Kesan tapak seismik merupakan salah satu kebimbangan utama dalam rekabentuk gempa bumi untuk struktur. Tapak yang lembut akan membesarkan kesan gelombang seismik di permukaan bumi. Disertasi ini membentangkan cara yang ringkas dan mudah untuk menganggar ketebalan sedimen di tapak dengan menggunakan teknik pemerhatian gegaran mikro. Pemerhatian gegaran mikro telah dijalankan di 103 tapak yang terpilih di sekitar kawasan Kuala Lumpur. Geologi Kuala Lumpur terdiri daripada Formasi Kenny Hill, batu kapur, granit dan Hawthornden Schist tetapi ketebalan sedimen yang terdiri daripada mendapan aluvium, baki lombong dan tanah baki masih tidak diketahui. Oleh itu, frekuensi tabii tanah di setiap tapak ditentukan berdasarkan kaedah Nakamura. Dapatan kajian menunjukkan frekuensi tabii tanah di Kuala Lumpur berada dalam julat 1.48 Hz hingga 5.85 Hz. Purata frekuensi tabii tanah di Kuala Lumpur ialah 3.11 Hz. Pengezonan mikro seismik berdasarkan frekuensi tabii tanah Kuala Lumpur telah dihasilkan untuk tujuan rekabentuk gempa bumi. Dalam usaha membangunkan hubungan empirikal untuk mengaitkan frekuensi tabii tanah dengan ketebalan tanah lembut, sebanyak 14 tapak yang diketahui kedalaman tanah sampai batu dasar kejuruteraan daripada laporan geoteknikal di kawasan kajian telah dirujuk. Hubungan antara ketebalan sedimen lembut (h) dan frekuensi tabii tanah (f) telah dibangunkan sebagai h = 121.16f -1.538. Berdasarkan hubungan ini, ketebalan sedimen lembut di Kuala Lumpur telah dianggarkan dan diplotkan dalam peta. Kedalaman tanah lembut di sekitar Kuala Lumpur adalah di antara 8 m hingga 66 m. Dapatan kajian daripada projek ini dapat memberikan infomasi yang berguna kepada jurutera untuk menganggar ketebalan tanah lembut di kawasan Kuala Lumpur berdasarkan ciri-ciri dinamik tanah yang diukur daripada pemerhatian gegaran mikro.
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Seismic site effect is one of the major concerns in earthquake design of structures. Soft ground tends to amplify the seismic wave in surficial geological layers. This dissertation presents a simple and convenient approach to estimate the soft sediment cover thickness at site using microtremor observation technique. A total number of 103 observation points were conducted at selected sites around Kuala Lumpur area using microtremor measuring instrument. The bedrock of Kuala Lumpur area is formed by Kenny Hill Formation, limestone, granite and the Hawthornden Schist but the thickness of soft sediment formed by alluvial deposits, mine tailings and residual soils still remains unknown. Hence, the predominant frequency of ground in each site was determined based on Nakamura method. The results show that the predominant frequency observed in Kuala Lumpur ranges from 1.48 Hz to 5.85 Hz. Kuala Lumpur has an average predominant frequency of 3.11 Hz. Seismic microzonation map based on predominant frequency for Kuala Lumpur was produced for seismic design purpose. In order to develop an empirical correlation to relate the ground predominant frequency and sediment cover thickness, a total number of 14 sites with known depth to engineering bedrock from geotechnical reports in the study area were referred. The relationship of thickness of soft sediment (h) and predominant frequency of soil (f) was established as h = 121.16f -1.538. Based on the established relationship, the thickness of soft sediment in Kuala Lumpur was determined from the result of microtremor survey and plotted in a map. The depth of the soft soil in Kuala Lumpur region ranges from 8 m to 66 m. The findings from this project provide useful information for engineers to estimate the soft sediment cover thickness in Kuala Lumpur area based on the dynamic characteristics of the ground measured from microtremor observation.
Development of seismic microzonation map and mapping of soft sediment thickness in Kuala Lumpur by using microtremor survey / Chiew Chang Chyau