Juan de Fuca plate seismicity at the northern end of the Cascadia subduction zone

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dc.contributor.authorBolton, Maiclaire Katherineen_US
dc.date.accessioned2024-08-13T00:05:36Z
dc.date.available2024-08-13T00:05:36Z
dc.date.copyright2003en_US
dc.date.issued2003
dc.degree.departmentSchool of Earth and Ocean Sciencesen_US
dc.degree.levelMaster of Science M.Sc.en
dc.description.abstractThe stress regime exhibited by Juan de Fuca plate seismicity, at the northern end of the Cascadia subduction zone, is somewhat enigmatic. These earthquakes are distributed in two concentrations: one beneath the west coast of Vancouver Island (25 to 40 km deep), the second beneath Georgia Strait and Puget Sound (45 to 80 km deep) . Thorough analysis of the Juan de Fuca plate earthquakes was carried out to ascertain patterns within their distribution and clarify the stresses in the study region . No systematic changes in location or dominant patterns in the distribution of the seismicity were observed with relative relocation of these events. Recurrence rates were calculated and b-values for the west coast of Vancouver Island were slightly higher than those for the Georgia Strait/Puget Sound concentration. The smaller recurrence rate reflects the increased proportion of large magnitude events. Seismic moment release calculated for the Juan de Fuca plate earthquakes revealed a slightly greater total moment release for the earthquakes in the west coast of Vancouver Island concentration compared to the Georgia Strait/Puget Sound concentration. No obvious temporal or spatial correlations were observed between these earthquakes and silent slip events based on analysis of cumulative seismic moment release and cumulative event counts of these earthquakes. Focal mechanisms for Juan de Fuca plate earthquakes in the west coast of Vancouver Island and the small (M<4) earthquakes in the Georgia Strait/Puget Sound concentration show a combination of normal and strike-slip faulting, indicating a complex fault pattern. The largest (M>5) events in the Georgia Strait/Puget Sound concentration, current and historic, display dominant normal faulting with down-dip tension . Stress tensor inversion quantified the stresses in the study region, resolving a dominant pattern of north-south compression and east-west tension for the west coast of Vancouver Island concentration. A dominant pattern of near-vertical compression and down-dip tension, indicating normal faulting, was resolved for the Georgia Strait/Puget Sound concentration. The latter agrees with qualitative stress analysis of the largest earthquakes in this concentration.
dc.format.extent238 pages
dc.identifier.urihttps://hdl.handle.net/1828/17051
dc.rightsAvailable to the World Wide Weben_US
dc.titleJuan de Fuca plate seismicity at the northern end of the Cascadia subduction zoneen_US
dc.typeThesisen_US

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