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Shear wave velocity structure beneath Bandung basin, West Java, Indonesia from ambient noise tomography
... Metode ANT digunakan untuk memperoleh tomografi kecepatan gelombang bawah permukaan pada wilayah penelitian dengan memanfaatkan data ambient noise atau noise dari lingkungan. Metode ANT telah diterapkan di Indonesia untuk mencitrakan bawah permukaan dangkal di Danau Toba, Sumatera Utara [3], Jawa Tengah [4], Cekungan Jakarta [5], Cekungan Bandung [6], struktur kerak atas di bawah Jawa Timur-Bali [7], Jawa Barat [8], dan Lombok [9]. Data yang digunakan dalam penelitian ini adalah data seismik komponen vertikal dari sensor seismometer jaringan INATEWS-BMKG. ...
... Metode ANT digunakan untuk memperoleh tomografi kecepatan gelombang bawah permukaan pada wilayah penelitian dengan memanfaatkan data ambient noise atau noise dari lingkungan. Metode ANT telah diterapkan di Indonesia untuk mencitrakan bawah permukaan dangkal di Danau Toba, Sumatera Utara [3], Jawa Tengah [4], Cekungan Jakarta [5], Cekungan Bandung [6], struktur kerak atas di bawah Jawa Timur-Bali [7], Jawa Barat [8], dan Lombok [9]. Data yang digunakan dalam penelitian ini adalah data seismik komponen vertikal dari sensor seismometer jaringan INATEWS-BMKG. ...
Pulau Sulawesi dan Nusa Tenggara Timur (NTT) merupakan wilayah yang memiliki tatanan tektonik kompleks, sehingga penting untuk menggambarkan kondisi bawah permukaan wilayah tersebut. Metode Ambient Noise Tomography (ANT) digunakan untuk memahami struktur tektonik tersebut dengan mencitrakan struktur kerak atas di bawah area penelitian ini. Pada penelitian ini, kami menggunakan data waveform komponen vertikal dari Januari 2020 hingga Mei 2021 dari 89 seismograf INATEWS- BMKG di Pulau Sulawesi dan NTT. Secara umum, tahap pertama dimulai dari pemrosesan data berfokus pada persiapan data tunggal dan korelasi silang untuk memperkiraan fungsi Green antara pasangan stasiun. Estimasi waktu tempuh kelompok gelombang Rayleigh untuk periode 2 s dan 12 s diperoleh dari waktu tunda hasil korelasi silang. Peta yang diperoleh menunjukkan variasi kecepatan gelombang Rayleigh di daerah penelitian berkisar antara 1,8 – 2,5 km/s. Teknik analisis frekuensi-waktu (Frequency-Time Analysis) digunakan untuk mendapatkan kurva dispersi untuk mengukur kecepatan kelompok antar stasiun. Kecepatan grup digunakan sebagai input dalam inversi tomografi. Proses tomografi dilakukan dengan menggunakan FMST v1.1 dimana pemodelan forward dan inverse dilakukan secara iteratif. Hasil pemodelan untuk periode 2 s menunjukkan bahwa Sulawesi Barat dan Sulawesi Utara memiliki anomali kecepatan yang lebih rendah (1,8 km/s) dibandingkan wilayah lain (2,0 – 2,3 km/s). Pada periode 12 s anomali kecepatan rendah berada di wilayah Sulawesi Utara. Anomali kecepatan rendah ini berkorespondensi dengan gunung berapi dan dataran Inter-Volcano yang berumur Kuarter di Sulawesi. Sementara untuk wilayah NTT nilai kecepatan gelombang Rayleigh berkisar antara 1,8 – 2,4 km/s.
... ANT uses surface waves, and one particularly useful characteristic of surface waves is that they are dispersive, so that different frequencies are sensitive to properties at different depths, which allows us to obtain information about how seismic velocity varies with depth in the earth (Dziewonski et al., 1969;Snieder, 2004). ANT has been applied in Indonesia to learn about the shallow subsurface image of Lake Toba in North Sumatra (Stankiewicz et al., 2010), Central Java (Zulfakriza et al., 2014), Jakarta basin (Saygin et al., 2016), Bandung basin (Pranata et al., 2019), the upper crustal structure beneath East Java-Bali (Martha et al., 2017), West Java , and the Agung-Batur Volcano complex . ...
