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The 1674 Ambon Tsunami: Extreme Run-Up Caused by an Earthquake-Triggered Landslide

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We present an analysis of the oldest detailed account of tsunami run-up in Indonesia, that of the 1674 Ambon tsunami (Rumphius in Waerachtigh Verhael van de Schuckelijcke Aerdbebinge, BATAVIA, Dutch East Indies, 1675). At 100 m this is the largest run-up height ever documented in Indonesia, and with over 2300 fatalities even in 1674, it ranks as one of Indonesia’s most deadly tsunami disasters. We consider the plausible sources of earthquakes near Ambon that could generate a large, destructive tsunami, including the Seram Megathrust, the South Seram Thrust, and faults local to Ambon. We conclude that the only explanation for the extreme run-up observed on the north coast of Amon is a tsunami generated by an earthquake-triggered coastal landslide. We use a two-layer tsunami model to show that a submarine landslide, with an approximate volume of 1 km³, offshore the area on Ambon’s northern coast, between Seith and Hila, where dramatic changes in coastal landscape were observed can explain the observed tsunami run-up along the coast. Thus, the 1674 Ambon tsunami adds weight to the evidence from recent tsunamis, including the 1992 Flores, 2018 Palu and Sunda Strait tsunamis, that landslides are an important source of tsunami hazard in Indonesia.
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The 1674 Ambon Tsunami: Extreme Run-Up Caused by an Earthquake-Triggered Landslide
IGNATIUS RYAN PRANANTYO
1
and PHIL R. CUMMINS
1
Abstract—We present an analysis of the oldest detailed
account of tsunami run-up in Indonesia, that of the 1674 Ambon
tsunami (Rumphius in Waerachtigh Verhael van de Schuckelijcke
Aerdbebinge, BATAVIA, Dutch East Indies, 1675). At 100 m this
is the largest run-up height ever documented in Indonesia, and with
over 2300 fatalities even in 1674, it ranks as one of Indonesia’s
most deadly tsunami disasters. We consider the plausible sources of
earthquakes near Ambon that could generate a large, destructive
tsunami, including the Seram Megathrust, the South Seram Thrust,
and faults local to Ambon. We conclude that the only explanation
for the extreme run-up observed on the north coast of Amon is a
tsunami generated by an earthquake-triggered coastal landslide. We
use a two-layer tsunami model to show that a submarine landslide,
with an approximate volume of 1 km
3
, offshore the area on
Ambon’s northern coast, between Seith and Hila, where dramatic
changes in coastal landscape were observed can explain the
observed tsunami run-up along the coast. Thus, the 1674 Ambon
tsunami adds weight to the evidence from recent tsunamis,
including the 1992 Flores, 2018 Palu and Sunda Strait tsunamis,
that landslides are an important source of tsunami hazard in
Indonesia.
Keywords: Eastern Indonesia, Ambon, tsunami hazard,
landslide.
1. Introduction
Eastern Indonesia, and the Banda Sea in particu-
lar, is a region of very active and complex tectonics
(Hamilton 1979; McCaffrey 1988; Spakman and Hall
2010; Pownall et al. 2013). Despite a historical
record rich in major, destructive earthquakes and
tsunamis, during the more recent era of instrumental
seismology most of the major events have occurred in
western Indonesia. The only way to better understand
the tsunami threat in eastern Indonesia is therefore to
glean as much information as we can from the his-
torical record, which often consists of accounts that
are sparse and difficult to interpret.
The oldest detailed tsunami account in Indonesia
was documented by Rumphius (1675). A devastating
earthquake rocked Ambon and its surrounding islands
on 17 February 1674. The earthquake was followed
by a massive tsunami about 100 m in run-up height
which was only observed on the northern coast of
Ambon Island while other areas experienced only
minor tsunamis. The earthquake and tsunami caused
more than 2300 fatalities, mostly on the northern
shore of Ambon.
The source of the tsunami and earthquake is
unknown. Løvholt et al. (2012) and Harris and Major
(2017) speculated that it was triggered by an earthquake
from south of Ambon and a landslide triggered by an
earthquake from inside Ambon Bay, respectively.
However, no attempt has been made to investigate this
event further, particularly to answer why the extreme
run-up was observed only on the northern coast of
Ambon. Therefore, the primary source of the tsunami
and earthquake remains open to question.
In the following sections of this paper, the tec-
tonic setting around Ambon is discussed first,
followed by our interpretation of the accounts of this
event. The primary source of the earthquake and
tsunami is investigated through analysis of the
Rumphius document. Tsunami modelling is then
performed to confirm the analysis. Lastly, the result
of the analysis and the implications of the findings are
discussed.
