Electronic Theses and Dissertation

Metode tomografi seismik gelombang badan (gelombang P dan S) telah diaplikasikan untuk kajian struktur kerak bumi Namibia. Namibia merupakan salah satu negara bagian Afrika Selatan yang cukup aktif mengalami aktivitas seismik yang terjadi karena adanya proses rift-tectonic dan aktivitas patahan aktif. Eksperimen seismik pasif di Namibia menggunakan 29 stasiun darat jaringan seismik WALPASS dilakukan selama 3 tahun, antara November 2010 hingga November 2012. Tujuan dari kajian ini adalah untuk menyelidiki pola patahan aktif dan struktur kerak bumi di Namibia berdasarkan sebaran gempa bumi dan struktur Vp & Vp/Vs. Lokalisasi awal gempa bumi dihasilkan dari penentuan waktu tiba gelombang P dan S menggunakan HYPO71 yang tersedia di dalam Xquake. Hasil lokalisasi awal diperoleh sebanyak 1.335 event gempa bumi dengan 9 cluster gempa bumi awal. Sebanyak 1.114 event gempa bumi dengan kriteria nilai RMS residual ≤ 1 s dilakukan relokasi gempa bumi dan inversi penentuan model kecepatan 1-D optimum menggunakan metode coupled velocity hypocenter di dalam VELEST. Hasil relokasi gempa bumi diperoleh RMS residual 0,508 s. Hasil model kecepatan 1-D optimum kemudian akan dilakukan inversi tomografi seismik 3-D secara simultan menggunakan kode program SIMUL2000. Hasil inversi tomografi seismik berupa sebaran seismisitas, struktur Vp dan Vp/Vs mengungkapkan adanya pola patahan dan litologi stuktur kerak Namibia. Sebanyak 9 patahan aktif Namibia berhasil diidentifikasikan dengan 5 patahan memiliki orientasi barat laut – tenggara dan 4 patahan memiliki orientasi timur laut – barat daya. Struktur Vp dan Vp/Vs dicitrakan hingga kedalaman 60 km dengan nilai Vp diperoleh antara 4 - 8 km/s, sedangkan nilai Vp/Vs diperoleh antara 1,68 – 1,78. Berdasarkan nilai Vp dan Vp/Vs tersebut, litologi kerak bumi Namibia didominasi oleh batuan kering berisi gas dengan karakteristik Vp/Vs rendah (

The seismic tomographic method of body wave (P and S waves) has been applied to the study of Namibian earth crust structures. Namibia is one of the relatively active South African states experiencing seismic activity caused by tectonic rifting and active fault activities. A passive seismic experiment with 29 stations was setup for 3 years from November 2010 to November 2012. The objective of this research is to investigate the active fault and structures of the earth’s crust in Namibia based on the Vp and Vp/Vs structures and distribution of seismicity. The initial earthquakes localization was determined of the first-break arrival time of P and S waves using HYPO71 provided in Xquake. The number of earthquake localization results obtained as many as 1.335 earthquakes events with 9 clusters of seismicity. There were 1.114 earthquakes events with the criteria of residual RMS value ≤ 1 s were relocated and inversion of the optimum 1-D velocity model by using coupled velocity hypocenter method in VELEST. The results of the earthquake relocation obtained RMS residual 0,0505 s and the optimum 1-D velocity model will be performed simultaneous inversion for the 3-D tomographic velocity structure using the program code SIMUL2000. The inversion of seismic tomographic is the distribution of seismicity, Vp and Vp/Vs structure reveals fault patterns and lithology of Namibia’s crustal structure. A total of 9 active faults were identified which is delineating 5 NW-SE active faults and 4 NE-SW active faults orientation. The Vp and Vp/Vs structure is well resolved to a depth of 60 km with Vp values are obtained from 4 – 8 km/s and Vp/Vs values are obtained from 1,68 – 1,78. Based on the Vp and Vp/Vs values, the lithology of Namibia earth crustal is dominated by gas-saturated rocks characterized by low Vp/Vs (