SEISMOGRAM ANALYSIS OF EARTHQUAKES IN SUMATRA-JAVA AT HYB OBSERVATORY STATION

B.J. B.J. Santosa

Abstract


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.


Keywords


Seismogram analysis; Vertical anisotropy; Positive velocity anomaly

Full Text:

PDF

References


Boschi, L. and Dziewonski, A., 1999. High- and low-resolution images of the earth’s mantle: Implications of different approaches to tomographic modeling, Journal of Geophysical Research, 104, 25567 – 25594.

Dalkolmo, J., 1993. Synthetische Seismogramme für eine sphärisch symmetrische, nichtrotierend Erde durch direkte Berechnung der Greenschen Funktion. Diplomarbeit, Inst. für Geophys., Uni. Stuttgart

Dreger, D.S., 2002. Time-Domain Moment Tensor INVerse Code (TDMT_INVC), The Berkeley Seismological Laboratory (BSL), report number 8511

Dziewonski, A.M. and Anderson, D.L., 1981. Preliminary reference earth model. Phys. of the Earth and Plan. Int., 25, 297 – 356.

Engdahl, E.R., Van Der Hilst, R.D., & Buland, R.P., 1998. Global teleseismic earthquake relocation with improved travel times and procedures for depth determination, Bull. Seism. Soc. Am., 88, 722 - 743.

Friederich, W. and Dalkolmo, J., 1995. Complete synthetic seismograms for a spherically symmetric earth by a numerical computation of the green’s function in the frequency domain. Geophysical Journal International, 122, 537 - 550.

Garnero, E., 2000. Heterogeneity of the lowermost mantle. Annu. Rev. Earth Planet. Sci., 28, 509–537.

Gomer, B.M. and Okal, E.A., 2003. Multiple-ScS probing of the Ontong-Java Plateau, Physics of the Earth and Planet Interiors, 138, pp. 317 – 331.

Grand, S., van der Hilst, R. & Widiyantoro, S., 1997. Global seismic tomography: a snapshot of convection in the Earth. GSA Today, 7, 1–7.

Hall, R., 2002. Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer based reconstructions, model and animations, Journal of Asian Earth Sciences, 20, 353 – 431

Nettles, M. and Dziewonski, A.M., 2008. Radially anisotropic shear velocity structure of the upper mantle globally and beneath North America, Journal of Geophysical Research, 113, B02303, doi:10.1029/2006JB004819

Panning, M. and Romanowicz, B., 2008. A three-dimensional radially anisotropic model of shear velocity in the whole mantle. Geophysical Journal International, 167, pp. 361 - 379.

Replumaz, A, Kárason, H, van der Hilst, R. D., Besse, J. & Tapponnier, P., 2004. 4-D evolution of SE Asia’s mantle from geological reconstructions and seismic tomography, Earth and Planetary Science Letters, 221, 103 – 115

Singh, D.D., 1999. Surface wave tomography studies beneath the Indian subcontinent, Geodynamic, 28, pp. 291 – 301.

Takeuchi, N., 2007. Whole mantle SH velocity model constrained by waveform inversion based on three-dimensional Born kernels, Geophysical Journal International, 169, Number 3, June 2007, pp. 1153 – 1163.

van der Hilst, R., Widiyantoro, S. & Engdahl, E., 1997. Evidence for deep mantle circulation from global tomography. Nature, 386, 578–584.

Vasco, D., Johnson, L. & Pulliam, R., 1995. Lateral variations in mantle velocity structure and discontinuities determined from P, PP, S, SS, and SS-ScS travel time residuals. J. Geophys. Res., 100, 24037–24059.

Wysession, M., Lay T. & Revenaugh J., 1998. The D” discontinuity and its implications. In: Gurnis, M., Buffett, B., Knittle, K., Wysession, M. (Eds.), The Core–Mantle Boundary. Am. Geophy. Union, pp. 273–297.

Zhao, D., 2001. Seismic structure and origin of hotspots and mantle plumes, Earth and Planetary Science Letter, 192, 251–265.

Zhao, D., 2004. Global tomographic images of mantle plumes and subducting slabs: insight into deep Earth dynamics, Physics of the Earth and Planetary Interiors, 146, 3–34

Zhou, H., 1996. A high-resolution P wave model for the top 1200 km of the mantle. Journal of Geophysical Research, 101, 27791 – 27810.




DOI: https://doi.org/10.15294/jpfi.v8i2.2160

Refbacks

  • There are currently no refbacks.




Creative Commons License
Jurnal Pendidikan Fisika Indonesia is licensed under a Creative Commons Attribution 4.0 International Licensep-ISSN 1693-1246 e-ISSN 2355-3812