Tsunami hazard in Lombok & Bali, Indonesia, due to the Flores backarc thrust

Abstract

Abstract. The tsunami hazard posed by the Flores backarc thrust, which runs along the northern coast of the islands of Bali and Lombok, Indonesia, is poorly studied compared to the Sunda megathrust, situated ~250 km to the south of the islands. However, the 2018 Lombok earthquake sequence demonstrated the seismic potential of the western Flores Thrust when a fault ramp beneath the island of Lombok ruptured in two Mw 6.9 earthquakes. Although the uplift in these events mostly occurred below land, the sequence still generated 1–2.5 m-high local tsunamis along the northern coast of Lombok (Wibowo et al., 2021). Historical records show that the Flores fault system in the Lombok and Bali region has generated at least six ≥ Ms 6.5 tsunamigenic earthquakes since 1800 CE. Hence, it is important to assess the possible tsunami hazard represented by this fault system. Here, we focus on the submarine fault segment located between the islands of Lombok and Bali (below the Lombok Strait). We assess modeled tsunami patterns generated by fault slip in six earthquake scenarios (slip of 1–5 m, representing Mw 7.2–7.9+), with a focus on impacts on the capital cities of Mataram, Lombok and Denpasar, Bali, which lie on the coasts facing the strait. We use a geologically constrained earthquake model informed by the Lombok earthquake sequence (Lythgoe et al., 2021), together with a high-resolution bathymetry dataset developed by combining direct measurements from GEBCO with sounding measurements from the official nautical charts for Indonesia. Our results show that fault rupture in this region could trigger a tsunami reaching Mataram in < 8 minutes and Denpasar in ~10–15 minutes, with multiple waves. For an earthquake with 3–5 m of coseismic slip, Mataram and Denpasar experience maximum wave heights of ~1.3–3.3 m and ~0.7 to 1.5 m, respectively. Furthermore, our earthquake models indicate that both cities would experience coseismic subsidence of 20–40 cm, exacerbating their exposure to both the tsunami and other coastal hazards. Overall, Mataram city is more exposed than Denpasar to high tsunami waves arriving quickly from the fault source. To understand how a tsunami would affect Mataram, we model the associated inundation using the 5 m slip model and show that Mataram is inundated ~55–140 m inland along the northern coast and ~230 m along the southern coast, with maximum flow depths of ~2–3 m. Our study highlights that the early tsunami arrival in Mataram, Lombok gives little time for residents to evacuate. Raising their awareness about the potential for locally generated tsunamis and the need for evacuation plans is important to help them respond immediately after experiencing strong ground shaking.

Modeling the Potential of Tsunami Hazard in Labuan Bajo Towards A Disaster-Resilient Tourism Area

“…Until now, a simulation of the propagation of the 1992 Flores tsunami located in the east of Labuan Bajo is the study conducted (Yeh et al, 1993). Afterwards, the potential for a tsunami in the north of the island of Bali, which is located west of Labuan Bajo, was simulated (Felix et al, 2021;Wibowo, Kongko, Hendriyono, & Karima, 2021). Another study showed the potential for a tsunami originating from Sletan Nusa Tenggara (Pradjoko & Muhari, 2020).…”

Source characteristics of the 2022 southwest of southern Sumatra, Indonesia earthquake (Mw 6.7) revealed by tsunami waveform data and its implication to tsunami hazard assessment

“…Therefore, we refined the GEBCO data using the Batnas data. As suggested by Felix et al (2022), we conducted a simple bathymetric data verification by comparing it with Google Earth satellite imagery to achieve good-quality data.…”

Encourage resource governance: Responding disaster threats behind environmentally friendly claims at the Tumpang Pitu gold mine

“…As an area that is prone to disasters, it is appropriate that Banyuwangi Regency needs to reflect on a number of natural disasters that have occurred in almost all regions in Indonesia, ranging from landslides, flash floods, tidal floods, hurricanes, volcanic eruptions, earthquakes, droughts, tsunamis, and so on. It is still clearly recorded in various records, major catastrophic events that occurred in 2018, such as the earthquake in Lombok Island, the tsunami in Central Sulawesi, and the tsunami in the Sunda Strait which claimed many lives and cause huge material losses (Felix et al, 2021;Fuady & Munadi, 2021;Safitri et al, 2021). A number of major disaster events that have occurred are a reminder for the government and all relevant stakeholders to continue to make improvements.…”