Triggering an unexpected earthquake in an uncoupled subduction zone

Herman, M. W.; Furlong, Kevin P.

doi:10.1126/sciadv.abf7590

Cited by 42 publications

(29 citation statements)

References 44 publications

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“…The lateral displacement variations can impose large-magnitude, right-lateral shear stresses on the M7.6 rupture plane geometry, assuming the target fault plane was north-south striking and east dipping with a dip angle 50 • . However, we note that the available geodetic observations infer only 30%±10% coupling in the western portion of Semidi segment (Drooff and Freymueller, 2021) which is much lower than the 100% assumed by Herman and Furlong (2021), for the whole Semidi segment. Therefore, interseismic coupling variation between the Semidi and Shumagin segments may contribute to the shear stress accumulation on the M7.6 rupture plane, but geodetic evidence suggests this contribution may be more modest in magnitude.…”

Section: The M76 Slab-tear Earthquake Source Regioncontrasting

confidence: 63%

“…Alternatively, shear stresses could be caused by spatial variations of elastic coupling along the megathrust interface. Herman and Furlong (2021) present models that simulate the effect of laterally variable coupling. The preferred models represent the Semidi segment to be highly coupled while the Shumagin segment has low coupling.…”

Section: The M76 Slab-tear Earthquake Source Regionmentioning

confidence: 99%

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Subduction earthquakes controlled by incoming plate geometry: The 2020 M>7.5 Shumagin, Alaska, earthquake doublet

Jiang¹,

González²,

Bürgmann³

2022

Preprint

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In 2020, an earthquake doublet, a M7.8 on July 22nd and a M7.6 on October 19th, struck the Alaska-Aleutian subduction zone beneath the Shumagin Islands. This is the first documented earthquake doublet, of considerable size, involving a megathrust event and a strike-slip event, with both events producing deeply buried ruptures. The first event partially ruptured a seismic gap, which has not hosted large earthquakes since 1917, and the second event was unusual as it broke a trench-perpendicular fault within the incoming oceanic slab. We used an improved Bayesian geodetic inversion method to estimate the fault slip distributions of the major earthquakes using Interferometric Synthetic Aperture Radar (InSAR) wrapped phase and Global Navigation Satellite Systems (GNSS) offsets data. The geodetic inversions reveal that the Shumagin seismic gap is multi-segmented, and the M7.8 earthquake ruptured the eastern segment from 14 km down to 44 km depth. The coseismic slip occurred along a more steeply, 26-degree dipping segment, and was bounded up-dip by a bend of the megathrust interface to a shallower 8-degree dip angle connecting to the trench. The model for the M7.6 event tightly constrained the rupture depth extent to 23-37 km, within the depth range of the M7.8 coseismic rupture area. We find that the M7.6 event ruptured the incoming slab across its full seismogenic thickness, potentially reactivating subducted Kula-Resurrection seafloor-spreading ridge structures. Coulomb stress transfer models suggest that coseismic and/or postseismic slip of the M7.8 event could have triggered the M7.6 event. This unusual intraslab event could have been caused by accumulation and localization of flexural elastic shear stresses at the slab bending region. We conclude that the segmented megathrust structure and the location of intraslab fault structures limited the rupture dimensions of the M7.8 event and are responsible for the segmentation of the Shumagin seismic gap. Our study suggests that the western and shallower up-dip segments of the seismic gap did not fail and remain potential seismic and tsunami hazard sources. The unusual earthquake doublet provides a unique opportunity to improve our understanding of the role of the subducting lithosphere structure in the segmentation of subduction zones.

