Interseismic lithospheric response of the southern end of the Cascadia subduction zone since the 1992 Cape Mendocino m 7.1 earthquake
Graduation Date
2016
Document Type
Thesis
Program
Other
Program
Thesis (M.S.)--Humboldt State University, Geology, 2016
Committee Chair Name
Mark Hemphill-Haley
Committee Chair Affiliation
Cal Poly Humboldt Faculty or Staff
Keywords
GPS, Uplift, Singley Flat, Subduction, Mussel Rock, Earthquakes, Subsidence, Cape Mendocino, Mendocino triple junction, Cascadia subduction zone, Humboldt State University -- Theses -- Geology, Interseismic, Intertidal organism
Abstract
The Cascadia subduction zone (CSZ) in the Pacific Northwest, where the Gorda plate is subducting beneath the North American plate, may be capable of producing M 9 earthquakes. At its southern end, the CSZ terminates at the Mendocino triple junction in northern California, a region of frequent seismic activity. Unique among this seismicity was the 1992 M 7.1 Cape Mendocino earthquake, which caused up to 1.4 m of measured coseismic uplift and may have been a segmented rupture of the southern end of the CSZ. The coseismic deformation was measured using Vertical Extent of Mortality of intertidal organisms, as well as a first order NGS leveling survey. Using static GPS relocation of leveling benchmarks and the position of intertidal organisms I measured vertical crustal deformation over the 23 years since the 1992 event. If this earthquake had occurred on the megathrust interface between the Gorda and North American plates, I expected to see 10 – 20 cm of subsidence near the peak of coseismic uplift. However, this earthquake could have occurred along a subsidiary fault within the accretionary wedge or upper plate, in which case the deformation rate should be much lower. Benchmark relocation and intertidal organism relocation yield maximum vertical deformation of 1 mm/yr. These low interseismic deformation rates measurements indicate that the 1992 M 7.1 Cape Mendocino earthquake was not rupture of the subduction zone interface, but likely occurred within the upper plate accretionary complex on a subsidiary fault.
Recommended Citation
Vermeer, Jessica, "Interseismic lithospheric response of the southern end of the Cascadia subduction zone since the 1992 Cape Mendocino m 7.1 earthquake" (2016). Cal Poly Humboldt theses and projects. 1451.
https://digitalcommons.humboldt.edu/etd/1451
https://scholarworks.calstate.edu/concern/theses/gh93h171m