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1. Remote Triggering of Icequakes at Mt. Erebus, Antarctica by Large Teleseismic Earthquakes

   https://doi.org/10.1785/0220210027  

   Li, Chenyu; Peng, Zhigang; Chaput, Julien A.; Walter, Jacob I.; Aster, Richard C. (May 2021, Seismological Research Letters)

   null (Ed.)

   Abstract Recent studies have shown that the Antarctic cryosphere is sensitive to external disturbances such as tidal stresses or dynamic stresses from remote large earthquakes. In this study, we systematically examine evidence of remotely triggered microseismicity around Mount (Mt.) Erebus, an active high elevation stratovolcano located on Ross Island, Antarctica. We detect microearthquakes recorded by multiple stations from the Mt. Erebus Volcano Observatory Seismic Network one day before and after 43 large teleseismic earthquakes, and find that seven large earthquakes (including the 2010 Mw 8.8 Maule, Chile, and 2012 Mw 8.6 Indian Ocean events) triggered local seismicity on the volcano, with most triggered events occurring during the passage of the shorter-period Rayleigh waves. In addition, their waveforms and locations for the triggered events are different when comparing with seismic events arising from the persistent small-scale eruptions, but similar to other detected events before and after the mainshocks. Based on the waveform characteristics and their locations, we infer that these triggered events are likely shallow icequakes triggered by dilatational stress perturbations from teleseismic surface waves. We show that teleseismic earthquakes with higher peak dynamic stress changes are more capable of triggering icequakes at Mt. Erebus. We also find that the icequakes in this study are more likely to be triggered during the austral summer months. Our study motivates the continued monitoring of Mount Erebus with dense seismic instrumentation to better understand interactions between dynamic seismic triggering, crospheric processes, and volcanic activity. 

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2. Dynamic Modeling of Interactions between Shallow Slow-Slip Events and Subduction Earthquakes

   https://doi.org/10.1785/0220220138  

   Meng, Qingjun; Duan, Benchun (October 2022, Seismological Research Letters)

   Abstract Shallow slow-slip events (SSEs) contribute to strain release near the shallow portions of subduction interfaces and may contribute to promoting shallow subduction earthquakes. Recent efforts in offshore monitoring of shallow SSEs have provided evidence of possible interactions between shallow SSEs and megathrust earthquakes. In this study, we use a dynamic earthquake simulator that captures both quasi-static (for SSEs) and dynamic (for megathrust earthquakes) slip to explore their interactions and implications for seismic and tsunami hazards. We model slip behaviors of a shallow-dipping subduction interface on which two locally locked patches (asperities) with different strengths are embedded within a conditionally stable zone. We find that both SSEs and earthquakes can occur, and they interact over multiple earthquake cycles in the model. Dynamic ruptures can nucleate on the asperities and propagate into the surrounding conditionally stable zone at slow speeds, generating tsunami earthquakes. A clear correlation emerges between the size of an earthquake and SSE activities preceding it. Small earthquakes rupture only the low-strength asperity, whereas large earthquakes rupture both. Before a large earthquake, periodic SSEs occur around the high-strength asperity, gradually loading stress into its interior. The critically stressed high-strength asperity can be ruptured together with the low-strength one in the large earthquake, followed by a relatively quiet interseismic period with very few SSEs and then a small earthquake. An SSE may or may not directly lead to nucleation of an earthquake, depending on whether a nearby asperity is ready for spontaneously dynamic failure. In addition, because of different SSE activities, the coupling degree may change dramatically between different interseismic periods, suggesting that its estimate based on a short period of observation may be biased. 

