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tunnel in the biggest island of the Dangan Island was used to detect the seismic waves generated from the
explosive ignited from the seabed. The geological structures near Dangan Island area were obtained and
are illustrated in Fig. 7 (modified from Lai and Langford, 1996).
Littoral Fault Zone
^- -"* -*.'; ; -X' Dangan isiS
-. ,;x^>^-;- x
v;-'vin-^:;C;^-
' ' "0 ^ ** 40
Figure 8. A cross-section cutting through Dangan Island area showing a vertical drop of the rock head
of up to 3 km across the fault The vertical drop is filled with Quaternary deposit and forming a tensile
rift zone
The Dangan Island and Hong Kong area shows a very distinct uplift of the seabed basin through a tensile
normal fault system (see Fig. 8). The geological setting of such vertical drop of the rock head level is
similar to those observed in Shantou and Qiongshan, at where large earthquakes of magnitude of 7.5 has
been generated. Therefore, it is believed that the maximum credible earthquake magnitude at Dangan
Island area may be up to 7.5. Indeed, the China Seismological Bureau did assign such a value for the
Dangan Island seismic source during the probabilistic earthquake hazard analysis. Thus, Hong Kong may
some days subject to near field large earthquake of magnitude up to 7.5. Therefore, there is a genuine
need to incorporate seismic provisions in the building regulation.
SEISMIC PERJFORMANCE OF TALL BUILDINGS IN HONG KONG
In Hong Kong, over 70% of the land of 1,000 square km are hilly and thus most buildings constructed in
Hong Kong are high-rise in order to fully utilize the land to accommodate 7.8 millions people in such a
tiny place. As shown in Fig. l(b), tall buildings are everywhere on the Hong Kong Island. Following the
^allocation of the airport to Lantau Island in 1998, new buildings on Kowloon Peninsula are also
expected to be high-rise. Figure 9 shows the aerial photographs for both the new and old airport.
In fact, a lot of tall buildings are being built and planned in Hong Kong. For example, the "Two
International Finance Center" at the Airport Railway Station at Central is near completion. It will be the