Perbandingan Seismik Interferometri Cross Correlation Dan Cross Coherence Pada Data Seismik Pasif Untuk Perhitungan Kecepatan Gelombang P

Terakahfi, Almarsa Iman (2020) Perbandingan Seismik Interferometri Cross Correlation Dan Cross Coherence Pada Data Seismik Pasif Untuk Perhitungan Kecepatan Gelombang P. Undergraduate thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Akuisisi data seismik dibedakan menjadi dua variasi berdasarkan sumbernya
yaitu seismik aktif dan seismik pasif. Seismik pasif menggunakan sumber dari
ambient noise (sumber yang tidak diketahui letak pastinya) yang kemudian
direkam untuk mengkarakterisasi batuan dibawah permukaan tanah. Rekaman
seismik pasif tersebut diberlakukan proses seismik interferometri untuk
mendapatkan virtual source pada masing masing receiver terhadap receiver
lainnya. Dalam pembuatannya, terdapat beberapa metode yang dapat dipakai,
diantaranya adalah cross correlation dan cross coherence. Pada penelitian ini
dibuat perbandingan proses pembuatan dan hasil virtual source antara cross
correlation dan cross coherence. Akuisisi data dilakukan pada 8 titik stasiun di
sekitar Surabaya. Data hasil akuisisi kemudian dilakukan pre-processing yang
meliputi linear detrending, polynomial detrending, normalisasi rata – rata,
normalisasi amplitudo, EMD filter, dan bandpass filter. Data yang telah
dikondisikan lalu dilakukan perhitungan cross correlation dan cross coherence
untuk membuat virtual source. Virtual source lalu dilakukan stacking dengan
hari pengukuran lainnya. Hasil stacking lalu dilakukan picking pada peak
amplitudo per trace untuk mendapatkan nilai waktu tempuh antar stasiun,
kemudian dibuat permodelan cepat rambat gelombang dari nilai waktu tempuh
tersebut dengan refraction tomography. Hasil dari kedua metode pembuatan
virtual source memiliki beberapa perbedaan. Cross correlation menghasilkan
noise yang lebih rendah, sedangkan cross coherence memiliki bandwidth yang
lebih lebar (0.02 – 0.3 Hz) sehingga menghasilkan noise yang lebih tinggi dan
memiliki peak amplitudo yang lebih tinggi (0.7). Hasil dari refraksi tomografi
menghasilkan 3 rentang Vp, 300 – 400 m/s, 400 – 600 m/s, dan +880 m/s.
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Seismic data acquisition is divided into two variations based on the source,
namely active seismic and passive seismic. Seismic data is useful for knowing
subsurface characters with fairly high accuracy. Passive seismic uses a source
of ambient noise (a source whose exact location is unknown) which is then
recorded to characterize subsurface rocks. Passive seismic recording is
implemented by the interferometry seismic process to obtain a virtual source on
each receiver against the other receivers. To obtain the virtual source, there are
several methods that can be used, including cross correlation and cross
coherence. In this study a comparison is made between the process and the
results of virtual sources with cross correlation and cross coherence methods.
Data acquisition was carried out at 8 station points around Surabaya. Data
acquisition results are pre-processed which includes linear detrending,
polynomial detrending, mean normalization, amplitude normalization, EMD
filter, and bandpass filter. Virtual source creation then conducted with the cross
correlation and cross coherence method with the pre-processed data as the basis.
The virtual source then stacked with other measurement in another days. The
results of the stacking are then picked at the peak amplitude per trace to get the
value of travel time between stations, then velocity modeling of the travel time is
conducted using refraction tomography. The results of the two virtual source
creation methods have several differences. Cross correlation results is lower in
noise, whereas cross coherence has wider bandwidth (0.02 – 0.3 Hz) resulting
in higher noise and have higher peak amplitude (0.7). Refraction tomography
result indicates 3 range of Vp, 300 – 400 m/s, 400 – 600 m/s, and +880 m/s.

Item Type:	Thesis (Undergraduate)
Uncontrolled Keywords:	seismik interferometri, cross – correlation, cross coherence, seismik pasif. seismic interferometry, cross correlation, cross coherence, passive seismic.
Subjects:	Q Science > QE Geology > QE538.5 Seismic waves. Elastic waves Q Science > QE Geology > QE538.8 Earthquakes. Seismology Q Science > QE Geology > QE539.2 Seismic traveltime inversion Q Science > QE Geology > QE539.2.S4 Seismic models
Divisions:	Faculty of Civil Engineering and Planning > Geophysics Engineering > 33201-(S1) Undergraduate Thesis
Depositing User:	Almarsa Iman Terakahfi
Date Deposited:	24 Aug 2020 03:58
Last Modified:	24 Aug 2020 03:58
URI:	http://repository.its.ac.id/id/eprint/78820

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