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Hybrid Simulations of Ground Motions from Local Earthquakes Affecting Hong Kong

¹ Kusnowidjaja Megawati
Nanyang Technological University
School of Civil and Environmental Engineering
Block N1, 50 Nanyang Avenue
Singapore 639798
kusno{at}ntu.edu.sg

Hong Kong is located in a continental intraplate region within southeastern China. Historical records indicate that Hong Kong has been affected by both moderate local earthquakes and major distant ones, but recent probabilistic seismic hazard analyses (PSHA) showed that the seismic hazard in Hong Kong was mainly dominated by strong and major earthquakes at distances between 90 and 400 km from the city. Further investigation on the result of the PSHA reveals that the conventional Gutenberg–Richter seismicity model used in the PSHA may have underestimated the probability of occurrence of local, large-magnitude earthquakes. The fact that the Dangan Island fault, which has generated a moderate earthquake in 1874, lies only 30 km southeast of Hong Kong, warrants a thorough investigation on the likely ground-motion intensities that may be produced by local earthquakes in the future. Although the seismogenic potential of the Dangan Island fault has not been assessed definitely, it could perhaps generate an M_max 7 earthquake. A series of ground-motion simulations are carried out using a hybrid kinematic-stochastic model to estimate the peak ground accelerations (PGAs), peak ground velocities (PGVs), and response spectral accelerations (RSAs) at eight representative locations within Hong Kong. The capability of the simulation model and the appropriateness of the key parameters used in the simulations are confirmed by simulating the ground motions recorded in Hong Kong during a recent microearthquake on the Dangan Island fault. The results of the simulations are used to derive a set of attenuation relationships for PGA, PGV, and RSA that will be essential for future probabilistic and deterministic seismic-hazard analyses. Using the spectral attenuation relationship derived, it is revealed that strong earthquakes with M_w 6.0–6.5 along the Dangan Island fault, rather than major distant earthquakes (M_w 7.3, R = 340 km), would dominate the seismic hazard in Hong Kong for natural periods longer 1 sec, which correspond to the natural periods of most buildings in Hong Kong. It is therefore timely for the authority to initiate a series of geological investigations to determine the slip rate of the fault system more precisely to access the actual seismogenic potential of the Dangan Island fault.