BeckerFraserPhotos December 2011 photograph 0079

Images, UC QuakeStudies

A tribute taped to a window of a house on Tasman Place. The tribute reads, "Our red zoned house. When we bought you years ago, you looked a bit tired and sad, but overall you weren't too bad. We spruced you up with paint and love and asked for a blessing from above. The years went by, family and friends celebrations under your roof, your 'veggie' garden gave us kai. We felt safe within your wall, then one dreadful September night, the shaking earth made you fall. You tried with all your groaning might to keep us from harm. Because you were strongly built we held onto the door, while a wave of terror buckled the floor and outside the garden flooded with silt. Now you are near the end, sunken walls and windows bend. We say goodbye today and let you go, Our spirit and heart feels low. You are more than just mortar and brick. For us you were a gift, a safe haven where we once lived".

What caused the spatial variability of strong ground motions near the epic…

Research papers, University of Canterbury Library

During the 2011 M7.8 Kaikōura earthquake, ground motions recorded near the epicentre showed a significant spatial variation. The Te Mara farm (WTMC) station, the nearest to the epicentre, recorded 1g and 2.7g of horizontal and vertical peak ground accelerations (PGA), respectively. The nearby Waiu Gorge (WIGC) station recorded a horizontal PGA of 0.8g. Interestingly, however, the Culverden Airlie Farm (CULC) station that was very closely located to WIGC recorded a horizontal PGA of only 0.25g. This poster demonstrates how the local geological condition could have contributed to the spatially variable ground motions observed in the North Canterbury, based on the results of recently conducted geophysical investigations. The surficial geology of this area is dominated by alluvial gravel deposits with traces of silt. A borehole log showed that the thickness of the sediments at WTMC is over 76 metres. Interestingly, the shear wave velocity (Vs) profiles obtained from the three strong motion sites suggest unusually high shear wave velocity of the gravelly sediments. The velocity of sediments and the lack of clear peaks in the horizontal-to-vertical (H/V) spectral ratio at WTMC suggest that the large ground motion observed at this station was likely caused by the proximity of the station to the causative fault itself; the site effect was likely insignificant. Comparisons of H/V spectral ratios and Vs profiles suggest that the sediment thickness is much smaller at WIGC compared with CULC; the high PGA at WIGC was likely influenced by the high-frequency amplification caused by the response of shallow sediments.