Graduate Thesis Or Dissertation

Source Parametrization of Earthquakes along Juan de Fuca Transform Boundaries

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  • The Juan de Fuca plate system is what remains of Farallon plate subducting under the continental North American plate. Blanco Transform Fault Zone (BTFZ) consists of a network of strike-slip faults discontinued by pull apart depressions which o↵sets the Juan de Fuca Ridge and the Gorda Ridge. Detailed analysis of earthquake source parameters are done using onshore stations. Existing estimates of locations were noted to be systematically biased in NNE by ~30 km along BTFZ and most depth estimates are at 10km. The Cascadia Initiative (CI) and Blanco Transform OBS Experiment deployed 70 and 55 ocean bottom seismometers (OBS), respectively, within the Juan de Fuca (JDF) plate from September 2012 to October 2013. We analysed 19 events M[subscript w] ≥4 as cataloged by regional seismic networks. Regional waveform modeling of three component seismic records was done to obtain earthquake source parameters. We invert for moment tensor, best centroid depth and source time function. Solutions from land only stations are compared against solutions using added offshore stations. We aim to identify biases due to limited coverage on moment tensor. We compare moment tensor solutions obtained by land only and land+OBS. We carry out inversion at a deviatoric constraint on moment tensor with local location estimates. Resolvability of deviatoric and isotropic component of moment tensor source is investigated by changing constraints. Moment tensor is modeled a combination of strike-slip, isotropic and residual CLVD sources whose relative percentages are obtained and analysed. Source mechanisms and magnitudes are compared with ones from Global Centroid Moment Tensor (Global CMT) Catalog, whenever available. Due to the high long-period noise level, OBS data were filtered at 0.05-0.1 Hz, while land data were filtered at 0.02-0.04 Hz. OBS orientations necessary for waveform modeling, were estimated by maximizing the Rayleigh wave cross-correlation between the Hilbert transformed vertical component and trial radial components.
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