B.J. B.J. Santosa


Dalam penelitian ini struktur bumi di bawah lempeng Lautan Hindia Timur Laut dikaji melalui analisis seismogram atas seismogram gempa-gempa bumi yang terjadi di Sumatra dan direkam di stasiun observasi HYB, India. Analisis seismogram dilaksanakan dalam domain waktu dan ketiga komponen-komponen Kartesian secara simultan. Perbandingan seismogram menunjukkan bahwa model bumi global PREM memberikan seismogram sintetik yang menyimpang dari seismogram terukur dan waktu tiba gelombang S yang lebih lambat dibandingkan waktu tiba terukur. Untuk mencapai pencocokan seismogram, gradient βh di upper mantle diubah dari positif menjadi negative, sebagaimana dinyatakan dalam model bumi PREMAN, dan koreksi kecepatan positif ditambahkan pada koefisien-koefisien kecepatan orde nol pada struktur kecepatan S dalam semua lapisan mantel bumi. Pengepasan yang bagus dicapai pada gelombang ruang S, gelombang permukaan Love dan Rayleigh, begitu juga dengan gelombang terpantul inti bumi ScS dan ScS2.

In this research, the earth structure beneath North East Indian Ocean plates is investigated using waveform analysis of Sumatra’s earthquakes recorded in HYB station. Seismogram analysis was conducted in the time domain and three Cartesians components simultaneously. The seismogram comparison shows that the global earth mantle of PREM provides deviating synthetic seismogram and has later arrival times than those from the measurement. To achieve the seismogram fitting, the gradient βh in the upper mantle layers was altered to positive from its negative slope as stated in the PREM model, and positive corrections are added to the zero order of polynomials coefficients of S velocity structure in all earth mantle layers. The excellent fitting, as well as travel time and waveform, were achieved on the S wave, Love and Rayleigh surface waves, as well as the ScS and ScS2 core reflected waves.


Seismogram analysis; Vertical anisotropy; Positive velocity anomaly

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