Frederick Jackson Supervisor Dr Sheri Molnar 2 Population gt 2 million and critical infrastructure Hazard 3 types of earthquakes sedimentary basin What will ground shaking be like during a future large earthquake ID: 1034579
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1. Earthquake Site Characterization in Metropolitan VancouverFrederick JacksonSupervisor – Dr. Sheri Molnar
2. 2Population > 2 million and critical infrastructureHazard 3 types of earthquakessedimentary basin What will ground shaking be like during a future large earthquake? Georgia basinGreater Vancouver is area of highest seismic risk in Canada
3. Earthquake Ground ShakingDepends on: Earthquake source (mechanism) and depthMaterial properties along travel pathSite conditionsGround surface shaking is strongly affected by waves travelling through upper few kilometers (or less)Earthquake damage related to “soft” soils (i.e. low shear-wave velocity material)1964 Alaska, 1985 Mexico City, 1989 Loma Prieta, 1994 Northridge, 1995 Kobe Sedimentary basin (3D structure)Soil profile(1D structure)
4. Application of Seismic Microzonation MapsExample from 1989 Loma Prieta Earthquake in California: Areas of greater hazard identified on maps as early as 1975Source uncertain
5. Seismic Soil Hazard Mapping: Work done to date in the Lower MainlandSoil hazard (amplification) map of Lower Mainland prepared for BC School Retrofit program by UBCMonahan, 2005Regional map based on surficial geology, limited borehole data, and regional shear-wave velocity model
6. Project AimsAdd to the database of knowledge on seismic velocities in Metropolitan Vancouver as part of seismic microzonation mapping project of the regionImproved site classification and hazard assessment
7. ObjectivesUpdate and assess earthquake site response in Metropolitan Vancouver Earthquake recordings from December 2015 M4.7 Victoria earthquakePerform site characterization at ~15 “new” locations in Metropolitan Vancouver School sites in Metropolitan Vancouver: (1) BC School Seismic Retrofit program, (2) UBC-RCAV Earthquake Early Warning System
8. 1. Ground motion from the December 2015 Earthquake (M4.7)Assess whether ground motions amplified by local geologyFor example, amplitudes (PGA) should reduce with distance but ‘pockets’ of anomalous amplitudeAmplification depends on:Thickness and elastic properties of the upper soil layers (>1km)Seismic impedence ratioM=4.7Strait of GeorgiaGreater Vancouver VictoriaBritish ColumbiaVancouver Island
9. 2. Site CharacterizationPredict how earthquake ground motions may be altered by underlying geology (amplitude, frequency, duration) a) Spectral Ratio MethodsEarthquake and microtremor horizontal-to-vertical spectral ratios Provide estimates of site period or peak frequencyb) Shear Velocity Depth ProfilingPassive seismic (microtremor) arraysProvide estimates of Vs30 (NBCC requirement)
10. a) Spectral Ratio MethodsSingle three-component sensorsCharacterise sites using the spectral ratio between horizontal and vertical components of motion (H/V)Ratios exhibit a maximum peak corresponding to the fundamental resonance frequency‘Growth’ of peaks towards surface = site amplificationFrequency
11. b) Array TechniquesMultiple sensors placed in a geometric arrayCan use the dispersive nature of Rayleigh waves to generate a dispersion curve This can be inverted to obtain a shear wave velocity profileFrequency (Hz)Frequency (Hz)Velocity (m/s)Velocity (m/s)
12. Impact of studyNon-invasive, rapid, and inexpensive earthquake site characterizationImproved estimates of shear wave velocity within Metropolitan Vancouver for use in:Assessment of amplification and liquefaction potentialSeismic design; building and bridge codesImproved hazard estimates Improved risk (loss) estimates
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