Session 7.3 - Earthquake Case Histories and Instrumental Measures  

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Caracus Earthquake, 1967, Revisited

R.I. Skinner

This paper examines the types of earthquake damage which occurred throughout and near the city of Caracus, Venezuela, in 1967. Attempts were made to deduce the mechanisms of damage and collapse, and their causes. The character of the earthquake motions were estimated, and included large microzone effects due to varying depths of alluvium throughout the city, and a very severe ground lurch towards the north at the Macuto Beach resort. New Zealand responses to lessons from the Caracus earthquake are discussed. A more detailed account is given in the author’s original report (Skinner 1968).

Paper 080: [Read] [Print]

Keywords: microzones, near-fault pulses, engineering studies, matched buildings

Modeling Magnitude Distribution for Local Hazard Evaluation: A New Approach

G. Grandori, E. Guagenti and L. Petrini

For the design of ordinary buildings, many seismic codes prescribe to assume the peak ground acceleration corresponding to a return period of the order of 500 years at the site, a(500). This quantity is dominated by the size distribution of strong earthquakes that are expected in the zone. On the other hand, the number of strong earthquakes in available catalogs is generally not sufficient for the statistical validation of a magnitude distribution model, nor for a meaningful comparison between competing models. Besides this epistemic uncertainty, the problem is obviously affected by the inevitable statistical uncertainty due to the fact that the catalog is a random sample drawn from the real magnitude distribution (in the favourable hypothesis that such a distribution exists). In this paper we give a definition of the credibility of a magnitude distribution model as regards the evaluation of a(500) at a specific site. We find that the comparison between the credibilities of competing models opens new statistical prospects. In particular the hazard analysis for an Italian site shows that the systematic application of the concept of model credibility may lead to a reduction of both statistical and epistemic uncertainty.

Paper 025: [Read] [Print]

Keywords: validation, statistical uncertainty, epistemic uncertainty

Instrumental Measures of Earthquake Intensity in New Zealand.

P.N. Davenport

The economic and societal impact of an earthquake on the built environment is often related to the shaking intensity that is expressed on the Modified Mercalli Intensity scale (MMI). This measure of intensity is determined by observers present during the event or by evidence (usually damage) that can be seen later. Compiling MMI values from observations can be a time consuming task and the information may not be available until some considerable delay after an earthquake.

With the recent deployment of telemetered strong motion instruments throughout New Zealand, it is desirable to be able to rapidly estimate the shaking level intensity from the strong motion records that are available shortly after an earthquake event.

A pilot study found that no single parameter from the strong motion records appears to be a good analogue, by itself, of MMI. This paper reports a more detailed study of the available data and the numerical results determined for a correlation of the MMI values with a number of strong motion parameters such as peak accelerations, velocities, displacements and spectra as well as other derived values.

Paper 071: [Read] [Print]

Theoretical Design and Field Deployment of a Dense Strong Motion Instrument Network for the Alpine Fault, South Island, New Zealand.

C. Francois, J.B. Berrill and J.R. Pettinga

A dense network of strong motion seismometers is being developed for the central South Island of New Zealand. This is to investigate the complexities of the upper crustal rupture process and propagation of major seismogenic sources such as the Alpine Fault and strands of the Marlborough Fault System defining the South Island sector of the Australia-Pacific plate boundary zone.

The proposed network is designed as a dense array of approximately 20 accelerographs using the University of Canterbury 12-bit CUSP instrument, whose development is now nearing completion. It will be deployed immediately to the East of the East-dipping Alpine Fault in the central West Coast region of the South Island, and coverage will extend across the to the Alpine-Hope Fault junction region.

The array layout is being designed utilizing the frequency-analysis MUSIC method (Multiple Signal Characterization) developed by Goldstein and Archuleta (1991a&b). Synthetic strong-motion records were computed using an empirical Green's function synthetic seismogram program EMPSYN (Hutchings, 1987). The process of finding an optimal configuration is dependent on the geometry of the array (study of the frequency analysis performance of the modelled earthquake data for various proposed array configurations), and on the instrument site conditions (geology, communications, accessibility, isolation etc).

Paper 136: [Read] [Print]

Keywords: Alpine Fault, fault rupture process, dense arrays

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