The International Federation of Digital Seismographic Networks (FDSN) is a non-governmental organization formed by institutions dedicated to seismological research and seismic monitoring. The FDSN is a successful complement to the International Seismological Centre (ISC) in pursuing a more than a century old tradition of global seismic data exchange. The main goal of the FDSN is the production and dissemination of seismic waveform data from high fidelity seismic observatories. The federation is formed by 65 organizations from 52 countries that contribute data to three main data centers in the United States, Europe, and Japan. A subset of the stations that conform the FDSN send real-time to the data management center (DMC) of the Incorporated Research Institutions of Seismology (IRIS) in the United States. Data from this real-time network is crucial to the determination of the seismic parameters of large earthquakes in a very short time after their occurrence and to support the efforts of institutions that are responsible for disaster relief or prevention. Most notably, tsunami warning centers use this information as a fundamental underpinning to issue warnings and alerts. The FDSN is an early participant of the global earth observation system of systems (GEOSS), contributing high-quality, timely and freely accessible seismic data. The purpose of this paper is to provide an overview of the FDSN from the viewpoint of an integrated system of observatories and to share with other GEOSS networks the successes, challenges and lessons learned by the FDSN in promoting the open and free access of seismological data for the benefit of scientific research and disaster prevention and mitigation.

The Hawaiian Islands' location in the middle of the Pacific Ocean is threatened by tsunamis from great earthquakes in nearly all directions. Historical great earthquakes M_w > 8.5 in the last 100 years have produced large inundations and loss of life in the islands but cannot account for a substantial (≤ 600 m³) paleotsunami deposit in the Makauwahi sinkhole on the Island of Kaua‘i. Using high‐resolution bathymetry and topography we model tsunami inundation of the sinkhole caused by an earthquake with a moment magnitude of M_w ~9.25 located in the eastern Aleutians. A preponderance of evidence indicates that a giant earthquake in the eastern Aleutian Islands circa 1425–1665 A.D.—located between the source regions of the 1946 and 1957 great tsunamigenic earthquakes—created the paleotsunami deposit in Kaua‘i. A tsunami deposit in the Aleutians dated circa 1530–1660 A.D. is consistent with this eastern Aleutian source region.

The 2011 Tohoku earthquake and tsunami motivated an analysis of the potential for great tsunamis in Hawai‘i that significantly exceed the historical record. The largest potential tsunamis that may impact the state from distant, Mw 9 earthquakes—as forecast by two independent tsunami models—originate in the Eastern Aleutian Islands. This analysis is the basis for creating an extreme tsunami evacuation zone, updating prior zones based only on historical tsunami inundation. We first validate the methodology by corroborating that the largest historical tsunami in 1946 is consistent with the seismologically determined earthquake source and observed historical tsunami amplitudes in Hawai‘i. Using prior source characteristics of Mw 9 earthquakes (fault area, slip, and distribution), we analyze parametrically the range of Aleutian–Alaska earthquake sources that produce the most extreme tsunami events in Hawai‘i. Key findings include: (1) An Mw 8.6 ± 0.1 1946 Aleutian earthquake source fits Hawai‘i tsunami run-up/inundation observations, (2) for the 40 scenarios considered here, maximal tsunami inundations everywhere in the Hawaiian Islands cannot be generated by a single large earthquake, (3) depending on location, the largest inundations may occur for either earthquakes with the largest slip at the trench, or those with broad faulting over an extended area, (4) these extremes are shown to correlate with the frequency content (wavelength) of the tsunami, (5) highly variable slip along the fault strike has only a minor influence on inundation at these tele-tsunami distances, and (6) for a given maximum average fault slip, increasing the fault area does not generally produce greater run-up, as the additional wave energy enhances longer wavelengths, with a modest effect on inundation.

The generation of microseisms is investigated at the ALOHA Cabled Observatory (ACO) north of Oahu during the close passage of Hurricane Lester in September 2016. Sensors include a seafloor ALOHA pressure gauge at ACO, KIP seismic data on Oahu, and nearby wave buoys. Examination of frequency‐direction spectra from wave buoys and numerical wave model outputs confirms two separate microseism generation processes: At frequencies 0.225 Hz, microseisms are dominated by waves originating from Hurricane Lester. The cross‐over frequency (0.225 Hz) occurs where the ocean wave group velocity matches the Hurricane storm track speed. Correcting for impedance, the spectrogram for energy at ALOHA closely correlates with KIP. When opposing swells meet at a distance from the Hurricane Lester and ACO, the resulting microseisms also spread geometrically in propagation to ALOHA and KIP, effectively equivalent to 1/R². At the microseism peak, 4 September, the dominant motions of KIP are observed with retrograde particle motion characteristic of Rayleigh modes, in both the radial‐vertical and transverse‐vertical sagittal planes at distances of ≲400 km from the eye. Otherwise, the energy on the transverse component is comparable to the radial component. We hypothesize that the observed transverse energy arises locally: (1) from the extended microseism source region near ACO and (2) and from scattering by dipping structure and anisotropy embedded in the crust during emplacement at the Pacific‐Farallon ridge.

I review the unusual swarm of 50 earthquakes, $Mw$ 5.2–5.4, which occurred at Kīlauea caldera between May and August 2018. Given the strong similarity in published source mechanisms derived by centroid moment tensor (CMT) methods, I stacked the P waves from a global distribution of stations from local to antipodal distances. The composite source mechanism is consistent with a normal planar fault striking 335° NNW, dipping 78° W, with a rake nearly $−90°$⁠. The differences between the composite source and waveform‐derived sources are due in part to the choice of source depth, seismic velocity, and rigidity beneath Kīlauea summit. Antipodal PKIKP observations of the bottom of the source are derived from stacked data from three Global Seismographic Network (GSN) stations at $∼175°Δ$ in southern Africa. The stacked PKIKP displacement data show dilatational first motions, apparently inconsistent with proposed piston models of the volcano–earthquake activity for comparable swarms observed in the Galapagos, Miyakejima, and Iceland. As recognized in these prior studies, the vertical‐P compensated linear vector dipole (CLVD) moment tensor solutions likely result from arcuate faults, which collectively circumscribe the caldera. The interevent times of the swarm sequence are not random; rather, the time interval between events increases by $∼1/2hr$ for each earthquake.