Regional differences in attenuation modelling for Eastern China

This paper describes the development of seismological models for three sub-regions within Eastern China. An important feature of the modelling is that two main types of local data were used to determine parameters for input into the seismological model. Shear wave velocity data was used in Step One of the procedure for deriving the upper crustal factors which are part of the seismological model. Two further steps were involved in incorporating the historical Intensity (MMI) data into the modelling. In Step Two, the simulated peak ground velocity (PGV) values were converted to MMI values, and site factor was calculated by dividing the inferred PGV value by the respective simulated PGV value for each given (short distance) earthquake scenario. In Step Three, the quality (Q) factor of the seismological model for each sub-region was calibrated in accordance with the criterion that site factors inferred from records of long distance earthquakes in the database match with the median site factor obtained in Step Two for short distance earthquakes. Importantly, the Q values obtained by this calibration method were highly consistent with Coda Q values (obtained for each sub-region from a previous study by Jin and Aki based on analysing records of local earth tremors). The calibrated Q values in combination with the developed crustal factors and geometrical attenuation factor constitute the regional seismological model for Eastern China. The seismological model so developed takes into account intra-regional differences and has been used to simulate strong ground motions by the stochastic method for assessing the potential seismic hazards in the region. © 2010 Elsevier Ltd.postprin

A design spectrum model for flexible soil sites in regions of low-to-moderate seismicity

Design spectrum (DS) models in major codes of practice for structural design of buildings typically stipulate empirical site factors for each of the five, or six, site classes. Although the phenomenon of resonant like amplification behaviour of the structure caused by multiple wave reflections is well known, the potentials for such periodic amplification behaviour are not explicitly considered in code models. This is partly because of expert opinion that such effects are very "localised" in the frequency domain and can be suppressed readily by damping. However, investigations into the risk of collapse of non-ductile, and irregular structural systems, common in regions of low-to-moderate seismicity, revealed the extensive influence of periodic base excitations on flexible soil sites (with initial small-strain natural period T-i > 0.5 s). In this paper, an alternative DS model which addresses the important phenomenon of soil resonance without the need of computational site response analysis of the subsurface model of the site is introduced

Rare earthquake response spectra for typical site conditions in Hong Kong

Hong Kong is located in a region of low-to-moderate seismicity; the potential consequences in the event of a nearby major earthquake should not be underrated. In the past two decades, researchers have conducted many studies on this issue and it is now clear that design procedures should not be directly borrowed from other codes of practice without modifications. This paper aims at presenting the rare earthquake response spectra for typical rock and soil sites in Hong Kong, which form the basis of a seismic design procedure. The uniform hazard spectrum (UHS) for rock sites was obtained from seismic hazard assessment using probabilistic methods. Records from 16 boreholes, representing a wide range of local site conditions, were collected from different locations in Hong Kong. A site-specific response spectrum was then constructed based on the results of site response analyses. Moreover, the 16 site-specific response spectra have been grouped into four types based on the (initial) site natural periods, which allows convenient evaluation of the loading characteristics that are expected at different types of sites. Finally, the rare earthquake response spectra proposed for Hong Kong are compared with those constructed based on the Chinese code (GB) and the Eurocode (EC8).postprin

Site-Dependent Response Spectral Attenuation Modelling

A site-dependent response spectral attenuation model is an important element in a site-dependent seismic hazard assessment. Seismic attenuation behaviour is controlled by a large number of wave modification mechanisms, some of which have characteristics specific to a local area or a particular site, whilst others can be generalised to the entire seismic region. Factors representing these mechanisms are often not resolved. An attenuation modelling approach is demonstrated in this paper, to evaluate individual regional and local wave modification factors. The upper-crust amplification factor computed from the modelled rock shear wave velocity profile was then combined with predicted attenuation parameters to determine the upper-crust modification filter function associated with Singaporean geological formations. Stochastic simulations of the seismological model for the magnitude 9.3 Aceh earthquake (Indonesia) on the 26th of December in 2004, were performed and compared with the response spectra recorded on a rock site in Singapore.link_to_OA_fulltex

Deterministic seismic hazard parameters and engineering risk implications for the Hong Kong region

The paper reviews and compares recent regional studies evaluating the seismic hazard parameters required to assess the seismic risk to engineering construction in the Coastal Region of South China (CRSC) including Hong Kong (HK). The review establishes that the CRSC, and in particular the offshore seismic belt, has mean earthquake magnitude recurrence intervals (MRIs) or return periods that are 2-3 times shorter than those in the eastern United States (EUS), with which the HK region has been compared. An ensemble of realistic design-level earthquake events suitable for defining the regional seismic hazard and for undertaking engineering risk assessment is then formulated, in the form of deterministic magnitude-distance pairs associated with earthquake magnitudes having a range of MRIs, and the significance of the maximum credible earthquake (MCE) magnitude is highlighted. Next, the scenario earthquake events have been used to predict the expected levels of peak design ground motions (for bedrock) in the HK region. The approximate method proposed here indicates that peak (effective) ground accelerations may reasonably be estimated to be around 10% g for 500-year earthquake events and 15-20% g for 1000-year events. However, the predicted ground motions arising from design-level earthquake events indicate large uncertainties arising from the attenuation equations. The uncertainties arise from both epistemic (event-to-event) and aleatory (site-to-site) considerations. These uncertainties represent the greatest source of errors in defining the seismic hazard for engineering design purposes. Further research is required to define the attenuation characteristics of ground motions for the CRSC, across a range of parameters including ground displacement and velocity as well as acceleration. It is further found that the Chinese earthquake building code gives a reasonably conservative estimate of seismic demand for the region, and is quite consistent with results from both probabilistic and pseudo-probabilistic seismic hazard analysis carried out herein, and by other researchers over the past 7 years. Finally, a discussion is presented of some key issues related to earthquake-resistant design and performance in Hong Kong, including the necessity to consider a range of design-level events with different MRIs when implementing acceptable structural design for earthquake effects. © 2001 Elsevier Science Ltd. All rights reserved.link_to_subscribed_fulltex