Search

found 486 results

Images for Physics; more images...

Images, UC QuakeStudies

A photograph of Graeme Kershaw, Technician at the University of Canterbury Department of Physics and Astronomy, looking through the lens of the Townsend Telescope. The lens is the most crucial component of the telescope. It was found unscratched and unbroken in the rubble of the Observatory tower, after 22 February 2011 earthquake. This means that the telescope can be restored. Other parts of the earthquake-damaged telescope are in the background of the photograph.

Images, UC QuakeStudies

A photograph of Graeme Kershaw, Technician at the University of Canterbury Department of Physics and Astronomy, looking through the lens of the Townsend Telescope. The lens is the most crucial component of the telescope. It was found unscratched and unbroken in the rubble of the Observatory tower, after 22 February 2011 earthquake. This means that the telescope can be restored. Other parts of the earthquake-damaged telescope are in the background of the photograph.

Research papers, University of Canterbury Library

The overarching goal of this dissertation is to improve predictive capabilities of geotechnical seismic site response analyses by incorporating additional salient physical phenomena that influence site effects. Specifically, multidimensional wave-propagation effects that are neglected in conventional 1D site response analyses are incorporated by: (1) combining results of 3D regional-scale simulations with 1D nonlinear wave-propagation site response analysis, and (2) modelling soil heterogeneity in 2D site response analyses using spatially-correlated random fields to perturb soil properties. A method to combine results from 3D hybrid physics-based ground motion simulations with site-specific nonlinear site response analyses was developed. The 3D simulations capture 3D ground motion phenomena on a regional scale, while the 1D nonlinear site response, which is informed by detailed site-specific soil characterization data, can capture site effects more rigorously. Simulations of 11 moderate-to-large earthquakes from the 2010-2011 Canterbury Earthquake Sequence (CES) at 20 strong motion stations (SMS) were used to validate simulations with observed ground motions. The predictions were compared to those from an empirically-based ground motion model (GMM), and from 3D simulations with simplified VS30- based site effects modelling. By comparing all predictions to observations at seismic recording stations, it was found that the 3D physics-based simulations can predict ground motions with comparable bias and uncertainty as the GMM, albeit, with significantly lower bias at long periods. Additionally, the explicit modelling of nonlinear site-response improves predictions significantly compared to the simplified VS30-based approach for soft-soil or atypical sites that exhibit exceptionally strong site effects. A method to account for the spatial variability of soils and wave scattering in 2D site response analyses was developed and validated against a database of vertical array sites in California. The inputs required to run the 2D analyses are nominally the same as those required for 1D analyses (except for spatial correlation parameters), enabling easier adoption in practice. The first step was to create the platform and workflow, and to perform a sensitivity study involving 5,400 2D model realizations to investigate the influence of random field input parameters on wave scattering and site response. Boundary conditions were carefully assessed to understand their effect on the modelled response and select appropriate assumptions for use on a 2D model with lateral heterogeneities. Multiple ground-motion intensity measures (IMs) were analyzed to quantify the influence from random field input parameters and boundary conditions. It was found that this method is capable of scattering seismic waves and creating spatially-varying ground motions at the ground surface. The redistribution of ground-motion energy across wider frequency bands, and the scattering attenuation of high-frequency waves in 2D analyses, resemble features observed in empirical transfer functions (ETFs) computed in other studies. The developed 2D method was subsequently extended to more complicated multi-layer soil profiles and applied to a database of 21 vertical array sites in California to test its appropriate- ness for future predictions. Again, different boundary condition and input motion assumptions were explored to extend the method to the in-situ conditions of a vertical array (with a sensor embedded in the soil). ETFs were compared to theoretical transfer functions (TTFs) from conventional 1D analyses and 2D analyses with heterogeneity. Residuals of transfer-function- based IMs, and IMs of surface ground motions, were also used as validation metrics. The spatial variability of transfer-function-based IMs was estimated from 2D models and compared to the event-to-event variability from ETFs. This method was found capable of significantly improving predictions of median ETF amplification factors, especially for sites that display higher event-to-event variability. For sites that are well represented by 1D methods, the 2D approach can underpredict amplification factors at higher modes, suggesting that the level of heterogeneity may be over-represented by the 2D random field models used in this study.

