IDENTIFIKASI DINAMIKA MAGMA BERDASARKAN ANALISIS TREMOR VULKANIK DI GUNUNGAPI SLAMET JAWA TENGAH; IDENTIFICATION OF MAGMA DINAMIC BASED ON VOLCANIC TREMOR ANALYSIS AT SLAMET VOLCANO CENTRAL JAVA

LUMBANRAJA, WANRI, N

2016 | Disertasi | FMIPA

During the active phase in 2014 five seismometers installed around Slamet volcano begun recording tremor signal in mid-July. The existence of this tremor were followed by eruptions of ash and lava burst occurred a few weeks later until eruptions on the earlier to mid-September 2014. In addition to the data tremors, all of volcanic seismic activity are also stored in the form of RSAM. Analysis of volcanic tremor signal and RSAM has been done to study the magma dynamics and its relations with the eruption. Spectral analysis was done by applying some standard methods, including Maximum Entropy Methods, Fourier Transform, Periodogram and Coherence. In addition to spectrum analysis, polarization analysis was also applied to determine the seismic waves’s characteristics. The range of the spectrum contained by the signal relatively narrow, lies between 1 Hz to 4 Hz, where the dominant power spectral peak lies in frekuesi average of 2.0 Hz and 3.1 Hz. There is a relation between the pattern of the power spectrum with the leaking of magma to the surface, that is, the eruption occurred initiated by the weakening or loss of power frequency of 3.1 Hz. Particle motion analysis showed the presence of the Rayleigh wave which propagate to the north direction. The existence of Raylaigh wave confirm that the source of tremor is relatively shallow beneath the summit, relative to the 3 components seismometer. In addition, the SH wave was also observed in the direction tangential to the summit. Azimuth and angle of incidence analysis also shows a change in the pattern. When approaching eruption phase, azimuth angle which initially concentrated in the direction of 30 degrees tends to spread toward 0 degrees, the angle of incidence tends to spread from the direction of 75 degrees to 90 degrees and its dominant constant at 75 degrees. These results lead to the conclusion that the dynamics of magma ascent to the summit indicate the changes of signal pattern.

Kata Kunci : Tremor, M.Slamet, RSAM, Magma Dinamic, Maximum Entropy Method, Polarization, Particle Motion.