Sains Malaysiana 38(1):
69-76(2009)
Analyzing seismogram of the Earthquake C051099C, PNGon UGM,
PMG and CHTO Observation Stations to Understand the S and P Wave Veloocity Structure
(Analisis Seismogram Gempa Bumi C051099C, PNG di
Stesen Cerapan UGM, PMG
dan CH70
untuk Memahami Struktur Gelombang Halaju S dan P)
Bagus Jaya Santosa
Prodi Geofisika, FMIPA
Institut Teknologi Sepuluh Nopember
Jl. Arif Rahman
Hakim 1,
Surabaya
60111
Received : 18 February 2008 / Accepted : 18 March 2008
ABSTRACT
This research, compares the observed
seismogram of the PNG earthquake, C051099C with its synthetics in UGM, Wanagama, Indonesia, PMG, Port Moresby, PNG and CHTO,
Chiang May, Thailand. The synthetic seismogram is calculated using preliminary
earth model, which are the IASPEI91 and the anisotropic version of PREM. The
seismogram comparison is conducted after imposing a low pass filter whose corner
frequency is fixed at 20 mHz. We have found a real discrepancy on the travel time and waveform of some wave
phases, namely P, S and Rayleigh and Love surface waves, by seismogram
comparison in time domain. To correct the discrepancies, we need to adjust the earth structures, which include the depth of the Moho reflector, the velocity gradient of bh, and the
propagation velocity of the P and S waves. The correction has been conducted in
the earth layering system from the upper mantle down to the CMB, so that the
excellent seismogram fitting was obtained for nearly all phases of the targeted
waves. The used wave length for analysing is about
150 km. It turns out that the waveform of the body and surface waves is
sensitive to the change of velocity structure. The analysis of repetitive ScS depth phases at closer distance stations gives better
opportunity to investigate the S velocity structure near the CMB, something not
used by other seismologists.
Keywords: Crust thickness; fitting of P and S; seismogram
analysis; ScS and surface waves
ABSTRAK
Penyelidikan
ini dibandingkan seismogram yang dicerap semasa gempa bumi PNG, C051099C dengan sintetik di UGM, Wanegame,
Indonesia, PMG Port Moresby, PNG dan CHT0, Chiang May, Thailand. Seismogram sintetik dikira menggunakan model bumi awal iaitu IASPEI91 dan versi anisotropi PREM.
Perbandingan seismogram dijalankan selepas mengenakan turas lepasan rendah
dengan frekuensi ditetapkan pada 20mHz. Kami mendapati ketaksamaan dalam masa jalanan dan bentuk gelombang sebahagian fasa iaitu gelombang P, S dan Rayleigh dan Love
melalui perbandingan dalam domain masa. Untuk membetulkan ketaksamaan ini, struktur bumi telah diubah termasuklah kedalaman pembalik Mohor, cerun halaju bh dan halaju rambatan gelombang P dan S. Pembetulan telah dibuat
dalam sistem lapisan bumi dari mantel atas sehingga ke CMB, supaya pemadanan
seismogram yang baik di perolehi bagi semua fasa gelombang yang dituju. Panjang gelombang yang
digunakan ialah 150 km. Didapati bentuk gelombang bagi gelombang jasad dan
permukaan adalah sensitif terhadap perubahan dalam struktur halaju. Analisis berulang fasa kedalaman ScS pada stesen yang lebih hampir
memberikan peluang yang lebih baik untuk mengkaji struktur halaju S berhampiran
CMB, sesuatu yang belum pernah digunakan sebelum ini.
Kata kunci: Analisis seismogram;
ketebalan kerak; pemadanan P dan S; ScS dan gelombang permukaan
REFERENCES/RUJUKAN
Bagus
J.S., 1999. Moeglichkeiten und Grenzen der Modellierung vollstaendiger langperiodischer Seismogramme, Doktorarbeit, Berichte Nr. 12, Inst. fuer Geophysik, Uni. Stuttgart
Bagus
J.S., 2001, Mempelajari Model Bumi Berlapis dengan Seismogram, Majalah IPTEK, 13, No 3: 25-33.
Bulland, R. and
Chapman, C., 1983, Travel time Calculation, BSSA, 3, 1271-1302.
Dziewonski,
A.M. and Anderson, D.L., 1981. Preliminary Reference
Earth model, Phys. of the Earth and Plan. Int. 25: 297-356.
Dalkolmo, J., 1993. Synthetische Seismogramme fuer eine sphaerisch symmetrische, nichtrotierende Erde durch direkte Berechnung der Greenschen Funktion, Diplomarbeit, Inst. fuer Geophys., Uni. Stuttgart
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, Geophys. J. Int. 122: 537-550.
Gubbins,
D., 1990, Seismology and Plate Tectonics,
Cambridge University Press, Cambridge.
Kennett,
B.L.N., 1991. IASPEI 1991, Seismological
Tables, Research
School
of
Earths
Sciences,
Australian
National
University.
Keyser,
M., Ritter, J.R.R,
Jordan
,
M., 2002. 3-D shear wave velocity structure ofthe Eifel plume,
Germany
, Earth and Plan. Sci. Letters, 203: 59-82.
Souriau,
A. & Poupinet, G., 1991. A study of the outermost liquid core using differential travel times
of the SKS, SKKS and S3KS phases, Phys.
of the Earth and Plan. Int., 68. 1-2: 183-199.
Wittlinger,
G., Vergne, J., Tapponnier,
P., Farra, V., Poupinet,
G., Jiang, M., Su, H., Herquel, G. and Paul, A.,
2004. Seismic imaging of subducting lithisphere and Moho offsets beneath western
Tibet
, Earth and Plan. Sci. Letters 221: 117-130.
Wysession,
M.E., Valenzuela, R.W., Zhu, A. and Bartkö L., 1995. Investigating the base of the mantle using differential travel
times, Phys. of the Earth and Plan. Int., 92. 1-2: 67-84.
Zhao,
D, 2004. Global tomographic imaging of mantle plumes
and subducting slabs: Insight into deep Earth
dynamics, Phys. of the Earth and Plan.
Int. 146: 3-34.
|