High seismicity rates in and around West Java and Sumatra occur as a result of the Indo-Australian plate converging with and subducting beneath the Sunda plate. Large megathrust events associated with this process likely pose a major earthquake and tsunami hazard to the surrounding community, but further effort is required to help understand both the likelihood and frequency of such events. With this in mind, we exploit catalog seismic data sourced from the Agency for Meteorology, Climatology, and Geophysics (BMKG) of Indonesia and the International Seismological Centre (ISC) for the period April 2009 through to July 2020, in order to conduct earthquake hypocenter relocation using a teleseismic double-difference method. Our results reveal a large seismic gap to the south of West Java and southeast Sumatra, which is in agreement with a previous GPS study that finds the region to be a potential future source of megathrust earthquakes. To investigate this further, tsunami modeling was conducted in the region for two scenarios based on the estimated seismicity gaps and the existence of a backthrust fault. We show that the maximum tsunami height could be up to 34 m along the west coast of southernmost Sumatra and along the south coast of Java near the Ujung Kulon Peninsula. This estimate is comparable with the maximum tsunami height predicted by a previous study of southern Java in which earthquake sources were derived from the inversion of GPS data. However, the present study extends the analysis to southeast Sumatra and demonstrates that estimating rupture from seismic gaps can lead to reliable tsunami hazard assessment in the absence of GPS data.
The article "On the potential for megathrust earthquakes and tsunamis off the southern coast of West Java and southeast Sumatra, Indonesia", written by
<p>Secara tektonik, zona subduksi di utara Gorontalo berpotensi menimbulkan gempa bumi yang dapat mengakibatkan tsunami. Kajian statistik seismisitas menunjukkan adanya indikasi celah kegempaan di wilayah tersebut dengan Magnitudo maksimum sebesar 8,2 Mw. Pemodelan tsunami dilakukan untuk mengestimasi ketinggian <em>run up</em> tsunami di pesisir pantai dan luasan daerah genangan tsunami sebagai upaya mitigasi bencana tsunami di Desa Dulukapa dan Deme 1. Pemodelan tsunami menggunakan teori gelombang linier di laut dalam dan gelombang perairan dangkal pada perairan dengan kedalaman dangkal dan daerah landaan dengan grid yang konstan dengan bantuan aplikasi TUNAMI-N2. Gempa bumi yang digunakan untuk pemodelan merupakan skenario terburuk berdasarkan tatanan tektonik dan sejarah kegempaan wilayah penelitian. Data yang digunakan meliputi data batimetri GEBCO (<em>General Bathymetric Chart Of The Ocean</em>) grid<em> </em>30 <em>arc second</em> dan topografi SRTM (<em>Shuttle Radar Topography Mission</em>) <em>grid</em> 1 <em>arc second</em><em> </em>yang dikeluarkan oleh USGS. Selanjutnya, data gempa bumi dan tsunami masing-masing diperoleh dari katalog gempa bumi <em>Advanced Nasional Seismic System</em> (ANSS) dan Badan Meteorologi Klimatologi dan Geofisika (BMKG). Hasil penelitian menunjukkan waktu penjalaran gelombang dari episenter ke pantai utara Desa Dulukapa 18,2–13,8 menit dengan <em>run up </em>9,8–13,8 m dan jarak terjauh landaan tsunami sejauh 800 m. Sementara itu, waktu tiba tsunami di Desa Deme 1 sekitar 18,8–23,83 menit dengan <em>run up <br /> </em>10,76–15,1 m, dan jarak terjauh landaan tsunami sejauh 830 m. Luasan daerah landaan tsunami mencapai 1900 m² pada kedua desa tersebut. Kedua desa tersebut merupakan wilayah yang rawan terdampak tsunami sehingga perlu dilakukan upaya mitigasi bahaya tsunami untuk mengurangi resiko yang ditimbulkan.</p>
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