ORCID Profile
0000-0003-0406-803X
Current Organisation
Nanyang Technological University
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Publisher: Seismological Society of America (SSA)
Date: 09-11-2021
DOI: 10.1785/0120210154
Abstract: The frontal sections of subduction zones are the source of a poorly understood hazard: “tsunami earthquakes,” which generate larger-than-expected tsunamis given their seismic shaking. Slip on frontal thrusts is considered to be the cause of increased wave heights in these earthquakes, but the impact of this mechanism has thus far not been quantified. Here, we explore how frontal thrust slip can contribute to tsunami wave generation by modeling the resulting seafloor deformation using fault-bend folding theory. We then quantify wave heights in 2D and expected tsunami energies in 3D for both thrust splays (using fault-bend folding) and down-dip décollement ruptures (modeled as elastic). We present an analytical solution for the d ing effect of the water column and show that, because the narrow band of seafloor uplift produced by frontal thrust slip is d ed, initial tsunami heights and resulting energies are relatively low. Although the geometry of the thrust can modify seafloor deformation, water d ing reduces these differences tsunami energy is generally insensitive to thrust r parameters, such as fault dip, geological evolution, sedimentation, and erosion. Tsunami energy depends primarily on three features: décollement depth below the seafloor, water depth, and coseismic slip. Because frontal ruptures of subduction zones include slip on both the frontal thrust and the down-dip décollement, we compare their tsunami energies. We find that thrust r s generate significantly lower energies than the paired slip on the décollement. Using a case study of the 25 October 2010 Mw 7.8 Mentawai tsunami earthquake, we show that although slip on the décollement and frontal thrust together can generate the required tsunami energy, & % was contributed by the frontal thrust. Overall, our results demonstrate that the wider, lower litude uplift produced by décollement slip must play a dominant role in the tsunami generation process for tsunami earthquakes.
Publisher: Copernicus GmbH
Date: 18-05-2022
DOI: 10.5194/NHESS-22-1665-2022
Abstract: Abstract. The tsunami hazard posed by the Flores back-arc 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 r 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 local tsunamis along the northern coast of Lombok. 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+) using deterministic modeling, 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, together with a high-resolution bathymetry dataset developed by combining direct measurements from the General Bathymetric Chart of the Oceans (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 min and Denpasar in ∼ 23–27 min, with multiple waves. For an earthquake with 3–5 m of coseismic slip, Mataram and Denpasar experience maximum wave heights of ∼ 1.6–2.7 and ∼ 0.6–1.4 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 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.
Publisher: Copernicus GmbH
Date: 20-11-2021
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 r 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.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-10851
Abstract: Both retrospective tsunami analyses and assessments of future tsunami hazards depend on accurate modeling of how tsunami waves generated offshore propagate through shallow waters near the coast. Accurate models of tsunami propagation in shallow water require high-resolution bathymetric maps, but these are often inaccessible because of the time and cost required to acquire them. In addition, tsunami models based on high resolution bathymetry have high computational processing requirements. Hence, it has been common to use globally available datasets with coarser resolutions, such as the GEBCO dataset, in modeling.Here, we examine how variations in bathymetric resolution, from 5 m to & #8764 m (GEBCO), affect simulated coastal tsunamis. Our case study includes four study sites with available LiDAR bathymetry datasets (1 m resolution). At each site 30 sets of points were randomly extracted from the LiDAR bathymetry datasets and used to generate bathymetric grids with resolutions of 5, 10, 20, 30, 40, 50, 100, 200, and 300 m at each site. These were also compared to a bathymetry based purely on the GEBCO dataset for that region (& #8764 m resolution), that we modified to match the coastlines of the other bathymetry models. Tsunami waves offshore were generated by setting up an instantaneous rupture sourced from a hypothetical fault model and we used the commonly used COMCOT software to model tsunami propagation towards the coast.Using the model run with 5 m resolution bathymetry as a high resolution reference model, we observed that bathymetric grids with resolutions of 10 & #8211 50 m can reproduce coastal wave heights reasonably well, with the maximum wave height overestimated by & #8804 % or underestimated by & #8804 %. For coarser bathymetric grids, however (& #8805 m resolution), there is an increasing trend of underestimation. Wave heights are underestimated by at least 10% and with up to 30%, 40% and 60% underestimation for bathymetric resolutions of 100, 200, and 300 m, respectively. Notably, the commonly used GEBCO model underestimated coastal tsunami heights by as much as 70%. We also examined the impact on tsunami arrival time: and found that resolutions of 10 & #8211 50 m exhibited a first wave arriving & #8764 % earlier than expected, while coarser resolutions showed more variability, with the first wave arriving either & #8804 % later or & #8804 % earlier. For GEBCO-based models, the& arrival time estimate tends to be underestimated by 10 & #8211 30% or overestimated by 20 & #8211 50%. Our study demonstrates that using GEBCO bathymetry in numerical modeling of tsunami wave propagation in the coastal region likely leads to a significant underestimation of the wave height, with the wave also predicted to arrive too early. However, a reasonably accurate result can be achieved using a bathymetric resolution in the 10 m & #8211 50 m range, and is achievable with reasonable computational efficiency. This study highlights the importance of shallow bathymetry in the numerical modeling of tsunami propagation.
No related grants have been discovered for Raquel Felix.