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3. Very Low Frequency Earthquakes in Between the Seismogenic and Tremor Zones in Cascadia?

   https://doi.org/10.1029/2021AV000607  

   Fan, Wenyuan; Barbour, Andrew_J; McGuire, Jeffrey_J; Huang, Yihe; Lin, Guoqing; Cochran, Elizabeth_S; Okuwaki, Ryo (March 2022, AGU Advances)

   Abstract Megathrust earthquakes and their associated tsunamis cause some of the worst natural disasters. In addition to earthquakes, a wide range of slip behaviors are present at subduction zones, including slow earthquakes that span multiple orders of spatial and temporal scales. Understanding these events may shed light on the stress or strength conditions of the megathrust fault. Out of all types of slow earthquakes, very low frequency earthquakes (VLFEs) are most enigmatic because they are difficult to detect reliably, and the physical nature of VLFEs are poorly understood. Here we show three VLFEs in Cascadia that were dynamically triggered by a 2009 Mw 6.9 Canal de Ballenas earthquake in the Gulf of California. The VLFEs likely locate in between the seismogenic zone and the Cascadia episodic tremor and slip (ETS) zone, including one event with a moment magnitude of 5.7. This is the largest VLFE reported to date, causing clear geodetic signals. Our results show that the Cascadia megathrust fault might slip rapidly at some spots in this gap zone, and such a permissible slip behavior has direct seismic hazard implications for coastal communities and perhaps further inland. Further, the observed seismic sources may represent a new class of slip events, whose characteristics do not fit current understandings of slow or regular earthquakes. 

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4. Triggering Intensity Changes Over Time and Space as Measured by Continuous Waveforms in Southern California

   https://doi.org/10.1029/2024JB030004  

   Guo, Huiyun; Brodsky, Emily_E; Miyazawa, Masatoshi (June 2025, Journal of Geophysical Research: Solid Earth)

   Abstract Dynamic triggering of earthquakes is when seismic waves from earthquakes induce seismic activity at a distance. The observability of the seismic wave stresses and their results presents a unique opportunity to understand earthquake interactions and associated hazard implications. The extent and timing of dynamic triggering at given specific stress changes still remain inadequately predicted due to limited studies and data sets. In particular, the requirement for complete, well‐characterized catalogs to detect triggering systematically seriously limits the types of studies possible. To address this, we utilized 7‐year continuous waveform data from 239 stations in southern California and used PhaseNet for phase picking to identify local earthquakes and measure triggering without constructing any earthquake catalog. We map the triggering intensity over the region and find that overall, the Mojave segment of the San Andreas is the most easily triggered region. However, the spatial pattern changes after the Ridgecrest earthquake and the area appears to become much less prone to triggering, likely due to an exhaustion of the faults near failure in the immediate aftermath of the Ridgecrest sequence. We further observe a slow decay rate of dynamic triggering and conclude that low‐frequency waves (0.04–0.1 Hz) may be more effective in dynamic triggering than high‐frequency waves (1–3 Hz) which is consistent with a rate‐state assisted aseismic creep or hydrological triggering mechanism. 

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5. Updated concepts of seismic gaps and asperities to assess great earthquake hazard along South America

   https://doi.org/10.1073/pnas.2216843119  

   Lay, Thorne; Nishenko, Stuart P. (December 2022, Proceedings of the National Academy of Sciences)

   So far in this century, six very large–magnitude earthquakes ( M W ≥ 7.8) have ruptured separate portions of the subduction zone plate boundary of western South America along Ecuador, Peru, and Chile. Each source region had last experienced a very large earthquake from 74 to 261 y earlier. This history led to their designation in advance as seismic gaps with potential to host future large earthquakes. Deployments of geodetic and seismic monitoring instruments in several of the seismic gaps enhanced resolution of the subsequent faulting processes, revealing preevent patterns of geodetic slip deficit accumulation and heterogeneous coseismic slip on the megathrust fault. Localized regions of large slip, or asperities, appear to have influenced variability in how each source region ruptured relative to prior events, as repeated ruptures have had similar, but not identical slip distributions. We consider updated perspectives of seismic gaps, asperities, and geodetic locking to assess current very large earthquake hazard along the South American subduction zone, noting regions of particular concern in northern Ecuador and Colombia (1958/1906 rupture zone), southeastern Peru (southeasternmost 1868 rupture zone), north Chile (1877 rupture zone), and north-central Chile (1922 rupture zone) that have large geodetic slip deficit measurements and long intervals (from 64 to 154 y) since prior large events have struck those regions. Expanded geophysical measurements onshore and offshore in these seismic gaps may provide critical information about the strain cycle and fault stress buildup late in the seismic cycle in advance of the future great earthquakes that will eventually strike each region. 

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