Electronic Theses and Dissertation

Gempa subduksi telah diketahui mampu menghasilkan gempa bumi yang besar dan menimbulkan kerusakan yang sangat besar serta korban jiwa. sebagian besar gempa bumi besar terjadi di bagian dangkal zona subduksi antara kedalaman 10 – 35 km, namun gempa bumi dalam di zona subduksi (kedalaman lebih dari 65 km) juga dapat menyebabkan kerusakan yang signifikan melalui fenomena guided wave. guided wave mempengaruhi penundaan waktu kedatangan gempa, meningkatkan amplitudo sinyal, dan mempertahankan sinyal frekuensi tinggi pada domain spektralnya. dengan demikian, memahami fenomena gelombang terpandu dan frekuensi dominannya sangat penting untuk disaster risk reduction (drr) serta sustainable development goals (sdgs). untuk memahami frekuensi dominan guided wave yang dihasilkan dari gempa dalam di zona subduksi, kami menggunakan sinyal gempa dalam yang direkam oleh stasiun seismik fm array. fm array terletak di taiwan utara, di mana batas lempeng konvergen, lempeng laut filipina menunjam di bawah lempeng eurasia terjadi. seismogram dianalisis menggunakan perangkat lunak seismic analysis code (sac), yang mencakup pengambilan gelombang p dan s, dan menerapkan filter narrow band pass. transformasi hilbert telah dilakukan melalui kode python, sehingga amplitudo setiap frekuensi ditentukan, dan frekuensi dominan dipilih berdasarkan amplitudo energinya. hasil penelitian menunjukkan bahwa stasiun seismik fm array telah mengamati fenomena guided wave oleh sinyal gelombang tubuh terdispersi dengan delay antara 1-1,5 detik pada pick manual dan sinyal frekuensi rendah, dibandingkan dengan stasiun lain yang tidak mengalami dispersi. selanjutnya, frekuensi dominan antara 0,5 – 5 hz ditemukan dominan pada sinyal terdispersi. frekuensi dominan juga dapat digunakan untuk memperkirakan ketebalan kerak samudera di atas lempeng subduksi. implikasi dari frekuensi dominan dapat mempengaruhi jenis bangunan, seperti frekuensi rendah yang dominan akan mempengaruhi bangunan tinggi, sedangkan sinyal frekuensi tinggi yang dominan akan mempengaruhi bangunan rendah seperti gedung 1 atau 2 lantai. kata kunci : taiwan, gempa, zona subduksi, lempeng, frekuensi dominan, gelombang terpandu, amplitudo

The subduction earthquake has been known to be able to generate large earthquakes and caused huge destruction and loss of life. Most large earthquake occurs in the shallow part of the subduction zone between 10 – 35 km deep, however, the deep earthquake in the subduction zone (greater than 65 km deep) also could contribute to significant damage through the guided wave phenomenon. The guided wave affects in delaying the earthquake arrival time, increases the signal amplitude, and preserves the high-frequency signal on its spectral domains. Thus, understanding the guided wave phenomenon and its dominant frequency is crucial for Disaster Risk Reduction (DRR) as well as Sustainable Development Goals (SDGs). To understand the dominant frequency of the guided wave resulting from the deep earthquake at the subduction zone, we use the deep earthquake signals recorded by the FM Array seismic station. The FM Array is located in northern Taiwan, where the convergent plate boundary, the Philippines Sea Plate subduct under the Eurasian Plate takes place. The seismograms were analyzed using Seismic Analysis Code (SAC) software, which includes picking P- and S-waves, and applying a narrow band passed filter. The Hilbert Transform has been performed through python codes, resulting in the amplitude of each frequency being determined, and the dominant frequency is chosen based on its energy amplitude. The results showed that the FM Array seismic stations had observed the guided wave phenomenon by dispersed body wave signals with a delay between 1-1.5 seconds on manual pick and low-frequency signal, compared to the other stations that did not experience dispersion. Furthermore, the dominant frequency between 0.5 – 5 Hz was found dominant on the dispersed signal. The dominant frequency could also use to estimate the thickness of the oceanic crust on top of the subducting plate. The implication of dominant frequency is that it can affect the type of building, such as the dominant low frequency will affect the high rise building, while, the dominant high-frequency signals will affect the low rise building such as 1 or 2 stories building. Keyword : Taiwan, Earthquakes, Subduction Zone, Plate, Dominant Frequency, Guided Wave, Amplitude