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Images, UC QuakeStudies

Detail of the partially-demolished Henry Africa's building. The photographer comments, "A building housing a restaurant and a great little neighbourhood bar is finally coming down because of earthquake damage. Henry's doorway. Still standing - the zebra striped doorway into Henry Africa's".

Images, eqnz.chch.2010

Open for business. Photos taken in Diamond Harbour Library on May 24, 2011 following the February 22 earthquake. File reference: CCL-2011-05-24-Diamond Harbour-After-The-Earthquake-IMG_15 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Lyttelton is a one dog library today. Photos taken in Lyttelton Library on May 24, 2011 following the February 22 earthquake. File reference: CCL-2011-05-24-Lyttelton-After-The-Earthquake-IMG_20 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Plenty to choose from at Redwood Library. Photos taken in Redwood Library on April 8 following the February 22 earthquake. File reference: CCL-2011-04-08-Redwood-After-The-Earthquake-IMG_0441 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Photos taken in Parklands Library on March 31 following the February 22 earthquake. File reference: CCL-2011-03-31-New Brighton-After-The-Earthquake-NB Parkland 019 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Photos taken in Parklands Library on March 31 following the February 22 earthquake. File reference: CCL-2011-03-31-New Brighton-After-The-Earthquake-NB Parkland 017 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Absorbed in preschool storytime. Photos taken in Diamond Harbour Library on May 24, 2011 following the February 22 earthquake. File reference: CCL-2011-05-24-Diamond Harbour-After-The-Earthquake-IMG_21 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Interesting to look up at Redwood. Photos taken in Redwood Library on April 8 following the February 22 earthquake. File reference: CCL-2011-04-08-Redwood-After-The-Earthquake-IMG_0440 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Propped up neighbours but life goes one. Photos taken in Lyttelton Library on May 24, 2011 following the February 22 earthquake. File reference: CCL-2011-05-24-Lyttelton-After-The-Earthquake-IMG_15 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Plenty to choose from at Redwood Photos taken in Redwood Library on April 8 following the February 22 earthquake. File reference: CCL-2011-04-08-Redwood-After-The-Earthquake-IMG_0444 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Photos taken in Lyttelton showing the demolition of various buildings following the February 22 earthquake. File reference: CCL-2011-05-20-Lyttelton-Demolition-P1120461 From the collection of Christchurch City Libraries.

Images, eqnz.chch.2010

Photos taken in New Brighton on March 31 following the February 22 earthquake. File reference: CCL-2011-03-25-New Brighton-After-The-Earthquake-NB Parkland 004 From the collection of Christchurch City Libraries

Images, eqnz.chch.2010

Photos taken at the Lyttelton Community briefing held on March 7 2011 following the magnitude 6.3 earthquake on 22 February 2011. File Ref: CCL-2011-03-07-Lyttelton-Community-Briefing-P1110622 From the collection of Christchurch City Libraries.

Images, eqnz.chch.2010

Photos taken at the Lyttelton Community briefing held on March 7 2011 following the magnitude 6.3 earthquake on 22 February 2011. File Ref: CCL-2011-03-07-Lyttelton-Community-Briefing-P1110619 From the collection of Christchurch City Libraries.

Images, eqnz.chch.2010

Neighbours across the river showing earthquake damage. Hotel Grand Chancellor in the background. File reference: CCL-2011-08-12-CanterburyPublic Library pre-demolition-044 From the collection of Christchurch City Libraries.

Research papers, University of Canterbury Library

Damage distribution maps from strong earthquakes and recorded data from field experiments have repeatedly shown that the ground surface topography and subsurface stratigraphy play a decisive role in shaping the ground motion characteristics at a site. Published theoretical studies qualitatively agree with observations from past seismic events and experiments; quantitatively, however, they systematically underestimate the absolute level of topographic amplification up to an order of magnitude or more in some cases. We have hypothesized in previous work that this discrepancy stems from idealizations of the geometry, material properties, and incident motion characteristics that most theoretical studies make. In this study, we perform numerical simulations of seismic wave propagation in heterogeneous media with arbitrary ground surface geometry, and compare results with high quality field recordings from a site with strong surface topography. Our goal is to explore whether high-fidelity simulations and realistic numerical models can – contrary to theoretical models – capture quantitatively the frequency and amplitude characteristics of topographic effects. For validation, we use field data from a linear array of nine portable seismometers that we deployed on Mount Pleasant and Heathcote Valley, Christchurch, New Zealand, and we compute empirical standard spectral ratios (SSR) and single-station horizontal-to-vertical spectral ratios (HVSR). The instruments recorded ambient vibrations and remote earthquakes for a period of two months (March-April 2017). We next perform two-dimensional wave propagation simulations using the explicit finite difference code FLAC. We construct our numerical model using a high-resolution (8m) Digital Elevation Map (DEM) available for the site, an estimated subsurface stratigraphy consistent with the geomorphology of the site, and soil properties estimated from in-situ and non-destructive tests. We subject the model to in-plane and out-of-plane incident motions that span a broadband frequency range (0.1-20Hz). Numerical and empirical spectral ratios from our blind prediction are found in very good quantitative agreement for stations on the slope of Mount Pleasant and on the surface of Heathcote Valley, across a wide range of frequencies that reveal the role of topography, soil amplification and basin edge focusing on the distribution of ground surface motion.