Session 1 Session 2 Session 3 Session 4 Session 5 Session 6 Posters 

Short-term probabilistic aftershock hazard mapping

M.C. Gerstenberger, S. Wiemer and L.M. Jones

We estimate the short-term hazard associated with strong earthquake shaking by combining the existing time-independent New Zealand hazard model with models describing the time-dependent hazard associated with earthquake clustering. We start with a generic New Zealand time-dependent kernel based on the Reasenberg and Jones aftershock model and automatically incorporate increasingly complex spatial models. By using the corrected Akaike Information Criterion, we combine all models and create a single forecast. An analogous model is currently operating in California; it produces in real-time forecasts of the probability of exceeding Modified Mercalli Intensity VI within the next 24 hours; the maps are automatically updated and available via the web. We have tested the California model using likelihood based statistical methods and determined that the model cannot be rejected and that the forecasts are improved by adding spatial complexity.

Paper P35: [Read]

Low-technology techniques for seismic isolation

H. Xiao, J.W. John and T. Tam

This project sought to improve the seismic performance of low-rise buildings by the introduction of a simple, low cost seismic isolation system at the time of construction, or re-construction. The main advantage of the friction sliding isolation layer is that the seismic base shear force transmitted from the ground to the isolated structure can be controlled at the level of the friction force in the sliding layer. This project tested five potential isolation materials for their frictional features by both semi-dynamic and dynamic shake table experiments. The materials were sand, lighting ridge pebble, polypropylene and PVC sheet and polythene membrane. The isolation effect levels of the materials serving as the sliding layer were obtained from the experimental results. Three computer models, using Working Model 2D, Nonlin and SAP2000, were developed to simulate the sliding system. Attempts were also made to verify the validity of the seismic performance of the system theoretically solving the equations of motion for both single-degree-of-freedom and two-degree-of-freedom sliding system.

Paper P36: [Read]

Explosion-induced structural response: An overview

R.P. Dhakal

This paper presents a conceptual discussion on structural response to ground shocks. Nonlinear finite element analyses on a 2-storey RC frame subjected to explosion-induced ground shocks are carried out to investigate structural response to explosions. This study shows that maximum response to explosion generally occurs after the major ground shock has ceased. It is found that the response in the forced-vibration phase includes high frequency vibration modes characterised by small displacement but large acceleration, which induce high inertial shear force. On the other hand, the free-vibration response is dominated by lower frequency oscillations with large displacement which may soften the structure. Hence, a structure subjected to explosion may have to face two probable hazards. Firstly, it may experience a large shear force that may cause a sudden shear failure within the major shock period. Secondly, if its shear resistance is large enough to overcome the induced shear force, it may undergo large flexural deformation that may induce severe damage after the major ground shock has ceased. The possibility and extent of these two damage mechanisms depend on the scale of explosion, the distance of the structure from the explosion source and the toughness of the structure.

Paper P40: [Read]

Beam-column joint tests with grade 500E reinforcing

L.M. Megget, N.J. Brooke and R.C. Fenwick

A database of beam-column joint test results has been assembled and analysed to determine appropriate design drift limits for the prevention of bond failure in reinforced concrete frames. In order to enhance the coverage of the database for units in which higher grade reinforcement with bar diameters in excess of 16mm were used, further beam-column joints have been designed at the University of Auckland using 25 mm beam reinforcement. The result of the first of these tests is reported. Despite not meeting the requirements of the recent amendment to NZS 3101:1995 with respect to column depth, the unit did not exhibit a bond failure in the joint region.

Paper P41: [Read]

Risk reduction in school buildings against earthquake

U.S. Patil

School buildings are having risk from natural earthquake hazards at various places in India and different developing countries. The special attention is made on the risk directly related to the structures and their users in the school, to improve the standards of school buildings in accordance with technical regular issues. School buildings are regularly used for permanent activities carried out by the children to improve performance of human brain. Earthquake risk reduction technique is implemented to prevent the structure of school buildings and construct safer structures, which might be reduce when there is risk of earthquake. Now a day the school buildings are designed and constructed by professionals to achieve the aims and objectives of schools instated of minimizing earthquake hazards.In this paper, the research is concentrated on the seismic risk and the probability of consequences due to occurrences of earthquake. The expected consequences are injury of the students, loss of lives, health, physical damage, property damage, lifeline failures and its effects. In addition, the interruption in the school and loss of society with respect to new generation is minimized because of social, cultural, economy parameters. The paper concludes with the reduction and control of risk to limit the adverse impact of natural hazards on the public education and school buildings.

Paper P42: [Read]

Subsidence in the Lower Hutt Valley and the interplay between Wellington and Wairarapa Fault earthquakes

J.G Begg, R.J. Van Dissen and D.A. Rhoades

In 1855, rupture on the Wairarapa Fault resulted in uplift of 1.2-1.5 m in the Lower Hutt Valley. This historical event has coloured expectations of what will happen in the next major Wellington region earthquake. However, geological data from the Hutt Valley provide compelling evidence that most major earthquakes in the region generate local subsidence rather than uplift.

