Tsunami hazard in Lombok and Bali, Indonesia, due to the Flores back-arc thrust
<p>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 <span class="inline-formula">∼250</span> km to the south of the island...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-05-01
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| Series: | Natural Hazards and Earth System Sciences |
| Online Access: | https://nhess.copernicus.org/articles/22/1665/2022/nhess-22-1665-2022.pdf |
| Summary: | <p>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 <span class="inline-formula">∼250</span> 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 <span class="inline-formula"><i>M</i><sub>w</sub></span> 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 <span class="inline-formula">≥<i>M</i><sub>s</sub></span> 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 <span class="inline-formula"><i>M</i><sub>w</sub></span> 7.2–7.9<span class="inline-formula">+</span>) 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 <span class="inline-formula"><i><</i>9</span> min and Denpasar in <span class="inline-formula">∼</span> 23–27 min, with multiple waves. For an earthquake with 3–5 m of
coseismic slip, Mataram and Denpasar experience maximum wave heights of
<span class="inline-formula">∼</span> 1.6–2.7 and <span class="inline-formula">∼</span> 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 <span class="inline-formula">∼</span> 55–140 m inland along the northern coast and
<span class="inline-formula">∼230</span> m along the southern coast, with maximum flow depths of
<span class="inline-formula">∼</span> 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.</p> |
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| ISSN: | 1561-8633 1684-9981 |