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Section: The M76 Slab-tear Earthquake Source Regioncontrasting

confidence: 63%

Section: The M76 Slab-tear Earthquake Source Regionmentioning

confidence: 99%

Subduction earthquakes controlled by incoming plate geometry: The 2020 M>7.5 Shumagin, Alaska, earthquake doublet

Jiang¹,

González²,

Bürgmann³

2022

Preprint

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“…The event sequence started on 22 July 2020, when the M7. 8 Simeonof megathrust earthquake at least partly filled (3)(4)(5)(6) the Shumagin seismic gap (Fig. 1).…”

Section: Introductionmentioning

confidence: 93%

“…This enigmatic segment of the plate boundary last partially ruptured in an M 7.4 earthquake in 1917 ( 7 ). An M 7.6 strike-slip event within the downgoing plate struck in October 2020 to the west of the Simeonof event ( 8 ). The Simeonof event was followed by the 29 July 2021, M 8.2 Chignik megathrust earthquake, the largest event in the United States since the 1965 M 8.7 Rat Islands earthquake.…”

Section: Introductionmentioning

confidence: 99%

Cascading rupture of a megathrust

et al. 2022

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Understanding variability in the size and location of large earthquakes along subduction margins is crucial for evaluating seismic and tsunami hazards. We present a coseismic slip model for the 2021 M 8.2 Chignik earthquake and investigate the relationship of this earthquake to previous major events in the Alaska Peninsula region and to interseismic coupling. Stress changes from the 2020 M 7.8 Simeonof event triggered the Chignik event, and together, the earthquakes partially filled an unruptured section along a 3000-km subduction margin that has experienced a series of ruptures along almost its entire length over the past century. Variations in coupling and structural characteristics may make the region more prone to nucleating M 7 to M 8 events rather than larger M > 8.5 earthquakes. Stress changes and rupture areas suggest that the two recent earthquakes may be part of an 80-year-long rupture cascade and may have advanced seismic hazard in the region.

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“…In addition, the tsunami excitation can be further exacerbated by displacement along splay faults and earthquake-triggered submarine landslides (e.g., Carter et al, 2014), which are very difficult to detect by seismology alone. A recent example is the strike-slip Alaska earthquake of October 19, 2020 (Herman and Furlong, 2021). The tsunami recorded on nearby DART buoys was much greater than expected given the Pacific Tsunami Warning Center's (PTWC's) forecast based on the CMT.…”

Section: Seismic and Tsunami Monitoring And Warningmentioning

confidence: 99%

SMART Subsea Cables for Observing the Earth and Ocean, Mitigating Environmental Hazards, and Supporting the Blue Economy

et al. 2022

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The Joint Task Force, Science Monitoring And Reliable Telecommunications (JTF SMART) Subsea Cables, is working to integrate environmental sensors for ocean bottom temperature, pressure, and seismic acceleration into submarine telecommunications cables. The purpose of SMART Cables is to support climate and ocean observation, sea level monitoring, observations of Earth structure, and tsunami and earthquake early warning and disaster risk reduction, including hazard quantification. Recent advances include regional SMART pilot systems that are the first steps to trans-ocean and global implementation. Examples of pilots include: InSEA wet demonstration project off Sicily at the European Multidisciplinary Seafloor and water column Observatory Western Ionian Facility; New Caledonia and Vanuatu; French Polynesia Natitua South system connecting Tahiti to Tubaui to the south; Indonesia starting with short pilot systems working toward systems for the Sumatra-Java megathrust zone; and the CAM-2 ring system connecting Lisbon, Azores, and Madeira. This paper describes observing system simulations for these and other regions. Funding reflects a blend of government, development bank, philanthropic foundation, and commercial contributions. In addition to notable scientific and societal benefits, the telecommunications enterprise’s mission of global connectivity will benefit directly, as environmental awareness improves both the integrity of individual cable systems as well as the resilience of the overall global communications network. SMART cables support the outcomes of a predicted, safe, and transparent ocean as envisioned by the UN Decade of Ocean Science for Sustainable Development and the Blue Economy. As a continuation of the OceanObs’19 conference and community white paper (Howe et al., 2019, doi: 10.3389/fmars.2019.00424), an overview of the SMART programme and a description of the status of ongoing projects are given.

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Triggering an unexpected earthquake in an uncoupled subduction zone

Cited by 42 publications

References 44 publications

Subduction earthquakes controlled by incoming plate geometry: The 2020 M>7.5 Shumagin, Alaska, earthquake doublet

Subduction earthquakes controlled by incoming plate geometry: The 2020 M>7.5 Shumagin, Alaska, earthquake doublet

Cascading rupture of a megathrust

SMART Subsea Cables for Observing the Earth and Ocean, Mitigating Environmental Hazards, and Supporting the Blue Economy

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