The April 11, 2012, magnitude 8.6 earthquake off the northern coast of Sumatra generated a tsunami that was recorded at sea‐level stations as far as 4800 km from the epicenter and at four ocean bottom pressure sensors (DARTs) in the Indian Ocean. The governments of India, Indonesia, Sri Lanka, Thailand, and Maldives issued tsunami warnings for their coastlines. The United States' Pacific Tsunami Warning Center (PTWC) issued an Indian Ocean‐wide Tsunami Watch Bulletin in its role as an Interim Service Provider for the region. Using an experimental real‐time tsunami forecast model (RIFT), PTWC produced a series of tsunami forecasts during the event that were based on rapidly derived earthquake parameters, including initial location and Mwp magnitude estimates and the W‐phase centroid moment tensor solutions (W‐phase CMTs) obtained at PTWC and at the U. S. Geological Survey (USGS). We discuss the real‐time forecast methodology and how successive, real‐time tsunami forecasts using the latest W‐phase CMT solutions improved the accuracy of the forecast.

We propose a hybrid inversion analysis (HIA) technique aimed at incorporating earthquakes from different seismogenic sources in one single inversion scheme. The application of this technique provides estimations of the source, path, and site effects at 23 strong-motion stations in El Salvador, Central America. The strong-motion dataset comprises 404 triaxial accelerograms corresponding to 63 subduction and upper-crustal earthquakes with M S magnitudes between 3.0 and 7.8. Application of the HIA technique reveals: (1) good matching of the estimated source spectra with those derived from the x 2 point source model; (2) rapid and low attenuation patterns characterizing the upper-crustal volcanic belt and subduction zone, respectively; and (3) soil transfer functions characterized by amplification ratios larger than those derived from spectral ratio techniques by a factor of two. Referencesite-dependent techniques yield similar soil transfer functions at all stations, whereas the horizontal-to-vertical spectral ratio technique yields similar results at sites characterized by clearly predominant peaks.

Abstract. In September 2017, hurricanes Irma and Maria wreaked havoc across the Caribbean region. While obliterating the infrastructure in the Caribbean nations found along their path, both hurricanes gradually destroyed the existing seismic networks. We quantified the impact of the hurricanes on the Pacific Tsunami Warning Center (PTWC) initial tsunami warning capability for the Caribbean region relying on the computation of theoretical earthquake detection and response times after accounting for hurricane-related station outages. The results show that the hurricanes rendered 38 % of the 146 stations available in the Caribbean inoperative. Within the eastern Caribbean region monitored by PTWC the hurricanes exacerbated outages to an astonishing 82 % of the available 76 seismic stations. Puerto Rico, the Virgin Islands, and the Lesser Antilles suffered the brunt of both hurricanes, and their seismic networks nearly disappeared. The double punch delivered by two successive category 5 hurricanes added up to 02:43 and 04:33 min to the earthquake detection and response times, effectively knocking out PTWC's local tsunami warning capabilities in the region. Emergency adjustments, including the temporary reduction of the number of stations required for earthquake detection and ML magnitude release, enabled a faster response to earthquakes in the region than otherwise possible in the aftermath of hurricanes Irma and Maria.

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