The volcanic edifice of the Hawaiian islands and seamounts, as well as the surrounding area of shallow sea floor known as the Hawaiian swell, are believed to result from the passage of the oceanic lithosphere over a mantle hotspot. Although geochemical and gravity observations indicate the existence of a mantle thermal plume beneath Hawaii, no direct seismic evidence for such a plume in the upper mantle has yet been found. Here we present an analysis of compressional-to-shear (P-to-S) converted seismic phases, recorded on seismograph stations on the Hawaiian islands, that indicate a zone of very low shear-wave velocity (< 4 km s(-1)) starting at 130-140 km depth beneath the central part of the island of Hawaii and extending deeper into the upper mantle. We also find that the upper-mantle transition zone (410-660 km depth) appears to be thinned by up to 40-50 km to the south-southwest of the island of Hawaii. We interpret these observations as localized effects of the Hawaiian plume conduit in the asthenosphere and mantle transition zone with excess temperature of approximately 300 degrees C. Large variations in the transition-zone thickness suggest a lower-mantle origin of the Hawaiian plume similar to the Iceland plume, but our results indicate a 100 degrees C higher temperature for the Hawaiian plume.

Flank instability and sector collapses, which pose major threats, are common on volcanic islands. On 22 Dec 2018, a sector collapse event occurred at Anak Krakatau volcano in the Sunda Strait, triggering a deadly tsunami. Here we use multiparametric ground-based and space-borne data to show that prior to its collapse, the volcano exhibited an elevated state of activity, including precursory thermal anomalies, an increase in the island’s surface area, and a gradual seaward motion of its southwestern flank on a dipping décollement. Two minutes after a small earthquake, seismic signals characterize the collapse of the volcano’s flank at 13:55 UTC. This sector collapse decapitated the cone-shaped edifice and triggered a tsunami that caused 430 fatalities. We discuss the nature of the precursor processes underpinning the collapse that culminated in a complex hazard cascade with important implications for the early detection of potential flank instability at other volcanoes.

[1] Shear wave splitting measurements using teleseismic SKS and SKKS phases recorded by the INDEPTH-IV arrays has revealed a strong upper mantle anisotropic fabric in northeastern Tibet with large delay times of up to 2.2 s, suggesting that anisotropy exists in both the lithospheric and asthenospheric mantle. The coherence among fast polarization orientations of split core phases and the left-lateral slip on eastern-striking, southern-striking faults in eastern Tibet and the surface deformation fields calculated from both GPS observations and Quaternary fault slip rates support the idea that left-lateral shear strain is the predominant cause of the orientation of the upper mantle petrofabrics. We suggest the bending of the Eastern Himalayan Syntaxis around the foundering Burma-Andaman-Sumatra slab also contributes to the observed seismic anisotropy in the Eastern Himalayan Syntaxis region. Two plausible competing processes are proposed for the flow of asthenosphere in eastern Tibet. In the first, the deforming lithosphere glides over the passive asthenosphere inducing flow in the asthenospheric mantle. In the second, the asthenosphere beneath northeastern Tibet is squeezed between the advancing Indian continental lithosphere and the thick Tarim and Qaidam lithospheric blocks to the north. A westward retreat of the Burma slab from Eurasia may induce flow that is toroidal and located exclusively around the northern edge of the slab. The rotation of fast orientations for stations in the Eastern Himalayan Syntaxis region are consistent with the toroidal flow pattern as well as the rotational deformation of the overlying lithosphere.

The ocean is key to understanding societal threats including climate change, sea level rise, ocean warming, tsunamis, and earthquakes. Because the ocean is difficult and costly to monitor, we lack fundamental data needed to adequately model, understand, and address these threats. One solution is to integrate sensors into future undersea telecommunications cables. This is the mission of the SMART subsea cables initiative (Science Monitoring And Reliable Telecommunications). SMART sensors would "piggyback" on the power and communications infrastructure of a million kilometers of undersea fiber optic cable and thousands of repeaters, creating the potential for seafloor-based global ocean observing at a modest incremental cost. Initial sensors would measure temperature, pressure, and seismic acceleration. The resulting data would address two critical scientific and societal issues: the longterm need for sustained climate-quality data from the under-sampled ocean (e.g., deep ocean temperature, sea level, and circulation), and the near-term need for improvements to global tsunami warning networks. A Joint Task Force (JTF) led by three UN agencies (ITU/WMO/UNESCO-IOC) is working to bring this initiative to fruition. This paper explores the ocean science and early warning improvements available