Inversi Tomografi Crosshole Seismic Near Surface Menggunakan Metode Pseudoinverse dan Least Square QR (LSQR)

Erdyanti, Rinta Bi Tari (2019) Inversi Tomografi Crosshole Seismic Near Surface Menggunakan Metode Pseudoinverse dan Least Square QR (LSQR). Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Identifikasi low velocity zone dapat dilakukan dengan metode crosshole seismic. Namun permasalahan yang dihadapi adalah ray path cenderung melalui high velocity, sehingga ray path yang melalui low velocity zone pun lebih sedikit. Akibatnya, model hasil inversi pada low velocity zone ini kurang tergambarkan dengan baik. Proses inversi ini pun dipengaruhi oleh penentuan model awal serta metode inversi yang digunakan. Penelitian ini membandingkan efisiensi metode inversi pseudoinverse dan Least Square QR (LSQR) pada model batugamping yang terkarstifikasi. Tiga jenis model awal – gradasi ke bawah, homogen, dan kotak (mirip dengan model sebenarnya, namun bentuknya dibuat blocky) – diuji dan didapatkan hasil bahwa model hasil inversi paling baik ketika model awal dibuat mendekati model sebenarnya (secara bentuk dan nilai velocity). Kemudian, metode inversi yang paling efisien dari dua metode inversi yang digunakan adalah metode LSQR. Hal ini didasarkan pada kemampuan inversi metode lsqr dapat mencapai konvergensi lebih cepat ketika menggunakan model awal yang tidak mirip dengan model sebenarnya (secara bentuk dan velocity), walaupun hasil inversinya mirip dengan hasil inversi metode pinv. Metode lsqr juga dapat menggambarkan model lebih baik ketika model awal dibuat mirip dengan model sebenarnya.
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Identification of low speed zones can be done using the seismic crosshole method. But the important thing is that the ray path is having a tendency to go through higher velocity medium, so that the ray path through the low velocity zone is even less. This is causing the inversion model at the low velocity zone can not be defined properly. It is necessary to determine the initial model carefully and using the optimum inversion method for each of these initial models. This study compares the efficiency of the pseudoinverse and Least Square QR (LSQR) inversion methods on a karstified limestone model. Three types of initial models - down gradations, homogeneous, and boxes (similar to the actual model, but the shape is made blocky) – was tested. This study shows that the model of inversion is the best model of initial compilation made new models (by shape and velocity) – boxes initial model results best inversion model. Theremore, the most efficient inversion method of the two inversion methods used is the LSQR method. This is based on the inversion ability of the LSQR method to achieve convergence faster using an initial model that is not similar to the actual model, but the inversion results are similar to the results of the inverse invocation of the pinv method. The lsqr method can also define a better model when using boxes initial model.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	crosshole seismic, inversi tomografi, LSQR, pseudoinverse, low velocity zone
Subjects:	Q Science > Q Science (General) > Q180.55.M38 Mathematical models Q Science > QA Mathematics > QA184 Algebra, Linear Q Science > QA Mathematics > QA353.K47 Kernel functions (analysis) Q Science > QA Mathematics > QA76.758 Software engineering Q Science > QA Mathematics > QA9.58 Algorithms Q Science > QE Geology > QE538.5 Seismic tomography; Seismic waves. Elastic waves
Divisions:	Faculty of Civil Engineering and Planning > Geophysics Engineering > 33201-(S1) Undergraduate Thesis
Depositing User:	Erdyanti Rinta Bi Tari
Date Deposited:	23 Jul 2026 01:31
Last Modified:	23 Jul 2026 01:31
URI:	http://repository.its.ac.id/id/eprint/65074

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