An attempt to Model Final Reservoir at Mt. Merapi Using Receiver Function
Keywords
Synthetic Receiver Function, Gunung Merapi, Reservoir Magma, Low Velocity ZoneAbstract
Studi di daerah Gn. Merapi sudah banyak dilakukan sebelumnya untuk mengetahui kondisi di bawah permukaan pada area tersebut, khususnya untuk mengetahui mekanisme vulkanik dari Gn. Merapi itu sendiri. Hal yang sering menjadi topik pembahasan pada studi di Gn. Merapi adalah kondisi dari reservoir magma yang ada di bawah permukaan. Untuk memperkirakan hal tersebut dilakukan teknik receiver function dengan membuat model kecepatan sintetik yang kemudian diolah menjadi kurva synthetic receiver function. Hasil synthetic receiver function kemudian dikorelasikan dengan hasil receiver function observasi hingga didapatkan korelasi yang paling baik. Sebelum dilakukan pembuatan synthetic receiver function untuk mencitrakan kondisi bawah permukaan Gn. Merapi, perlu dilakukan terlebih dahulu analisis awal terhadap respon hasil receiver function dari model sederhana yang dibuat dengan memberikan sumber-sumber sinyal utama pada kurva receiver function yang dihasilkan agar mempermudah pembuatan model kecepatan sintetik. Sumber-sumber respon sinyal utama yang mempengaruhi bacaan receiver function di antaranya adalah kontras nilai kecepatan gelombang seismik terutama Vs, adanya lapisan sedimen yang memiliki ketebalan tipis, adanya zona berkecepatan rendah (low velocity zone) yang diinterpretasikan sebagai reservoir magma, dan kedalaman dari batas kerak dan mantel atas yaitu moho discontinuity. Berdasarkan hasil synthetic receiver function di stasiun ME25, ME32 dan ME36, didapatkan kedalaman dari moho berkisar antara 26-29 km dan semakin dangkal ke arah Gn. Merapi, yaitu arah selatan dari daerah studi. Kedalaman dari low velocity zone juga bervariasi yaitu berkisar antara 5-15 km dan juga semakin dangkal ke arah selatan.
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