Modelling bonus seismic wave arrivals recorded on SchoolShake seismographs from the March 2025 Orcas Island earthquake
| dc.contributor.author | Reed, Sedona | |
| dc.date.accessioned | 2026-05-07T15:35:20Z | |
| dc.date.available | 2026-05-07T15:35:20Z | |
| dc.date.issued | 2026 | |
| dc.description.abstract | In the seismograms recorded at SchoolShake network seismographs across Greater Victoria, BC during the M4.5 Orcas Island earthquake on March 3rd, 2025, a bonus wave arrival was identified between the P and S arrivals at stations within an azimuthal range of 219-256° around the epicenter. Such arrivals had not been previously documented. The focus of this study was to determine the origin of the bonus seismic wave arrivals using seismic ray path and travel time modelling for increasing levels of model complexity. Initial modelling using the 1-D ObsPy.TauPy software successfully reproduced direct P and S wave arrivals but was insufficient to model the bonus phase arrivals. Subsequent 2-D modelling using Pykonal was implemented to better account for the subsurface structure, which includes dipping boundaries such as the top of the subducting Juan de Fuca plate. This modelling demonstrated that a reflection of seismic energy off the Juan de Fuca slab produced arrivals too late to match the bonus arrivals, therefore ruling out this boundary as their origin. Modelling reflections off a shallower boundary, consistent with the highly seismically reflective E-layer, produced arrival times consistent with the actual bonus phase arrivals. Residuals between the observed and modelled arrival times were minimized to lie within ±0.8 seconds across the analyzed stations, providing evidence that the bonus arrivals are consistent with P wave energy reflection off the top of the E-layer. These findings demonstrate the need for more spatially complex subsurface models, such as the 2-D Pykonal model and ideally a 3-D model, to model seismic wave travel in the presence of dipping subsurface boundaries. The bonus phase arrivals may contribute to longer and more intense shaking, which highlights the importance of understanding seismic wave travel to improve local hazard assessment and risk mitigation in Greater Victoria. Supervisors: Camille Brillon and Lucinda Leonard | |
| dc.description.scholarlevel | Undergraduate | |
| dc.identifier.uri | https://hdl.handle.net/1828/23811 | |
| dc.language.iso | en | |
| dc.subject | earthquake | |
| dc.subject | Cascadia | |
| dc.subject | subduction zone | |
| dc.subject | SchoolShake | |
| dc.subject | P waves | |
| dc.subject | seismic ray modelling | |
| dc.subject | shaking intensity | |
| dc.subject.department | School of Earth and Ocean Sciences | |
| dc.title | Modelling bonus seismic wave arrivals recorded on SchoolShake seismographs from the March 2025 Orcas Island earthquake | |
| dc.type | Honours thesis |