.
An earthquake will severely disrupt telecommunications and challenge even redundant systems to perform their dissemination responsibilities.