2. Tectonic Setting Around Ambon
Ambon is a small volcanic island that lies south-
west of Seram Island (Fig. 1). It consists of two small
1
Research School of Earth Sciences, Australian National
University, Canberra, Australia. E-mail: ryan.pranantyo@anu.edu.
au; phil.cummins@anu.edu.au
Pure Appl. Geophys. 177 (2020), 1639–1657
Ó2019 Springer Nature Switzerland AG
https://doi.org/10.1007/s00024-019-02390-2 Pure and Applied Geophysics
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
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A complete suite of closed analytical expressions is presented for the surface displacements, strains, and tilts due to inclined shear and tensile faults in a half-space for both point and finite rectangular sources. These expressions are particularly compact and free from field singular points which are inherent in the previously stated expressions of certain cases. The expressions derived here represent powerful tools not only for the analysis of static field changes associated with earthquake occurrence but also for the modeling of deformation fields arising from fluid-driven crack sources.
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Tsunamis caused by submarine landslides are not accompanied by seismic waves and thus may appear at the coast without warning. In this study, detailed bathymetric surveys with a multi-narrow beam echo sounder were used to map submarine landslides on the continental shelf near Cape Muroto, in the Nankai trough off southwestern Japan. One of the surveyed submarine landslides was selected to supply dimensions for the simulation of a submarine mass movement by a two-layer flow model in which the upper and lower layers correspond to seawater and turbidity currents, respectively. The time series of seafloor deformation during this simulated landslide was used as the boundary condition to drive a tsunami simulation. The results showed strong directivity effects during tsunami generation in which pushing-dominant (positive) tsunami waves propagated seaward, in the direction of the submarine landslide, and pulling-dominant (negative) tsunami waves propagated landward. Both types of waves were strongly modified by frequency dispersion. For pulling-dominant waves, a tsunami simulation that included dispersion (Boussinesq) terms predicted greater maximum tsunami heights than a non-dispersive tsunami simulation. To avoid underestimation of tsunami heights, we recommend including dispersion terms when modeling tsunamis caused by submarine landslides for disaster planning purposes.
Article
In this study, we considered the accurate calculation of far-field tsunami waveforms by using the shallow water equations and accounting for the effects of Boussinesq dispersion, seawater density stratification, elastic loading, and gravitational potential change in a finite difference scheme. By comparing numerical simulations that included and excluded each of these effects with the observed waveforms of the 2011 Tohoku tsunami, we found that all of these effects are significant and resolvable in the far field by the current generation of deep ocean-bottom pressure gauges. Our calculations using previously published, high-resolution models of the 2011 Tohoku tsunami source exhibited excellent agreement with the observed waveforms to a degree that has previously been possible only with near-field or regional observations. We suggest that the ability to model far-field tsunamis with high accuracy has important implications for tsunami source and hazard studies.
Article
Eastern Indonesia is the site of intense deformation related to convergence between Australia, Eurasia, the Pacific and the Philippine Sea Plate. Our analysis of the tectonic geomorphology, drainage patterns, exhumed faults and historical seismicity in this region has highlighted faults that have been active during the Quaternary (Pleistocene to present day), even if instrumental records suggest that some are presently inactive. Of the 27 largely onshore fault systems studied, 11 showed evidence of a maximal tectonic rate and a further five showed evidence of rapid tectonic activity. Three faults indicating a slow to minimal tectonic rate nonetheless showed indications of Quaternary activity and may simply have long interseismic periods. Although most studied fault systems are highly segmented, many are linked by narrow (<3 km) step-overs to form one or more long, quasi-continuous segment capable of producing M>7.5 earthquakes. Sinistral shear across the soft-linked Yapen and Tarera–Aiduna faults and their continuation into the transpressive Seram fold–thrust belt represents perhaps the most active belt of deformation and hence the greatest seismic hazard in the region. However, the Palu–Koro Fault, which is long, straight and capable of generating super-shear ruptures, is considered to represent the greatest seismic risk of all the faults evaluated in this region in view of important strike-slip strands that appear to traverse the thick Quaternary basin-fill below Palu city.
Article
The Weber Deep—a 7.2-km-deep forearc basin within the tightly curved Banda arc of eastern Indonesia—is the deepest point of the Earth’s oceans not within a trench. Several models have been proposed to explain the tectonic evolution of the Banda arc in the context of the ongoing (ca. 23 Ma–present) Australia–Southeast Asia collision, but no model explicitly accounts for how the Weber Deep achieved its anomalous depth. Here we propose that the Weber Deep formed by forearc extension driven by eastward subduction rollback. Substantial lithospheric extension in the upper plate was accommodated by a major, previously unidentified, low-angle normal fault system we name the “Banda detachment.” High-resolution bathymetry data reveal that the Banda detachment is exposed underwater over much of its 120 km down-dip and 450 km lateral extent, having produced the largest bathymetric expression of any fault discernable in the world’s oceans. The Banda arc is a modern analogue for highly extended terranes preserved in the many regions that may similarly have “rolled open” behind migrating subduction zones.