Gravity Structure around Mt. Pandan, Madiun, East Java, Indonesia and Its Relationship to 2016 Seismic Activity

Abstract

Java Island is part of the island arc influenced by subducting Indo-Australian beneath Eurasian tectonic plates, therefore there is high seismic activity and an active volcanic chain trending East-West. One of the volcanoes in Java Island is Mt. Pandan, northern part of Madiun, East Java region, which is known as one of the dormant volcano in the region. According to the list of volcanoes in Indonesia Mt. Pandan is not classified as an active volcano. The previous studies mentioned that Mt. Pandan is a modern volcano which is located in the Kendeng zone. On June 25, 2015, there was felt earthquake (M 4.2) causing several houses damaged around Mt. Pandan as reported by Agency for Meteorology, Climatology, Geophysics (BMKG), Indonesia and then in February 2016, more than twenty small earthquakes (M < 4) occurred again in the area. In order to understand the structure beneath Mt. Pandan, we have conducted gravity measurement and seismicity analysis through hypocenter relocation. Our results show prominent low gravity and density anomalies by forward modeling derived from residual anomaly around Mt. Pandan area. The clusters of small earthquakes appear at depths of less than 30 km beneath Mt. Pandan. The selected focal mechanism of the event in the area is left-lateral faulting in the north and oblique dominant thrust in the south of Mt. Pandan. Some indications related to submagmatic activities such as hot springs and warm ground is found. Our interpretation is this phenomenon may be related to tectonic and magmatic activities. On the other hand, it confirms also that Mt. Pandan is probably a modern volcanic center.

Terrain Correction in Gravity Data Processing using Hybrid Land Survey and Shuttle Radar Topography Mission Digital Elevation Model: A Case Study in Mount Pandan, Indonesia

“…This area is about 40 km northeast of Madiun city. Smyth et al have defined mount Pandan as a modern volcanic center [4], which is confirmed by Santoso et al in the previous study [5]. The subsurface conditions in this area are interesting to investigate because they have a tectonic and magmatic activity that might be correlated with the magma source.…”

P- and S-wave Velocity Structures and the Influence of Volcanic Activities in the East Java Area from Seismic Tomography

“…Further to the north, a low density anomaly was observed beneath Mt. Pandan (Santoso et al 2018), suggested as the presence of hot material because of the hot springs and warm ground. Small earthquakes were observed (M < 4), which are concentrated beneath Mt.…”

“…Pandan at the depth of less than 10 km dipping to the southward. Santoso et al (2018) suggested that the small earthquakes, which occurred in 2016, may lead to the Kendeng fault activity located northward of Mt. Pandan.…”

Analysis of swarm earthquakes around Mt. Agung Bali, Indonesia prior to November 2017 eruption using regional BMKG network

“…Pandan (Santoso et al 2018), Jailolo volcano (Nugraha et al 2018a), Bekancan (Nugraha et al 2018b), the southern part of Garut, West Java (Supendi et al 2018), West Halmahera (Nugraha et al 2017b) among many others. Albino et al (2019) suggested that the dike intrusion between neighboring arc volcanoes was responsible for the Mt.…”