The role of near-field ground motion on seismic risk assessment in large urban areas

41/2018

The role of near-field ground motion on seismic risk assessment in large urban areas

Tuesday 24th July 2018

Mazzieri, I.; Melas, L.; Smerzini, C.; Stupazzini, M.

During the last ten years a long series of events like Wenchuan (2008, China), l’Aquila (Italy, 2009), Christchurch (New Zealand, 2010-2011), Emilia-Romagna (Italy, 2012), Meinong (Taiwan, 2016), Kumamoto (Japan, 2016) and Norcia (Italy, 2016) once more proved that the near-field of an earthquake poses a serious threat and even buildings considered earthquake-resistant might be severely affected. As a matter of fact, during the so-called “Christchurch sequence” around 70% of the central business district's (CBD) buildings turned out to be severely damaged and required to be demolished, in spite of the state-of-the-art New Zealand seismic building code and the stringent adoption and enforcement of this latter. In this study we examine a large and representative set of numerical scenarios generated by means of physics-based simulations (PBS), in order to constrain the ground motion at short distances (within few kilometers range) by taking into account the rupture process, the seismic wave propagation and three-dimensional (3D) complex configurations. The experience gathered in the past years regarding 3D modelling of seismic wave propagation in complex alluvial basin (Guidotti et al., 2011; Smerzini and Villani, 2012) allowed us to enhance the choice of simulated scenarios in order to exhaustively explore the variability of ground motion and overcoming certain deficiency of the GMPEs and especially the insufficient number of records located close to the causative faults. All PBS presented in this study are carried out through the spectral element code SPEED (http://speed.mox.polimi.it). The large metropolitan area of Beijing (China) is considered because of the (i) proximity with a well-known mapped fault system capable to trigger a severe earthquake, a (ii) relatively good description of the geotechnical characterization of the soil and a (iii) reliable reconstruction of the deep alluvial structure. Focusing on the class of high-rise buildings and taking into account on one hand suitable fragility curves and on the other hand the aforementioned PBSs, seismic damage scenarios in the Beijing area will be produced and the variability of different damage states, as induced by a wide set of fault rupture scenarios with magnitude in the range 6.5-7.3, will be explored.

This report, or a modified version of it, has been also submitted to, or published on
Proceedings of the 16th European Conference on Earthquake Engineering (16ECEE), 2018