Gempa Nusantara: A New Digital Database of Felt Intensity for Historical Earthquakes in the Indonesian Archipelago

Abstract

Seismicity during Dutch colonial rule in Indonesia between 1800 and 1939 is poorly catalogued with existing summaries (e.g. Newcomb & McCann, 1987) too brief for further quantitative assessment such as the calculation of intensity magnitudes (MI). We focus on this period in Indonesian history, collating and analysing reports from official documents and newspapers from the erstwhile Dutch East Indies. We scrutinize these for macroseismic intensity using the European Macroseismic Scale (EMS-98). This scale is closely related to the Modified Mercalli Intensity (MMI) scale but is associated with better guidelines with which to assess damage to built-up environments. Our approach enables us to uniformly assess felt intensities from Sumatra, Java, Bali, and Borneo along with instances of perceived shaking from the eastern Indonesian archipelago, and from the Malay peninsula including Singapore. Building upon previous work (Martin et al., 2015), we corelate our data, when possible, with regional, and teleseismic instrumental observations. This allows us to discriminate, for example, a possible M~6 doublet in the region of South Sumatra in 1908. Felt effects in west Malaysia and Singapore from numerous earthquakes in Sumatra were also collected, and unexpectedly, we found two widely felt earthquakes in Singapore in 1922 that likely originated in the region of the southern Malaya peninsula. All our observations contribute to a database named Gempa Nusantara which roughly translates to earthquakes (gempa) in the Indonesian archipelago (nusantara) in Bahasa Indonesia. This database uses a web application called MIDOP (Macroseismic Intensity Data Online Publisher) which is an open-source program written in PHP that has been previously utilized to publish intensity data in Europe (Locati et al., 2014). In our study we extend the capabilities of the MIDOP application further, particularly in equatorial regions, and use it to manage our data from historical Indonesian earthquakes.