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  • 1
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    Great (≥Mw8.0) megathrust earthquakes and the subduction of excess sediment and bathymetrically smooth seafloor (2015)
    Geological Society of America
    In:  Geosphere, 11 (2). pp. 236-265.
    Details
    Publication Date: 2019-08-06
    Description: Using older and in part fl awed data, Ruff (1989) suggested that thick sediment entering the subduction zone (SZ) smooths and strengthens the trench-parallel distribution of interplate coupling. This circumstance was conjectured to favor rupture continuation and the generation of high-magnitude (≥Mw8.0) interplate thrust (IPT) earthquakes. Using larger and more accurate compilations of sediment thickness and instrumental (1899 to January 2013) and pre-instrumental era (1700–1898) IPTs (n = 176 and 12, respectively), we tested if a compelling relation existed between where IPT earthquakes ≥Mw7.5 occurred and where thick (≥1.0 km) versus thin (≤1.0 km) sedimentary sections entered the SZ. Based on the new compilations, a statistically supported statement (see Summary and Conclusions) can be made that high-magnitude earthquakes are most prone to nucleate at well-sedimented SZs. For example, despite the 7500 km shorter global length of thicksediment trenches, they account for ~53% of instrumental era IPTs ≥Mw8.0, ~75% ≥Mw8.5, and 100% ≥Mw9.1. No megathrusts 〉Mw9.0 ruptured at thin-sediment trenches, whereas three occurred at thick-sediment trenches (1960 Chile Mw9.5, 1964 Alaska Mw9.2, and 2004 Sumatra Mw9.2). However, large Mw8.0–9.0 IPTs commonly (n = 23) nucleated at thin-sediment trenches. These earthquakes are associated with the subduction of low-relief ocean floor and where the debris of subduction erosion thickens the plate-separating subduction channel. The combination of low bathymetric relief and subduction erosion is inferred to also produce a smooth trench-parallel distribution of coupling posited to favor the characteristic lengthy rupturing of highmagnitude IPT earthquakes. In these areas subduction of a weak sedimentary sequence further enables rupture continuation
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/GES01079.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Morphotectonics of the Pacific convergent margin of Costa Rica (1995)
    Geological Society of America
    In:  In: Geologic and Tectonic Development of the Caribbean Plate Boundary in Southern Central America. Geological Society of America Special Paper, 295 . Geological Society of America, Boulder, Colo., pp. 291-308. ISBN 0-8137-2295-0
    Details
    Publication Date: 2016-01-11
    Description: Offshore of the Pacific side of Costa Rica, the Caribbean plate converges with the subducting Cocos plate along the Middle America Trench. The tectonics of both plates, from the Cocos Ridge to the Nicoya Peninsula, were studied with swathmapping, magnetic anomalies, and samples. Three morphological domains on the Cocos plate were defined by mapping. The broadly arched Cocos Ridge forms the southeastern domain. Adjacent to the northwest flank of Cocos Ridge is a domain where seamounts and their aprons cover about 40% of the ocean floor. Farther northwest, a sharp juncture in the oceanic crust separates the seamount domain from a deep sea plain. These three contrasting oceanic seafloor morphologies are mimicked in the morphology of the Pacific continental margin of Costa Rica. Opposite the subducting Cocos Ridge are a broad continental shelf and Osa Peninsula, which are attributed to large-scale domal uplift. Where the seamount domain has been subducted, a rugged continental slope has developed, including 55-km-long furrows trending parallel to the Cocos-Caribbean interplate convergence direction. We propose that the furrows represent paths of disruption produced by subducting seamounts. Where the smooth deep sea plain has been subducted, a well-organized accretionary prism covered by slope deposits forms a relatively smooth morphology. The Costa Rican margin illustrates the effects of subducting seafloor morphology on the continental margin structure and morphology.
    Type: Book chapter , NonPeerReviewed
    Format: text
    DOI: 10.1130/SPE295-p291
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    OceanRep: Book chapter
  • 3
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    Glacial advance in the Gulf of Alaska Area implied by ice-rafted materia (1976)
    Geological Society of America
    In:  In: Investigation of Late Quaternary paleoceanography and paleoclimatology. , ed. by Cline, R. M. and Hays, J. D. Geological Society of America Memoir, 145 . Geological Society of America, Boulder, Colo., pp. 411-422.
    Details
    Publication Date: 2015-07-23
    Description: An abundance curve for ice-rafted detritus based on data from cores from the Gulf of Alaska depicts the main continental glacial events, on which curves of a series of shorter events are superimposed. Interpretation of the shorter curves is limited by the difficulty of distinguishing between glacial events and the “noise level” of the data. However, the correspondence is remarkable between the curves developed here and curves of Pleistocene ocean water and ice temperatures, glacial advances, and lake levels. The curves suggest cycles of glacial advance lasting 12,000 to 15,000 yr; if more cores were available, the cyclicity would probably be established with greater confidence. Our studies of ice-rafted detritus in the Gulf of Alaska revealed that under certain conditions, a rapidly deposited deep-sea marine section, which characteristically has temporal continuity, can record variations in the intensity of alpine glaciation, which characteristically has high sensitivity to climatic change.
    Type: Book chapter , NonPeerReviewed
    Format: text
    DOI: 10.1130/MEM145-p411
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    OceanRep: Book chapter
  • 4
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    The Shumagin seismic gap structure and associated tsunami hazards, Alaska convergent margin (2019)
    Geological Society of America
    In:  Geosphere, 15 (2). pp. 324-341.
    Details
    Publication Date: 2022-01-31
    Description: The potential for a major earthquake in the Shumagin seismic gap, and the tsunami it could generate, was reported in 1971. However, while potentially tsunamigenic splay faults in the adjacent Unimak and Semidi earthquake segments are known, such features along the Shumagin segment were undocumented until recently. To investigate margin structure and search for splay faults, we reprocessed six legacy seismic records and also processed seismic data acquired by RV Langseth during the ALEUT project (cf. Bécel et al., 2017). All records show splay faults separating the frontal prism from the margin framework. A ridge uplifted by the splay fault hanging wall extends along the entire segment. At the plate interface, the splay fault cuts across subducted sediment strata in some images, whereas in others, the plate interface sediment cuts across the fault. Splay fault zones are commonly associated with subducting lower-plate relief. Along the upper slope, beneath a sediment cover, major normal faults dipping landward and seaward border a ridge of basement rock. The faults displace a regional unconformity that elsewhere received Oligocene–Miocene sediment. Low seafloor scarps above some normal faults indicate recent tectonism. The buried ridge is a continuation of the Unimak Ridge structure that extends NE of the Unimak/Shumagin segment boundary. Some geological characteristics of the Shumagin segment differ from those of other Alaskan earthquake segments, but a causal link to the proposed Shumagin creeping seismic behavior is equivocal.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1130/GES01657.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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