Long-, intermediate- and short-term records of vertical deformation in the area are consistent in requiring subsidence in the Lower Hutt Valley. Drillhole records reveal alternating cool alluvial and warm marine climatic deposits, and provide data on elevations of paleoshorelines, numerically constraining the rate and shape of medium-term subsidence. The shape and position of the subsidence signal link it to movement on the Wellington Fault.

Long term nett subsidence in the Lower Hutt Valley equals the sum of uplift associated with rupture of the Wairarapa Fault plus subsidence associated with Wellington Fault rupture. Single event subsidence for a Wellington Fault earthquake is calculated to be c. 1 m. Although predominantly a dextral strike-slip fault, the Wellington Fault’s vertical component of displacement is a very important contribution to hazard, particularly in areas of low relief near sea level.

Paper P43: [Read]

Design and development of a low-cost, high-performance, strong-motion accelerograph

H.R. Avery, J.B. Berrill and M.B. Dewe

This paper outlines the conception, design and development of the CUSP accelerograph system. The CUSP accelerograph provides a cheap strong-motion specific instrument that fulfils the requirements of the earthquake engineering community without the high cost penalty associated with purchasing the unwanted resolution of a sensitive seismograph.

Paper P44: [Read]

A seismic site response and ground-shaking hazard assessment for Blenheim, New Zealand

E. de J. Robertson and E.G.C. Smith

Portable seismographs were operated at 8 sites in and near Blenheim, one serving as a reference for comparison of site response from small local and regional earthquakes.

Some resonance was observed at three sites, but there were no common resonant frequencies. Most sites exhibited mean amplifications of 1 – 2 times the signal at the reference site. Average amplifications at the resonant frequencies were up to six times the reference. It is concluded that there is less variation in site response in Blenheim than in most locations elsewhere in New Zealand that have been investigated in this way.

Blenheim's principal earthquake hazard derives from its close proximity to the Wairau and Awatere faults, and from the slightly more distant Clarence, Kekerengu, Elliot, Jordon and Hope faults of the Marlborough fault system. All are capable of producing earthquakes of M_w 6.9-7.9. The average return time for an earthquake on any one of these is in the range 28-51 years. The average time between an earthquake on either the Wairau or Awatere faults is in the range 350-950 years. An M_w 7.5 earthquake on either could produce peak ground accelerations of up to 1.4g at the sites surveyed, and intensities from MM VII to more than IX.

Paper P45: [Read]

GPS geodetic monitoring in regions of high intra-plate seismic activity in Australia

M. Leonard

The Australian cities of Adelaide and Perth lie in or adjacent to regions of relatively high seismicity, by Australian standards. The seismicity of both areas has had significant temporal and spatial variation over the last century. Despite similar levels of seismic activity the two areas have very different topography, with the Adelaide region being hilly and the Perth region being essentially flat. Knowledge of the deformation rate in these regions will improve our understanding of their long-term seismicity and so an improved estimate of their seismic hazard. To this end, 50 station, GPS geodetic networks have been established in both regions. By global standards the velocities expected are very small (0.2-1.0mm/yr) and are near the limit of current GPS technology. In designing the survey minimising errors was a major focus, with all sites being monuments on hard rock and the occupation period being 7 days. The epoch one data for the Perth network was obtained in May 2002 and the Adelaide network in May 2003. The typical internally estimated precision obtained, for each station in the networks, was 1mm (1σ). Repeat occupations are planned to be at three to four year intervals.

Paper P48: [Read]

Paleoliquefaction studies in Australia to constrain earthquake hazard estimates

C. Collins, P. Cummins, D. Clark, M. Tuttle and R. Van Arsdale

Australia has a low rate of modern seismicity compared to plate margin regions, and a short historical record of earthquakes. These factors combined manifest as significant uncertainty in the Australian earthquake hazard map. One approach to address the problem of sparse historic seismicity in intraplate regions like Australia is to use paleoliquefaction studies to constrain the occurrence of prehistoric earthquakes. Liquefaction was observed following large historic earthquakes in South Australia and Victoria, and numerous ‘sand blows’ were observed following the 1968 Meckering earthquake in Western Australia. It is therefore likely that prehistoric earthquakes in these areas would have also induced liquefaction. Liquefaction deposits might also be anticipated in other areas which are geologically prone to liquefaction, but have not experienced an historical earthquake. Four areas were investigated for paleoliquefaction: (1) southeastern South Australia, the site of pronounced liquefaction associated with a large (Ms 6.5) 1897 earthquake; (2) Meckering the site of the 1968 Ms 6.8 earthquake in the South West Seismic Zone; (3) the Perth region, a major urban centre situated in a large sedimentary basin west of the South West Seismic Zone, and (4) the Goulburn river near the Cadell fault in Victoria, whose banks consist of poorly consolidated fluvial sediments and lie near a large fault which experienced slip in the Quaternary. In this paper we discuss why we have chosen these sites as having high potential for paleoliquefaction studies, and present some results from preliminary surveys at the four target areas.

Paper P50: [Read]

Session 1 Session 2 Session 3 Session 4 Session 5 Session 6 Posters