THE DETERMINATION OF 2018 LOMBOK EARTHQUAKE CHAIN’S MAIN HYPOCENTER LOCATIONS THROUGH THE USE OF WAVEFORM CROSS-CORRELATION DATA

• Main Author: Sofyan Laksmana, Zakaria
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/41816
• Institution: Institut Teknologi Bandung

The island of Lombok is one of the many islands situated in the Eastern Sunda Arc which was formed by active plate subductions with a high amount of regional tectonic activities observed to this day. Amongst all of these tectonic occurences, the one that caught the most attention as of late is the Lombok earthquake chain that struck in the middle of 2018 which had caused a great amount of material damage and physical casualties. Within the earthquake chain itself, the one that was reported to be the most devastating one is the 5th of August earthquake with a moment magnitude of Mw6.9 (according to USGS’ report) in which this earthquake has been reported to possibly be linked to the previous 29th of July earthquake with a moment magnitude of 6.4 (USGS) and the following two earthquakes on the 19th of August with a moment magnitude of 6.3 (USGS) and 6.9 (USGS) respectively. In this research, the initial arrival time data fetched from a total of 26 IRIS observation stations within a distance limit of <50° to the initial earthquake source were to be corrected using an auto-picking script in which the corrected arrival time data would then be used as a reference in the waveform cross-correlation process. Afterwards, the result of the waveform cross-correlation process would then be utilized as an input within the hypocenter determination process using NonLinLoc’s oct-tree importance sampling algorithm based on the AK135-F velocity model. The newly obtained event locations indicated that the two earthquakes on the 19th of August were possibly connected through a certain fault segment with a W-E orientation, in which at a larger scale the four events’ new locations were now much more concentrated within an area that experiences the most intense shake as indicated by BNPB’s report.