Tomografi Kecepatan Seismik 3D Daerah Danau Toba Menggunakan SimulPS12

Novia Anggraini, Dwi Pujiastuti, Atin Nur Aulia

Abstract


Gunung Toba adalah salah satu gunung purba di Indonesia yang berada di Sumatera Utara. Terdapat dua aktivitas yang mempengaruhi gunung tersebut, yaitu aktivitas vulkanik yang berasal dari magma di bawahnya dan aktivitas tektonik yang berasal dari subduksi Lempang Indo-australia. Meskipun sudah lebih dari 70.000 tahun sejak terakhir kali erupsi dan menyebabkan terbentuknya kaldera vulkano-tektonik tersebar di dunia, yaitu Kaldera Toba, aktivitas-aktivitas tersebut masih ada. Salah satu hal yang dapat dilakukan untuk mengetahui keadaan di bawahnya adalah dengan melakukan tomografi kecepatan seismik 3D. Pada penelitian ini, program yang digunakan adalah SimulPS12 dan menghasilkan tomogram anomali Vp, Vs dan rasio Vp/Vs.  Berdasarkan hasil tomografi tersebut diketahui bahwa zona lemah terdapat pada kedalaman 30 km di bagian tengah Danau Toba dan kedalaman 50 km. Adapun proses partial melting terjadi pada kedalaman sekitar 130 km hingga 50 km yang berasal dari slab subduksi di bawah Danau Toba.  Pada kedalaman 30 km, selain anomali negatif, juga terlihat pola anomali Vp dan Vs positif yang mengindikasikan keberadaan bekas konduit dari intrusi magma yang membeku. Selain itu, aktivitas seismik juga terlihat tersebar pada beberapa titik di sekitar Kaldera Toba seperti di Gunung Pusuk Buhit dan Gunung Pardepur.

 

Toba volcano is one of the ancient volcanoes in Indonesia located in Northern Sumatera.  There were two activities having an affect on the volcano, the volcanic activity from the magma chamber beneath the Toba caldera complex and the tectonic activity from the subduction of Indo-Australia Plate. Despite the last eruption of Toba was about 70.000 years ago, the activities were still exist.  The 3D seismic tomography could be carried out to understand the conditions beneath Toba Caldera.  In this research, the data was processed using the SimulPS12 program, and tomography images obtained were from Vp, Vs, and Vp/Vs ratio.  The results showed that the weak zones were found in the depth of 30 km in the middle part of Toba Caldera and the depth of 50 km. The partial melting process was in the depth of about 130 km to 50 km beneath Toba Caldera. The depth of 30 km was also found the high anomaly of Vp and Vs which indicated the existence of the remnant conduit of solidified magma.  In addition, the other seismic activities could also be found in its vicinity, i. e., in Pusuk Buhit Volcano and Pardepur Volcano.


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DOI: https://doi.org/10.25077/jfu.9.4.457-464.2020

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