Compilation and Analysis of a Database of Local Tsunami Bulletins issued by the Pacific Tsunami Warning Center (PTWC) to the Hawaii Emergency Management Agency (HI-EMA) between September 2003 and July, 2015

Abstract:

The PTWC functions not only as official international tsunami warning center (TWC) for nations with coasts around the Pacific rim, the Caribbean, and other regions of the world, but also as the local TWC for the State of Hawaii. The PTWC began sending local tsunami messages to HI-EMA only since September, 2003. As part of its routine operations, the PTWC strives to send a local tsunami message product for any Hawaii earthquake with a 4.0 magnitude or larger within five minutes of origin time. To evaluate PTWC's performance in that regard, however, we must first compile a suitable local tsunami bulletins' database. For this purpose, we scanned all the available logs for the Federal Aviation Administration (FAA) communications' circuit between 2003 and 2015 and retrieved 104 local bulletins. We parsed these bulletins and extracted the parametric data needed to evaluate PTWC's performance in terms of essential statistics such as message delay time, epicenter offsets, and magnitude residuals as compared with more authoritative earthquake source parametrizations. To that end, we cross-validated 88 of these seismic events having magnitudes between 2.8 and 6.7 with the corresponding source parameters obtained from the USGS Hawaiian Volcano Observatory (HVO) and the National Earthquake Information Center's (NEIC) online catalog. Analysis of events with magnitude 4.0 or larger gives a median message delay time of 3 minutes and 33 seconds, a median epicentral offset of 3.2 km, and a median magnitude residual of 0.2 unit. Several message delay outliers exist due to the fact that PTWC has sent local tsunami information statements (TIS) for felt events with magnitudes as small as 2.8 located west of the Big Island. Routine use of a synthetic Wood-Anderson magnitude since the end of 2012 appears to have brought consistency to PTWC's local magnitude estimates and a reduction in the message delays. Station site corrections, a refined attenuation model, and optimization of the peak-amplitude search window may improve magnitude estimates. Improved dissemination software, regional moment tensor determinations for rapid magnitude estimation in addition to ML and Mwp can result in yet faster and more accurate tsunami message products.