Research papers, University of Canterbury Library

A major hazard accompanying earthquake shaking in areas of steep topography is the detachment of rocks from bedrock outcrops that subsequently slide, roll, or bounce downslope (i.e. rockfalls). The 2010-2011 Canterbury earthquake sequence caused recurrent and severe rockfall in parts of southern Christchurch. Coseismic rockfall caused five fatalities and significant infrastructural damage during the 2011 Mw 6.2 Christchurch earthquake. Here we examine a rockfall site in southern Christchurch in detail using geomorphic mapping, lidar analysis, geochronology (cosmogenic 3He dating, radiocarbon dating, optically stimulated luminescence (OSL) from quartz, infrared stimulated luminescence from K-feldspar), numerical modeling of rockfall boulder trajectories, and ground motion prediction equations (GMPEs). Rocks fell from the source cliff only in earthquakes with interpolated peak ground velocities exceeding ~10 cm/s; hundreds of smaller earthquakes did not produce rockfall. On the basis of empirical observations, GMPEs and age chronologies we attribute paleo-rockfalls to strong shaking in prehistoric earthquakes. We conclude that earthquake shaking of comparable intensity to the strongest contemporary earthquakes in Christchurch last occurred at this site approximately 5000 to 7000 years ago, and that in some settings, rockfall deposits provide useful proxies for past strong ground motions.

Research papers, University of Canterbury Library

This paper summarizes the development of a high-resolution surficial shear wave velocity model based on the combination of the large high-spatial-density database of cone penetration test (CPT) logs in and around Christchurch, New Zealand and a recently-developed Christchurch-specific empirical correlation between soil shear wave velocity and CPT. This near-surface shear wave velocity model has applications for site characterization efforts via the development of maps of time-averaged shear wave velocities over specific depths, as well as use in site response analysis and ground motion simulation.

Research papers, University of Canterbury Library

he strong motion station at Heathcote Valley School (HVSC) recorded unusually high peak ground accelerations (2.21g vertical and 1.41g horizontal) during the February 2011 Christchurch earthquake. Ground motions recorded at HVSC in numerous other events also exhibited consistently higher intensities compared with nearby strong motion stations. We investigated the underlying causes of such high intensity ground motions at HVSC by means of 2D dynamic finite element analyses, using recorded ground motions during the 2010-2011 Canterbury earthquake sequence. The model takes advantage of a LiDAR-based digital elevation model (DEM) to account for the surface topography, while the geometry and dynamic properties of the surficial soils are characterized by seismic cone penetration tests (sCPT) and Multi-Channel Analyses of Surface Waves (MASW). Comparisons of simulated and recorded ground motions suggests that our model performs well for distant events, while for near-field events, ground motions recorded at the adopted reference station at Lyttelton Port are not reasonable input motions for the simulation. The simulations suggest that Rayleigh waves generated at the inclined interface of the surficial colluvium and underlying volcanic rock strongly affect the ground motions recorded at HVSC, in particular, being the dominant contributor to the recorded vertical motions.

Research papers, University of Canterbury Library

Recent field investigations were carried out to define the shear wave velocity (VS) profile and site periods across the Canterbury region, supplementing earlier efforts in urban Christchurch. Active source surface wave testing, ambient wave field (passive) and H/V spectral ratio methods were used to characterise the soil profile in the region. H/V spectral ratio peaks indicate site periods in the range of 5-7 seconds across much of the Canterbury Plains, broadly consistent with those based on a 1D velocity model for the region. Site periods decrease rapidly in the vicinity of the Canterbury foothills and the Banks Peninsula outcrops. In Christchurch, the Riccarton Gravels result in a significant mode of vibration that has a much shorter period than the site period of the entire soil column down to basement rock.

Research papers, University of Canterbury Library

During the 2010 - 2011 Canterbury earthquake sequence, extensive liquefaction was observed in many areas of Christchurch city and its surroundings, causing widespread damage to buildings and infrastructure. While existing simplified methods were found to work well in some areas of the city, there were also large areas where these methods did not perform satisfactorily. In some of these cases, researchers have proposed that layers of fine grained material within the soil profile may be responsible for preventing the manifestation of liquefaction. This paper presents preliminary findings on the mechanisms at play when pressure differentials exist across a clay layer. It is found that if the clay layer is unable to distort, then pore fluid is unable to break-through the layer even with relatively high pressures, resulting in dissipation of excess pore pressures by seepage. If the layers are however able to distort, then it is possible for the pore fluid to break through the clay layer, potentially resulting in adverse effects in terms of the severity of liquefaction.

Images, UC QuakeStudies

A photograph of the Townsend Telescope in the Observatory at the Christchurch Arts Centre. In the bottom right-hand corner of the photograph is a pulley for the telescope's clock drive. This is one of the pieces that went missing when the Observatory tower collapsed in the 22 February 2011 earthquake. This image was used by Graeme Kershaw, Technician at the University of Canterbury Department of Physics and Astronomy, to identify the telescope's parts after the 22 February 2011 earthquake.

