Modeling the density at Merapi volcano area, Indonesia, via the inverse gravimetric problem

Abstract

[1] Merapi is a high-risk andesitic volcano in Central Java, Indonesia. Very little information is known about the detailed regional density structure around Merapi and its neighbor volcano Merbabu. We compute a subsurface three-dimensional (3-D) model of anomalous density for the volcanoes Merapi and Merbabu in Central Java, Indonesia, by inversion of the gravity field. As input for the inversion methodology, gravity observations from 443 points, whose 3-D coordinates are determined by GPS, are used. The inversion algorithm is based on an explorative approach to fit a least squares condition, including a balancing factor between the minimization of the residuals and the anomalous mass. A mean density about 2242 kg/m 3 for the region of Merapi and Merbabu has been computed by least squares adjustment. Results of the inversion show major low-density contrasts up to À242 kg/m 3 and positive structures about +264 kg/m 3 , referred to the determined mean density. A density anomaly (relative high) with densities up to +264 kg/m 3 is connecting the volcanoes in a 152°course from NW to SE and might be built of older basaltic lava. Low-density contrasts about À242 kg/m could be found in agreement with magnetotelluric and electromagnetic results. Generally, the identified highand low-density bodies are in agreement with the results of other geophysical methods such as electromagnetic and magnetotelluric prospecting or geological formations and structures. A porosity about 21% is derived for the largest negative density bodies about À242 kg/m 3 . Furthermore, the density model gives some new information about the controversial origin of a hill formation near Merapi and is also used to discuss the possible existence of a shallow magma chamber, which is also a controversial subject. Generally, the density model serves as basic information for the interpretation of geodetic and geophysical observations and confirms existing results from magnetotellurics, electromagnetics, and seismic data interpretation.Components: 6265 words, 8 figures.

Volcano-tectonic control of Merapi's lava dome splitting: The November 2013 fracture observed from high resolution TerraSAR-X data

“…Both viewing geometries, ascending and descending, depict a predominant NNW-SSE trend. data and three dimensional density model simulations revealed the presence of a density contrast oriented NNW-SSE along the MerapiMerbabu trend (Tiede et al, 2005). Possibly a larger intrusive body is geologically connecting these volcanoes (Tiede et al, 2005).…”

P and S velocity structure of the crust and the upper mantle beneath central Java from local tomography inversion

“…On the basis of modeling using GPS and tilt data, Beauducel and Cornet [1999] conclude that the feeding magma reservoir can be located between 6 km and 9 km below the summit. High‐resolution gravity modeling in [ Tiede et al , 2005] also show the evidence of high‐density bodies beneath the volcanic summits of Merapi, Merbabu and Telemoyo, that can be interpreted as magma reservoirs.…”

SAR- and gravity change-based characterization of the distribution pattern of pyroclastic flow deposits at Mt. Merapi during the past 10 years

“…Merapi by inversion analysis of gravimetric data (Tiede et al 2005) can also be used to validate the dipping conduit model. The data used were Bouguer-corrected free-air gravity anomalies at the 443 observation points at Mt.…”

“…The eruptive activity is characterized by dome growth followed by extrusion of large amounts of pyroclastic flows. The dome is formed around the summit by an increase in magma viscosity, following the slow ascent of the andesitic magma from the shallow magma reservoir located at about 0.8-1.8 km depth (Tiede et al 2005). The fully grown lava dome finally collapses, decomposing into gravel-sized clasts that cause fluidized flows mixed with volcanic gasses and ash to rapidly descend toward the lower terrain (Takahashi and Tsujimoto 2000).…”