Due to recent increase in human felt tremors in Malaysia, this study aims at proposal of an appropriate setting of strong motion observation, highlighting the importance of long period ground motion. Two ways are taken to emphasize the long period ground motion (LPGM) for the strong motion observation in Malaysia that is in the deterministic way and statistical way. Recorded Sumatra event on September 29, 2009 at IPM broadband station in Malaysia were selected and in Japan, three Kik-net stations recording four events, coded as S1, S2, S3 and S4, occupied with borehole and surface sensors, with depth ranging from shallow, intermediate and very deep were selected.
In deterministic way, the product of the transfer function, namely Fourier spectra ratio, obtained from S2 event with IPM true ground motion, will produce the synthetic waveform at each ground model. Next, from the synthetic waveform deterministic estimate of acceleration (Sa) and velocity (Sv) response spectra were calculated. For the statistical way, mean Sa ratio of four events were calculated. Then the product of mean Sa ratio with the estimated bedrock motion using the attenuation relation of Yuzawa and Kudo (2006) were obtained at each ground model.
Results show small amplitude of acceleration with long duration of motions about 20 minutes. The obtained deterministic estimate of Sa and Sv shows predominant periods around 0.7 to 0.8 second and 9 seconds respectively, which can still be observed with the appearance of other peaks that seems to be controlled by the thickness of the sediments or soil layers at each ground models. Statistical estimate of Sa shows three times higher than the deterministic estimate of Sa and might be due to the regionality in the attenuation characteristic of Malaysia and Japan. However, the trend is similar and thus the results are acceptable.
Considerable attention is paid to the long duration of motion about 20 minutes and some possible ways to set up strong motion are proposed. For the necessity of assisting a structural design and for hazard assessment, the measure should start with the data recording in all of the current installed strong motion stations in Malaysia.