PREKURSOR GEMPA BUMI PADANG 2009 BERBASIS HASIL ANALISIS POLARISASI POWER RASIO DAN FUNGSI TRANSFER STASIUN TUNGGAL

Ahadi Suaidi, Puspito N.T, Saroso S, Ibrahim G, Siswoyo Siswoyo, Suhariyadi Suhariyadi

Abstract


Gempa bumi Padang 2009 (Mw=7,6) adalah salah satu gempa bumi kuat di Sumatera setelah gempa bumi kuat Aceh 2004 dan Nias 2005. Gempa tersebut sangat menarik untuk diteliti karena memiliki magnitudo gempa (Mw = ~7), dengan jarak hyposenter gempa bumi yaitu RPadang = 140 km (< 200 km). Azimuth episenter stasiun geomagnet Kototabang (KTB) memiliki arah 2050 UT (Utara-Timur) terhadap posisi episenter. Analisis emisi ULF (Ultra Low Frequency, f < 0,1 Hz) yang terekam pada magnetogram, telah dilakukan dengan menganalisis spektrum frekuensi pada saat sebelum – saat kejadian (pre-seismic) guna mengetahui seberapa besar jangkauan frekuensi yang muncul akibat aktifitas seismogenik. Dalam penelitian ini metode polarisasi power rasio telah digunakan untuk mendapatkan waktu mula (onset time) untuk prekursor gempa. Selanjutnya, dengan Fungsi Transfer Stasiun Tunggal (Transfer Function Single Station) azimuth dari anomali konduktivitas akibat aktivitas seismogenik dapat diketahui. Hasilnya adalah ditemukan waktu mula (Onset Time) dan azimuth dari anomali konduktivitas dimana anomali emisi ULF diketahui selama 26 hari sebelum kejadian dengan arah azimuth dari perhitungan fungsi tranfer adalah 2050. Dengan demikian informasi anomali emisi ULF dengan menggunakan data geomagnet dapat menentukan prekursor gempa bumi dengan jangka pendek (short -time).

 Kata Kunci: Gempa Sumatera, Emisi ULF, Prekursor Gempa Bumi, Jangka Pendek.

 

 ABSTRACT

 The 2009 Mw=7.6 Padang earthquake is among strong earthquakes in Sumatra after the Aceh 2004 and Nias 2005 strong earthquakes. Research on this earthquake is very interesting because it has a high magnitude (Mw=~ 7), with distance to hypocenter was RPadang = 140 km or (< 200 km). Azimuth epicenter from Kototabang Geomagnetic Station (KTB) has directions to 2050 NE to the position of the epicenter. Analysis of Ultra Low Frequency (ULF) emissions ( f < 0.1 Hz), that was recorded on the magnetogram, was analyzed by using the frequency spectrum at the time prior to the event (pre-seismic) to determine how large was the range of frequencies that arise from the seismogenic activity. Furthermore, by using polarization power ratio method, the first time (onset time) for earthquake precursors was obtained. The azimuth of anomalous conductivity due seismogenic activity can be known by using a Transfer Function Single Station. The result shows that the Onset Time and azimuth were found from which the conductivity anomaly known anomaly ULF emissions during the 26 days prior to the event with the azimuth direction of the transfer function calculation is 2050. Thus the anomalous information of ULF emissions with geomagnetic data can be used to determine earthquake precursors in relatively short-time.

 

 Keywords: Sumatra Earthquake, ULF emission, Earthquake Precursor, And Short Term.


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