ANALISIS KARAKTERISTIK SEISMIK PADA EVENT HEMBUSAN GUNUNGAPI MERAPI YOGYAKARTA PERIODE JULI 2012

SITI NURMABRUROH, Dr. Ing Ari Setiawan

2014 | Tesis | S2 Ilmu Fisika

Event hembusan gunung Merapi yang terjadi pada tanggal 15 Juli 2012 terekam di stasiun Pasar Bubar, Klatakan, Deles, Plawangan, dan Pusung London. Event hembusan ditandai dengan keluarnya gas dan material halus dari dalam kawah yang muncul ke permukaan. Sampai saat ini event hembusan belum diketahui karakteristiknya, sehingga dilakukan kajian komprehensif terkait seismisitasnya. Pada penelitian ini event hembusan dianalisis dengan menggunakan: time frequency analysis, korelasi, dan particle motion. Time frequency analysis dilakukan di stasiun Pasar Bubar, Klatakan, Deles, Plawangan, dan Pusung London. Korelasi sinyal dilakukan antara stasiun Pasar bubar dengan stasiun Klatakan, Deles, Plawangan, Pusung London. Particle motion dilakukan di stasiun sesmik tiga komponen yakni di stasiun Klatakan dan Pasar Bubar untuk menentukan back azimuth (𝛼), incidence angle (𝑖 ), dan arah dominan event hembusan. Hasil analisis frekuensi menunjukkan bahwa dari masing-masing seismogram yang terekam di stasiun Pasar Bubar, Klatakan, Deles, Plawangan, dan Pusung london kandungan frekuensinya antara 2-12 Hz. Hasil analisis korelasi berdasarkan waktu kejadian dari event hembusan yang terekam diseluruh stasiun menunjukkan bahwa korelasinya kecil 𝜑 = 0,32-0,55. Nilai korelasi yang kecil tersebut diasosiasikan sebagai pergeseran fase dari arah penjalaran gelombang antar stasiun. Analisis particle motion di stasiun Klatakan menunjukkan nilai back azimuth (∝) 141° dan incidence angle (i) 227°, sedangkan di stasiun Pasar Bubar nilai back azimuth (∝) 154°, episenter terletak di 7°32′54′′ LS dan 110°28′29′′ BT dan hiposenter pada kedalaman 5982 m dari stasiun klatakan. Arah dominan event hembusan saat terjadi crack searah azimuth, yakni radial terhadap bidang datar.

Merapi volcano degassing event occurred in 15 July 2012 was recorded by stations located in Pasar Bubar, Klatakan, Deles, Plawangan, and Pusung London. Events marked with gusts of gas and fine material from the crater surface. During the time, the characteristic of the degassing event have been unknown so a comprehensive study of its seismicity is needed. In this research, degassing event was analyzed using time frequency analysis, crosscorrelation, and particle motion. The time frequency was analyzed for stations in Pasar Bubar, Klatakan, Deles, Plawangan, and Pusung London. Signal correlation had been calculated between station Pasar Bubar with station Klatakan, Deles, Plawangan, and Pusung London. Particle motion analysis was performed in three component seismic station, which are Klatakan and Pasar Bubar to determine the back azimuth (α), incidence angle (i) and the dominant direction of gusts event. The results of the analysis showed that the range frequency of each seismogram recorded at Pasar Bubar, Klatakan, Deles, Plawangan, and Pusung london station is between 2-12 Hz. The correlation analysis result of degassing events recorded by all stations shows that the small correlation (φ = 0.32 to 0.55) was associated with phase shift of wave propagation’s direction between stations. Analysis of particle motion show that in Klatakan station, the value of back azimuth (α) is 141 °and the incidence angle (i) is 227 °. Meanwhile, back azimuth value (α) in the Pasar Bubar station is 154 °. The epicenter is located at 7 ° 32'54'' S and 110 ° 28'29'' E and the hypocenter is at a depth of 5982 m from the station Klatakan. The dominant direction of degassing event when the cracks occured was in the direction of the azimuth of horizontal plane

Kata Kunci : Event hembusan Merapi 2012, analisis time frequency, korelasi, particle motion