Mechanism of High Frequency Shallow Earthquake Source in Mount Soputan, North Sulawesi

DOI: 10.17014/ijog.v6i3.122Moment tensor analysis had been conducted to understand the source mechanism of earthquakes in Soputan Volcano during October - November 2010 period. The record shows shallow earthquakes with frequency about 5 - 9 Hz. Polarity distribution of P-wave first onset indicates that the recorded earthquakes are predominated by earthquakes where almost at all stations have the same direction of P-wave first motions, and earthquakes with upward first motions.In this article, the source mechanism is described as the second derivative of moment tensor, approached with first motion amplitude inversion of P-wave at some seismic stations. The result of moment tensor decomposition are predominated by earthquakes with big percentage in ISO and CLVD component. Focal mechanism shows that the recorded earthquakes have the same strike in northeast-southwest direction with dip about 400 - 600. The sources of the high frequency shallow earthquakes are in the form of tensile-shear cracks or a combination between crack and tensile faulting

Mekanisme Gempa Vulkanik Gunung Talang Pasca Gempa Tektonik Mentawai Tahun 2007-2009, Sumatra Barat

DOI: 10.17014/ijog.v5i3.104The Mentawai tectonic earthquake (magnitude 6.8 on the Richter Scale) on April 10, 2005 is assumed to trigger Talang volcanic activity that caused an eruption on April 12, 2005. Information on the source mechanism of volcanic earthquakes after the tectonic earthquake is expected to answer question of “Do tectonic earthquakes around the Talang Volcano trigger its volcanic activities?” Epicenter distribution of the volcanic earthquakes between 2007 and 2009 shows a southeast – northwest pattern with dextral strike-slip fault and normal fault mechanisms. The data show that earthquake activities at the Talang Volcano were dominated by local structure movements influenced by regional tectonic movements. Between 2007 and 2009, there were three process stages related to magnitude 6 or larger tectonic earthquakes around the Talang Volcano. First stage was a period before August 16, 2009. In this stage, volcanic fluids rose to the shallower chamber beneath the Talang Volcano. Second stage was a compressional stage and formation of a reverse fault influenced by Mentawai tectonic earthquake on August 16, 2009 and activation of a fault that intersects the Volcano. The third stage was a compresional stage and formation of a reverse fault influenced by Padang tectonic earthquake on September 30, 2009. In this stage, area fracturing was intensified, thereby the fracturing became more intensive. As the result, the accumulated volume and pressure of several tectonic earthquakes were released that caused an increase of eruption column soon after the tectonic earthquake

Mekanisme Sumber Gempa Dangkal Frekuensi Tinggi di Gunung Soputan, Sulawesi Utara

Analisis tensor momen telah dilakukan untuk mengetahui mekanisme sumber gempa di Gunung Soputanpada Oktober - November 2010. Gempa yang terekam merupakan gempa-gempa dangkal dengan frekuensisekitar 5 - 9 Hz. Distribusi polaritas onset awal gelombang P menunjukkan bahwa dominasi gempa yangterekam di hampir seluruh stasiun mempunyai arah polaritas awal gelombang P yang sama. Pada tulisanini, mekanisme sumber dideskripsikan sebagai turunan kedua tensor momen, yang didekati dengan inversiamplitudo gerak awal gelombang P di beberapa stasiun seismik. Hasil dekomposisi tensor momen didominasioleh gempa dengan persentase yang besar pada komponen ISO dan CLVD. Mekanisme fokal menunjukkanbahwa gempa-gempa yang terekam mempunyai arah jurus yang sama, yaitu arah timur laut-barat dayadengan dip sekitar 400 - 600. Sumber gempa dangkal frekuensi tinggi adalah berupa tensile-shear crack ataukombinasi antara rekahan dan sesar geser.Kata kunci: tensor momen, mekanisme sumber, frekuensi, gelombang P, polaritas, gerak awal10 hlm