Images, UC QuakeStudies

A photograph of the rubble of the Observatory tower in the South Quad of the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake. A digger was used to clear the rubble away from the building. In the foreground is Chris Whitty, Site Manager of the Christchurch Arts Centre.

Images, UC QuakeStudies

A photograph of the largest section of the Townsend Telescope recovered from the rubble of the Observatory tower. The telescope was housed in the tower at the Christchurch Arts Centre. It was severely damaged when the tower collapsed during the 22 February 2011 earthquake.

Images, UC QuakeStudies

A photograph of the rubble from the Observatory tower in the South Quad of the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake. A digger was used to clear the rubble away from the building. Scaffolding constructed around the tower has also collapsed and is amongst the rubble. A car and the bumper of another car can be seen under the rubble.

Images, UC QuakeStudies

A photograph of the rubble of the Observatory tower in the South Quad of the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake. A digger was used to clear the rubble away from the building. Scaffolding constructed around the tower has also collapsed and is amongst the rubble. In the background is the damaged tower with a tarpaulin draped over the top.

Images, UC QuakeStudies

A photograph of the rubble from the Observatory tower in the South Quad of the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake. A digger was used to clear the rubble away from the building. Scaffolding constructed around the tower has also collapsed and is amongst the rubble. The roof of the tower and a ladder can also be seen.

Images, UC QuakeStudies

A photograph of the base of the Townsend Telescope, still attached to a piece of rubble. The rubble is from the Observatory tower at the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake and the rubble spilled into the courtyard in front. A digger was used to clear the rubble away from the building.

Images, UC QuakeStudies

A photograph of the earthquake damage to the Observatory tower at the Christchurch Arts Centre. The top two storeys of the tower collapsed during the 22 February 2011 earthquake and the rubble spilled into the courtyard in front. A digger was used to clear the rubble away from the building. A tarpaulin has been draped over the top of the tower and the roof of the building behind.

Images, UC QuakeStudies

A photograph of the earthquake damage to the Observatory tower at the Christchurch Arts Centre. The top two storeys of the tower collapsed during the 22 February 2011 earthquake and the rubble spilled into the courtyard in front. A digger was used to clear the rubble away from the building. A tarpaulin has been draped over the top of the broken tower and the roof behind.

Images, UC QuakeStudies

A photograph of the earthquake damage to the Observatory tower at the Christchurch Arts Centre. The top two storeys of the tower collapsed during the 22 February 2011 earthquake and the rubble spilled into the courtyard in front. A digger was used to clear the rubble away from the building. A tarpaulin has been draped over the top of the broken tower and the roof behind.

Images, UC QuakeStudies

A photograph of an earthquake-damaged suitcase in the South Quad of the Christchurch Arts Centre. The suitcase is resting on a pile of scaffolding which had been constructed around the Observatory tower. The scaffolding collapsed along with the tower during the 22 February 2011 earthquake.

Images, UC QuakeStudies

A photograph of the rubble of the Observatory tower in the South Quad of the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake. Scaffolding constructed around the tower has also collapsed and is amongst the rubble.

Images, UC QuakeStudies

A photograph of the rubble of the Observatory tower in the South Quad of the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake. A digger was used to clear the rubble away from the building.

Images, UC QuakeStudies

A photograph of the rubble of the Observatory tower in the South Quad of the Christchurch Arts Centre. The tower collapsed during the 22 February 2011 earthquake and a digger was used to clear the rubble away from the building. Scaffolding constructed around the tower has also collapsed and is amongst the rubble. In the background is the damaged tower with a tarpaulin draped over the top.

Images, UC QuakeStudies

A close-up photograph of parts of the Townsend Telescope recovered from the rubble of the Observatory tower. The telescope was housed in the tower at the Christchurch Arts Centre. It was severely damaged when the tower collapsed during the 22 February 2011 earthquake.

Images, UC QuakeStudies

A photograph of the earthquake-damaged Observatory tower at the Christchurch Arts Centre. The photograph was taken using a cellphone camera. The top of the tower collapsed during the 22 February 2011 earthquake. The rubble from the tower has been cleared and a tarpaulin has been placed over the top of the broken tower. Tyres have been placed on the tarpaulin to hold it down. A temporary roof has also been constructed over the tower to keep out the rain. Two vehicles are parked in front.