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Abstract Most great earthquakes on subduction zone plate boundaries have large coseismic slip concentrated along the contact between the subducting slab and the upper plate crust. On 4 March 2021, a magnitude 7.4 foreshock struck 1 hr 47 min before a magnitude 8.1 earthquake along the northern Kermadec island arc. The mainshock is the largest well‐documented underthrusting event along the ∼2,500‐km long Tonga‐Kermadec subduction zone. Using teleseismic, geodetic, and tsunami data, we find that all substantial coseismic slip in the mainshock is located along the mantle/slab interface at depths from 20 to 55 km, with the large foreshock nucleating near the down‐dip edge. Smaller foreshocks and most aftershocks are located up‐dip of the mainshock, where substantial prior moderate thrust earthquake activity had occurred. The upper plate crust is ∼17 km thick in northern Kermadec with only moderate‐size events along the crust/slab interface. A 1976 sequence withM_Wvalues of 7.9, 7.8, 7.3, 7.0, and 7.0 that spanned the 2021 rupture zone also involved deep megathrust rupture along the mantle/slab contact, but distinct waveforms exclude repeating ruptures. Variable waveforms for eight deep M6.9+ thrusting earthquakes since 1990 suggest discrete slip patches distributed throughout the region. The ∼300‐km long plate boundary in northern Kermadec is the only documented subduction zone region where the largest modeled interplate earthquakes have ruptured along the mantle/slab interface, suggesting that local frictional properties of the putatively hydrated mantle wedge may involve a dense distribution of Antigorite‐rich patches with high slip rate velocity weakening behavior in this locale. 

Abstract On 18 November 2022, a large earthquake struck offshore southern Sumatra, generating a tsunami with 25 cm peak amplitude recorded at tide gauge station SBLT. OurW‐phase solution indicates a shallow dip of 6.2°, compatible with long‐period surface wave radiation patterns. Inversion of teleseismic body waves indicates a shallow slip distribution extending from about 10 km deep to near the trench with maximum slip of ∼4.1 m and seismic moment of  Nm (M_W7.3). Joint modeling of seismic and tsunami data indicates a shallow rigidity of ∼23 GPa. We find a low moment‐scaled radiated energy of , similar to that of the 2010M_W7.8 Mentawai event () and other tsunami earthquakes. These characteristics indicate that the 2022 event should be designated as a smaller moment magnitude tsunami earthquake compared to the other 12 well‐documented global occurrences since 1896. The 2022 event ruptured up‐dip of the 2007M_W8.4 Bengkulu earthquake, demonstrating shallow seismogenic capability of a megathrust that had experienced both a deeper seismic event and adjacent shallow aseismic afterslip. We consider seismogenic behavior of shallow megathrusts and concern for future tsunami earthquakes in subduction zones globally, noting a correlation between tsunami earthquake occurrence and subducting seafloor covered with siliceous pelagic sediments. We suggest that the combination of pelagic clay and siliceous sediments and rough seafloor topography near the trench play important roles in controlling the genesis of tsunami earthquakes along Sumatra and other regions, rather than the subduction tectonic framework of accretionary or erosive margin. 

The 2022 Tonga eruption produced ground motions dominated by force interactions between the solid Earth and atmosphere. 

Abstract In the aftermath of a significant earthquake, seismologists are frequently asked questions by the media and public regarding possible interactions with recent prior events, including events at great distances away, along with prospects of larger events yet to come, both locally and remotely. For regions with substantial earthquake catalogs that provide information on the regional Gutenberg–Richter magnitude–frequency relationship, Omori temporal aftershock statistical behavior, and aftershock productivity parameters, probabilistic responses can be provided for likelihood of nearby future events of larger magnitude, as well as expected behavior of the overall aftershock sequence. However, such procedures generally involve uncertain extrapolations of parameterized equations to infrequent large events and do not provide answers to inquiries about long-range interactions, either retrospectively for interaction with prior remote large events or prospectively for interaction with future remote large events. Dynamic triggering that may be involved in such long-range interactions occurs, often with significant temporal delay, but is not well understood, making it difficult to respond to related inquiries. One approach to addressing such inquiries is to provide retrospective or prospective occurrence histories for large earthquakes based on global catalogs; while not providing quantitative understanding of any physical interaction, experience-based guidance on the (typically very low) chances of causal interactions can inform public understanding of likelihood of specific scenarios they are commonly very interested in.