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Application of the Paleoseismic Record of Great Cascadia Earthquakes for Use in the 2015 CanadaSHM5 and 2020 CanadaSHM6 Seismic Hazard Models

Session: Earthquake Science, Hazards and Policy in Cascadia [Poster]

Type: Poster

Date: 4/20/2021

Presentation Time: 11:30 AM Pacific

Description: 

The CanadaSHM3 model (used for the1985 National Building Code of Canada, NBCC1985) did not include great Cascadia subduction interface events, but CanadaSHM4 (NBCC2005) added a deterministic model whose values were used for design only if they exceeded the hazard values from other sources. CanadaSHM5 introduced a probabilistic treatment of Cascadia's Juan de Fuca, Explorer and Winona segments for NBCC2015. The 2015 Juan de Fuca rate of great earthquakes was based on the turbidite chronology of Goldfinger et al. (2012 pre-print). Partial, southern ruptures were not included, as being too distant from Canada to contribute significantly. The 2015 analysis used 18 turbidites of a 10,097-year record, giving a mean interval of 532 years and a standard deviation of 234 years. The analysis neglected the possibility of event clustering. The rupture intervals (time since the last earthquake) were turned into magnitudes using fixed rupture length and width together with choices for slip rate and crustal rigidity to give central, upper and lower recurrence rates. Magnitudes were in the range 8.55-9.28. To capture the uncertainty in how close the energy release would be to sites on land, three choices for the down-dip extent of the rupture For CanadaSHM6 our interpretation of Goldfinger et al.’s 2017 updated turbidite history adds 4 events off Washington to decrease the mean interval to 434 years and reduce the standard deviation to 164 years; the events now appear more regular than clustered. The interface model was combined with crustal and inslab sources to give probabilistic seismic hazard estimates. Considered alone, the 2020 interface rate increased the 2015 seismic hazard estimate by about 9%. Juan de Fuca interface shaking dominates the 2020 design values in Victoria and Vancouver for periods >1 second

Presenting Author: John Adams

Student Presenter: No

Authors