We have successfully conducted the first ambient noise tomography on the island of Lombok, Indonesia using local waveform data observed at 20 temporary stations. Ambient noise tomography was used to delineate the seismic velocity structure in the upper crust. The waveform data were recorded from August 3rd to September 9th, 2018, using short-period and broadband sensors. There are 185 Rayleigh waves retrieved from cross-correlating the vertical components of the seismograms. We used frequency-time analysis (FTAN) to acquire the interstation group velocity from the dispersion curves. Group velocity was obtained for the period range of 1 s to 6 s. The group velocity maps were generated using the subspace inversion method and Fast Marching Method (FMM) to trace ray-paths of the surface waves through a heterogeneous medium. To extract the shear wave velocity (Vs) from the Rayleigh wave group velocity maps, we utilize the Neighborhood Algorithm (NA) method. The 2-D tomographic maps provide good resolution in the center and eastern parts of Lombok. The tomograms show prominent features with a low shear velocity that appears up to 4 km depth beneath Rinjani Volcano, Northern Lombok, and Eastern Lombok. We suggest these low velocity anomalies are associated with Quaternary volcanic products, including the Holocene pyroclastic deposits of Samalas Volcano (the ancient Rinjani Volcano) which erupted in 1257. The northeast of Rinjani Volcano is characterized by higher Vs, and we suggest this may be due to the presence of igneous intrusive rock at depth.
Noise Tomography is one of geophysical passive seismic method to utilize a coherent ambient noise who created naturally due to presence of the rotation of the earth (sea wave, gust wind, water movement that produces vibration) to detect discontinuity of wave (based on velocity measurement that correlated at multiple station) on inhomogeneity medium to determine the physical properties of rock from subsurface. In this research, we used 20 unit of Lennartz 3D-lite short period seismometer with Taurus Digitizer and record 24-72 hours on 22 days at TFQ1 Geothermal Field. Then, we process the data with several techniques to correlate recorded data on the station such as pairing technique, clustering technique and ring creation techniques on PertaGAMANT (Pertamina’s software). Result of 1D velocity model in this research can be used to determine a subsurface permeability of rock on geothermal field.
Borneo and Sulawesi are two large islands separated by the Makassar Strait that lie within the complex tectonic setting of central Indonesia. The seismic structure beneath this region is poorly understood due to the limited data availability. In this study, we present Rayleigh wave tomography results that illuminate the underlying crustal structure. Group velocity is retrieved from dispersion analysis of Rayleigh waves extracted from the ambient noise field by cross-correlating long-term recordings from 108 seismic stations over a period of 8 months. We then produce a 3-D shear wave velocity model via a two-stage process in which group velocity maps are computed across a range of periods and then sampled over a dense grid of points to produce pseudo-dispersion curves; these dispersion curves are then separately inverted for 1-D shear wave velocity (Vs), with the resultant models combined and interpolated to form a 3-D model. In this model, we observed up to ± 1.2 km/s lateral Vs heterogeneities as a function of depth. Our models illuminate a strong low shear wave velocity (Vs) anomaly at shallow depth (≤ 14 km) and a strong high Vs anomaly at depths of 20 – 30 km beneath the North Makassar Strait. We inferred the sediment basement and Moho depth from our 3-D Vs model based on iso-velocity constrained by the positive vertical gradient of the Vs models. The broad and deep sedimentary basement at ∼14 ± 2 km depth beneath the North Makassar Strait is floored by a shallow Moho at ∼22 ± 2 km depth, which is the thinnest crust in the study area. To the east of this region, our model reveals a Moho depth of ∼45 ± 2 km beneath Central Sulawesi, the thickest crust in our study area, which suggests crustal thickening since the late Oligocene. Moreover, the presence of high near surface Vs anomalies with only slight changes of velocity with increasing depth in southwest Borneo close to Schwaner Mountain (SM) confirm the existence of a crustal root beneath this region.
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