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

Characteristic of Lokon Volcano Deformation of 2009 - 2011 Based on GPS Data

DOI: 10.17014/ijog.v7i4.147Precursor of Lokon Volcano eruptions in 2011 is believed to begin since December 2007 which was marked by increasing number of volcanic earthquakes and gas emission. To support this information, deformation method is used primarily to determine deformation characteristics of Lokon volcanic activity in the period of 2009-2011. The period of analysis is adapted to the presence of GPS data. Displacement rate of Lokon GPS observation points in the period of 2009 - 2011 ranged from 1.1 to 7 cm a year. Strain patterns that occur in the areas are compression surrounding Tompaluan crater and extension in the eastern slope. Location of the pressure source for August 2009 - March 2011 measurement was at a depth of 1800 m beneath Tompaluan crater. Deformation in the Lokon Volcano is characteristized by the compression zone in the summit and crater area caused by magma activity raised into the surface from a shallow magma source which is accompanied by a high release of volcanic gases. Accumulated pressure release and deformation rate as measured in the Lokon Volcano remain low

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

Penerapan Metode Permanent Scatterers Interferometry Synthetic Aperture Radar (PS-InSAR) untuk Analisis Deformasi Gunungapi (Studi Kasus : Gunungapi Sinabung)

Di Indonesia terdapat 129 gunungapi yang masih aktif, salah satunya adalah Gunungapi Sinabung. Sepanjang tahun 2017 tercatat Gunungapi Sinabung mengalami erupsi-erupsi kecil akibat aktivitas magma. Pada gunungapi yang sedang aktif akan terjadi Perubahan bentuk permukaan tanah yang disebut sebagai deformasi permukaan. Untuk memantau deformasi dapat digunakan berbagai macam metode, antara lain metode geodetik dengan menggunakan pengamatan GPS dan pengolahan data SAR dengan teknik PS-InSAR. Penelitian ini dilakukan untuk mengetahui deformasi yang terjadi pada gunungapi menggunakan metode PS-InSAR dengan validasi menggunakan data GPS. Data SAR yang digunakan, terdiri dari 27 citra Sentinel 1A tipe SLC dengan tanggal akuisisi 2 Januari hingga 28 Desember 2017. Hasil dari PS-InSAR menunjukkan line of sight (LOS) velocity rate yang terjadi berkisar pada -40,400 mm/tahun sampai dengan 30,800 mm/tahun dengan simpangan baku berkisar pada 1,400 mm/tahun sampai dengan 31,800 mm/tahun

The 2017-19 activity at Mount Agung in Bali (Indonesia) : intense unrest, monitoring, crisis response, evacuation , and eruption

After 53 years of quiescence, Mount Agung awoke in August 2017, with intense seismicity, measurable ground deformation, and thermal anomalies in the summit crater. Although the seismic unrest peaked in late September and early October, the volcano did not start erupting until 21 November. The most intense explosive eruptions with accompanying rapid lava effusion occurred between 25 and 29 November. Smaller infrequent explosions and extrusions continue through the present (June 2019). The delay between intense unrest and eruption caused considerable challenges to emergency responders, local and national governmental agencies, and the population of Bali near the volcano, including over 140,000 evacuees. This paper provides an overview of the volcanic activity at Mount Agung from the viewpoint of the volcano observatory and other scientists responding to the volcanic crisis. We discuss the volcanic activity as well as key data streams used to track it. We provide evidence that magma intruded into the mid-crust in early 2017, and again in August of that year, prior to intrusion of an inferred dike between Mount Agung and Batur Caldera that initiated an earthquake swarm in late September. We summarize efforts to forecast the behavior of the volcano, to quantify exclusion zones for evacuations, and to work with emergency responders and other government agencies to make decisions during a complex and tense volcanic crisis