PENENTUAN ORIENTASI BIDANG SESAR MENGGUNAKAN FOCAL MECHANISM HIPOSENTER GEMPA MIKRO LAPANGAN PANASBUMI "GAMMA"

• Main Author: SIHOTANG, IWAN YANDIKA (Author)
• Format: Book
• Published: 2014-06-25.
• Subjects: Thesis; NonPeerReviewed
• Online Access: Link Metadata
• Keywords: L Education (General)

Lapangan Panasbumi "Gamma" terletak pada jalur gunungapi yang berasosiasi dengan lapangan panasbumi lainnya dan dikontrol oleh proses geologi serta aktivitas ekploitasi panasbumi, hal tersebut diindikasikan oleh bidang sesar lokal yang menjadi salah satu faktor pemicu gempa mikro. Identifikasi bidang sesar dengan metode focal mechanism dilakukan dengan meninjau lokasi dan relokasi hiposenter yang di dapat dari data gempa mikro, masing-masing menggunakan metode single event determination (SED) dan metode Double Difference (DD). Sebanyak 211 data dari 70.659 hiposenter pada periode Maret 2012 hingga Oktober 2012 tercatat di 5 stasiun perekam gempa mikro yang terdapat pada Lapangan Panasbumi "Gamma". Sebanyak 211 data digunakan untuk penentuan lokasi hiposenter metode SED 60 data untuk penentuan relokasi hiposenter metode DD, dan 4 data untuk penentuan solusi focal mechanism. Sebaran hiposenter hasil metode SED dan DD tersebar dari timur laut hingga barat daya Lapangan Panasbumi "Gamma". Berdasarkan hasil metode SED, distribusi hiposenter memberikan dugaan bahwa caprock berada diatas elevasi 500 meter dan reservoar panasbumi berada diantara 500 hingga -1500 (dibawah titik mean sea level). Hasil lokasi metode SED kemudian di relokasi dengan relokasi metode DD sehingga distribusi hiposenter terpusat pada 4 bidang sesar A, B, C, dan D yang berada diantara sumur produksi dan injeksi. Penentuan orientasi kempat bidang sesar dengan solusi focal mechanism ditinjau dari pergerakan awal waktu tiba gemombang P, yaitu sesar A, B, C berjenis reverse lateral oblique dan sesar D berjenis lateral strike slip. "Gamma" geothermal field is located in volcanic lines which associated by others geothermal field and controlled by geological processes as well as the activity of geothermal exploitation, so they are indicated by fault planes which became one of microearthquake's triggering factors. Fault planes identification with focal mechanism method towards michroearthquake data has been done by reviewed location and relocation of hipocenters, which used of Single Event Determination (SED) and Double Difference (DD). 211 data of 70.659 hypocenters recorded by five microearthquake recording stations in "Gamma" geothermal field during the periode March 2012 to October 2012. 211 hypocenters data used for SED location determination, 60 data for DD relocation determination, and 4 data for focal mechanism solution. Hypocenters location and relocation of SED and DD methods spread off through northwest to southwest of "Gamma" geothermal field. Based on SED method result, distribution of hypocenter shows the caprock elevation is located upon 500 meters and the geothermal reservoir is located about 500 meters to -1500 meters (beneath mean sea level point). Afterwards, the SED method result is relocated by DD method so that hypocenters distribution is centered on four fault planes, there are fault planes A, B, C and D which are located between production and injection wells. Determination of all fault planes obtained with focal mechanism solution which reviewed by initial movement of P waves arrival time, it indicate A, B, C fault planes are typed reverse lateral oblique and D fault plane is typed lateral strike slip.