Dalam bidang oseanografi beberapa fenomena laut dapat dilihat menggunakan peta Suhu Permukaan Laut (SPL). Selain SPL, kondisi pasang surut juga penting untuk diketahui karena menggambarkan karakteristik suatu perairan. Penelitian ini bertujuan untuk mengetahui variasi SPL dan karakteristik pasang surut di perairan pulau Bali, Indonesia. Data SPL diperoleh dari National Oceanic and Atmospheric Administration (NOAA) pada 2015 – 2017 dan data pasang surut diperoleh dari Badan Informasi Geospasial (BIG) pada bulan Juni 2017 dengan interval data satu jam. Dari hasil percobaan menggunakan metode Admiralty menunjukkan bahwa tipe pasang surut di perairan pulau Bali, Indonesia tergolong Campuran dengan kecendurungan Semi Diurnal dengan bilangan Formzahl sebesar 1.01 (0.25 < F £ 1.5). Kemudian parameter elevasi Highest High Water Level (HHWL) dan Lowest Low Water Level (LLWL) yang diperoleh dari perhitungan sebesar 1.0512 dan -1.0504 meter. Selanjutnya pengolahan data SPL menunjukkan pada Juni 2015 (Musim Kemarau) nilai SPL berkisar 24.05 – 29.11 oC dengan rata-rata sebesar 27.73 oC. Kemudian pada Desember 2016 (Musim Penghujan) nilai SPL berkisar 22.96 – 28.87 oC dengan rata-rata sebesar 27.00 oC. Selanjutnya pada Februari 2017 (Musim Penghujan) nilai SPL berkisar 23.36 – 30.4 oC dengan rata-rata sebesar 27.20 oC. Sehingga dapat disimpulkan bahwa SPL di perairan Pulau Bali pada musim penghujan cenderung lebih rendah dibandingkan musim kemarau. Secara umum wilayah bagian utara pulau Bali cenderung memiliki suhu lebih tinggi dibandingkan dengan perairan bagian selatan.
GOCE gravity satellite data can be used for regional fault detection because the observation area is wide and not limited by area. In this study, GOCE satellite data is used to detect geological structures on the island of Sumatra, the results of which are used as the basis for disaster mitigation. GOCE data and SGG-UGM-2 were processed using the GOCE User Toolbox (GUT) software to produce a gravity disturbance map and a complete bouguer anomaly map. The GOCE obtained results were validated using the SGG-UGM-2 high-resolution gravity model data. The calculation results obtained that the gravity disturbance value from the GOCE data was around -140 to 200 mGal, while the value of the gravity disturbance from the SGG-UGM-2 data was around -180-300 mGal. The GOCE gravity disturbance map and the SGG-UGM-2 can detect the Subduction Trench, Mentawai Fault, and West Andaman Fault on Sumatra Island with negative values, while the Sumatran Fault Zone (SFZ) along Sumatra Island with positive values in line with the presence of mountain ranges. The results of the SGG-UGM-2 data processing for the gravity disturbance are more detailed than GOCE because the SGG-UGM-2 data degree is higher than that of GOCE. GOCE complete bouguer anomaly value is around 40-560 mGal, while the value of complete bouguer anomaly SGG-UGM-2 is around 60-560 mGal. The complete bouguer anomaly maps from GOCE and SGG-UGM-2 can detect patterns from the Subduction Trench, Mentawai Fault, and West Andaman Fault but cannot clearly detect SFZ. The complete bouguer anomaly can also detect differences between oceanic and continental crust. The GOCE and the SGG-UGM-2 complete bouguer anomaly map show almost similar patterns and the ability to detect geological structures for sub and regional Sumatra Island. In addition, GOCE data detect geological structures more clearly than GRACE data.
A Mw 6.1 earthquake on 25 February 2022, at around 8:39 a.m. local time, struck Pasaman Barat Regency, West Sumatra, Indonesia, and was felt in Singapore and Malaysia. The hypocenter of this earthquake was 12 km deep and preceded by an Mw 4.9 foreshock a few minutes earlier. The earthquakes originated on a blind fault and triggered a landslide at Mount Talamau. Herein, the slip distribution and asperities along the plane fault during the earthquake were examined by teleseismic inversion and the fault location was identified by Global Gravity Model plus (GGMPlus) satellite gravity data. The slip distribution was calculated from the source parameters (strike: 136°; dip: 70°; rake: 174°) by inversion techniques based on teleseismic data. Based on the slip distribution, the earthquake was generated by stress from the Sianok fault that spread to the north and reached the uncertain fault segment in the Talamau area. In addition, the results of the First Horizontal Derivative and Second Vertical Derivative from the GGMplus data revealed a straight Simple Bouguer Anomaly pattern, confirming the existence of the uncertain Talamau fault as part of the Great Sumatra Fault. This work shows the potential application of the combination of teleseismic and gravity observation for delineating the fault structure that caused the 2022 Mw 6.1 Pasaman earthquake, which can also be applied to other locations of similar geological backgrounds.
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