Application of Seismicity and Gravity Observation-Based Filtering Model for Mapping a Fault Structure in Weh Island, Indonesia

Aceh Province is one of the Indonesian regions prone to earthquakes beneath the Great Sumatran Fault, which has been focused mapped on the land. At the same time, the continuity of the Great Sumatran Fault to the marine and islands is rarely investigated. We apply the Gravity Model Plus which has a resolution of 200 m/px, to map a detailed structure of the the Great Sumatran Fault in Weh Island. The Bouguer anomaly varied between 32 – 78 mGal, which reveals the response of the rocks comprising Weh Island, such as those on the east side with a high-value reaction corresponding to highly dense basalts 2.84 g/cm3 and on the west side with a low-value response representing the density of andesites 2.56 g/cm3. The residual anomaly indicated several local faults, e.g., Sabang and Seuke faults located on the east side, Lhok Jeumpa on the central side, and Pria Laot on the west side. Meanwhile, the derivative data from the Bouguer anomaly could explain the fault structures corresponding to regional geological maps, such as the Sabang fault in Balohan in the northwest-southeast direction and several others controlling the Jaboi volcano, i.e., Ceunohot and Leumomate. The focal mechanism from seismicity analysis figured the fault orientation from the Seulimeum segment in the direction of NW-SE, which is essential to assess an active fault. Based on data processing, we concluded the the Gravity Model Plus data is effective for first mapping the fault structure in developing countries, such as Indonesia.