Detailed seismic imaging of Merapi volcano, Indonesia, from local earthquake travel-time tomography

Mt. Merapi, located in central Java, Indonesia, is one of the most active volcanoes in the world. It has been subjected to numerous studies using a variety of methods, including tomographic imaging, in an attempt to understand the structure and dynamics of its magmatic plumbing system. Results of previous seismic tomographic studies that include Mt. Merapi poorly constrain the location of its underlying magma source due to limited data coverage. In order to comprehensively understand the internal structure and magmatism of Mt. Merapi, a project called DOMERAPI was conducted, in which 53 broadband seismic stations were deployed around Mt. Merapi and its neighbourhood for approximately 18 months, from October 2013 to April 2015. In this study, we compare Vp, Vs, and Vp/Vs tomograms constructed using data obtained from local (DOMERAPI) and regional seismic networks with those obtained without DOMERAPI data. We demonstrate that the data from the DOMERAPI seismic network are crucial for resolving key features beneath the volcano, such as high Vp/Vs ratios beneath the Merapi summit at similar to 5 km and similar to 15 km depths, which we interpret as shallow and intermediate magma bodies, respectively. Furthermore, west-east vertical sections across Mt. Merapi, and a "dormant" (less active) volcano, Mt. Merbabu, exhibit high Vp/Vs and low Vp/Vs ratios, respectively, directly beneath their summits. This observation likely reflects the presence (for Mt. Merapi) and absence (for Mt. Merbabu) of shallow magma bodies near the surface.