Compilation and Analysis of Two Decades Worth of Tsunami Bulletins Issued By the Pacific Tsunami Warning Center (Ptwc)

Abstract eng:
The PTWC has operated under the Tsunami Program of UNESCO’s Intergovernmental Oceanographic Commission as an international tsunami warning center (TWC) for nations with Pacific coasts for fifty years (1965-present), and similarly as an interim center for the Indian Ocean (2005-2013) and Caribbean Sea (2005-present). It also operates as the US domestic TWC for the State of Hawaii (1949-present) and for American Samoa, Guam, and the Commonwealth of the Northern Mariana Islands (2014-present). As part of its routine operations, the PTWC monitors seismic networks across the globe providing data in near-real time from more than 600 stations. Analysis of data from these stations allows PTWC scientists to detect and locate large earthquakes, assess their magnitude, evaluate their tsunamigenic potential, and send initial tsunami message products when necessary just a few minutes after the earthquake. The PTWC, however, not always had this rapid response. To evaluate PTWC's historical performance we compiled a database of tsunami bulletins issued by the PTWC from 1998 to April 2016. We scanned the available archives for the Federal Aviation Administration (FAA) and the Global Telecommunications System (GTS) communications' circuits to retrieve the first tsunami bulletin issued for 647 earthquakes. We then parsed these bulletins and extracted their parametric data to evaluate PTWC's performance based on essential statistics such as message delay time, epicenter offsets, and magnitude residuals. To this end, we cross-validated bulletins reporting magnitudes between 6.0 and 8.7 with more authoritative source parameters later reported by the National Earthquake Information Center (NEIC), and the Global Centroid Moment Tensor (GCMT) project. Analysis of these data gives an overall historical median value of 10 minutes for the message delay times, 19 km for the epicentral offsets, and 0.2 units for the magnitude residuals. A new magnitude dependent correction formula derived from the analysis of the Mwp magnitudes reported in the PTWC bulletins provides better matching with the GCMT moment magnitudes. In the late 1990s it took the PTWC over an hour to send its first official message product. As of April 2016, however, the PTWC had decreased the median message delay time for teleseismic events to 6 minutes and 44 seconds, while keeping both the epicentral offsets and the magnitude residuals within the same historical margin of error. This 90% reduction of the message latencies helps to effectively warn coasts nearest a tsunamigenic earthquake, where the generated tsunami waves usually have the greatest impact, as well as to give coasts further away more time to prepare for their arrival.

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