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Characterizing the Cascadia Subduction Zone for Seismic Hazard Assessments

By Ivan Wong1, Ram Kulkarni1, Judith Zachariasen1, Martin Lawrence2, Kathryn Hanson3, Robert Youngs3, John Clague4, Dean Ostenaa5, Roland LaForge5, Martin McCann6

1. URS Corporation 2. BC Hydro 3. AMEC 4. Simon Fraser University 5. Fugro Consultants 6. Jack R. Benjamin & Associates

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Abstract

Characterizing the Cascadia Subduction Zone for Seismic Hazard Assessments

As part of the BC Hydro PSHA project, a new seismic source model of the Cascadia subduction zone (CSZ) was developed using a logic tree approach. The most significant CSZ seismic source parameters are; the location of the eastern edge of the megathrust rupture zone, rupture zone segmentation, the northern limit of rupture, recurrence models, recurrence intervals and maximum magnitudes. The eastern rupture extent is adapted from the model of Wang and Hyndman (2011), with alternative M 9 rupture scenarios extending down to (1) the base of the coseismic transition zone (CTZ), (2) 30 km downdip, and (3) 10 km updip of the base of the CTZ. The up-dip extent of recorded episodic tremor and slip (ETS) events was considered in the weighting of the three scenarios. Three possible modes of rupture for the megathrust are considered: (1) full-length rupture events around M 9; (2) intermediate-sized earthquakes of M 8 to 8.8, which rupture one or two possible segments in the southern half of the subduction zone; and (3) smaller earthquakes of M < 8 randomly spatially located along the length of the CSZ. Segmentation of the Cascadia subduction zone is based on the model of Goldfinger et al. (2012), and paleoseismic evidence that supports full rupture events, and intermediate magnitude earthquakes along the central and southern segments. There is very little evidence for intermediate-sized earthquakes in the northern portion of the CSZ and smaller earthquakes along the length of the CSZ with the possible exception of the 1992 M 7.2 Cape Mendocino earthquake. Alternative rupture scenarios with and without the Explorer plate in CSZ ruptures is included in the model. Time-independent and time-dependent recurrence intervals are estimated for full rupture events based on the Holocene turbidite history of Goldfinger et al. (2012). Temporal clustering of M 9 earthquakes is addressed by including inter-cluster and intra-cluster recurrence intervals. Only time-independent recurrence intervals are estimated for the two southern rupture scenarios. The sensitivities of the calculated hazard to the rupture scenarios and recurrence model indicate the most significant impact on the hazard is due to the uncertainty in full-rupture M 9 recurrence intervals.

Cite this work

Researchers should cite this work as follows:

  • Ivan Wong; Ram Kulkarni; Judith Zachariasen; Martin Lawrence; Kathryn Hanson; Robert Youngs; John Clague; Dean Ostenaa; Roland LaForge; Martin McCann (2014). "Characterizing the Cascadia Subduction Zone for Seismic Hazard Assessments", Network for Earthquake Engineering Simulation (distributor), Paper, DOI:10.4231/D3BC3SX94
  • Ivan Wong; Ram Kulkarni; Judith Zachariasen; Martin Lawrence; Kathryn Hanson; Robert Youngs; John Clague; Dean Ostenaa; Roland LaForge; Martin McCann (2014), "Characterizing the Cascadia Subduction Zone for Seismic Hazard Assessments," http://nees.org/resources/12159.

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