TOPIC 5. MULTI-HAZARD
WARNING SYSTEMS
Long-Term Ocean Observing Coupled with Community Engagement
Improves Tsunami Early Warning
By Danielle F. Sumy, Sara K. McBride, Christa von Hillebrandt-Andrade, Monica D. Kohler, John Orcutt, Shuichi Kodaira,
Kate Moran, Daniel McNamara, Takane Hori, Elizabeth Vanacore, Benoît Pirenne, and John Collins
Pressure
Gauge
0101
1
1
Tsunami
Warning
Center
Satellite
Long-Term
Seismometer
Geodetic
Transponder
Autonomous
Vehicle
DART
Tsunameter
AUV
Wave
Glider
FIGURE 1.
Schematic of ocean-based geophysical instrumentation and data
communications installation. A wave glider and a Deep-Ocean Assessment
and Reporting of Tsunamis (DART) tsunameter communicate with a satellite.
An autonomous underwater vehicle (AUV) collects data from the water col-
umn for later transmission via the satellite. Other instrumentation includes a
recoverable geodetic transponder, a trawl-resistant and current-protected
seismometer, and a self-calibrating pressure gauge.
The 2004 magnitude (M) 9.1 Sumatra-Andaman Islands
earthquake in the Indian Ocean triggered the deadliest
tsunami ever, killing more than 230,000 people. In
response, the United Nations Educational, Scientific,
and Cultural Organization (UNESCO) established three
additional Intergovernmental Coordination Groups
(ICGs) for the Tsunami and Other Coastal Hazards Early
Warning System: for the Caribbean and Adjacent Regions
(ICG/CARIBE-EWS), for the Indian Ocean, and for the
Northeastern Atlantic, Mediterranean, and Connected
Seas. Along with the ICG for the Pacific Ocean, which was
established in 1965, one of the goals of the new ICGs was
to improve earthquake and tsunami monitoring and early
warning. This need was further demonstrated by the 2011
Great East Japan (Tōhoku-oki) earthquake and tsunami,
which killed more than 20,000 people, and other destruc-
tive tsunamis that occurred in the Solomon Islands, Samoa,
Tonga, Chile, Indonesia, and Peru.
In response to the call to action by the UN Decade
of Ocean Science for Sustainable Development (2021–
2030), as well as the desired safe ocean outcome (von
Hillebrandt-Andrade et al., 2021), the Intergovernmental
Oceanographic Commission (IOC) of UNESCO approved
the Ocean Decade Tsunami Programme in June 2021. One
of its goals is to develop the capability to issue actionable
alerts for tsunamis from all sources with minimum uncer-
tainty within 10 minutes (Angove et al., 2019). While laud
-
able, this goal presents complexities. Currently, warning
depends on quick detection as well as the location and
initial magnitude estimates of an earthquake that may
generate a tsunami. Other factors that affect tsunamis,
such as the faulting mechanism (how the faults slide past
each other) and areal extent of the earthquake, currently
take at least 20–30 minutes to forecast and are still subject
to large uncertainties. Hence, agencies charged with tsu-
nami early warning need to broadcast public alerts within
minutes after an earthquake occurs but may struggle to
meet this 10-minute goal without further technological
advances, some of which are outlined in this article.
To reduce loss of life through adequate tsunami warn-
ing requires global ocean-based seismic, sea level, and
geodetic initiatives to detect high-impact earthquakes
and tsunamis, combined with sufficient communication
and education so that people know how to respond when
they receive alerts and warnings. The United Nations
70
International Strategy for Disaster Reduction defines an
early warning system as “a set of capacities needed to
generate and disseminate timely and meaningful warn-
ing information to enable individuals, communities, and
organizations threatened by a hazard to prepare and to
act appropriately and in sufficient time to reduce the pos
-
sibility of harm or loss” (UNISDR, 2012). In short, a success-
ful early warning system requires technology coupled with
human factors (Kelman and Glantz, 2014).
In this article, we explore case studies from Japan and
Canada, where scientists are leading the way in incorpo-
rating ocean observing capabilities in their early warning
systems. We also explore advancements and challenges
in the Caribbean, an area with a complex tectonic envi-
ronment that would benefit greatly from increased global
ocean observing capabilities. We also explore physical and
social science interventions necessary to reduce loss of life.
TECHNOLOGICAL CAPABILITIES
Seafloor seismometers measure Earth motions in three
dimensions across an extensive frequency band, from
tides, earthquake-caused resonances, and seismic waves
to sounds created by whales and ships (e.g., Kohler et al.,
2020; Kuna and Nábelek, 2021;
Figure 1
). Seafloor bot
-
tom pressure recorders enable detection of a tsunami
wave and its speed, direction, and wavelength, providing
information to help forecast coastal tsunami height and
duration (e.g., Rabinovich and Eblé, 2015). For instance,
Deep-ocean Assessment and Reporting of Tsunamis
autonomous underwater vehicles, and buoys closer to or
at the sea surface have helped reduce delays in delivery
of data to TWCs (
Figure 1
). Wave gliders, which look like
autonomous surfboards with collapsible propellers, use
wave and solar energy for electrical power and propulsion.
Within minutes, onboard communications systems access
orbiting satellites in order to send data from seafloor sen
-
sors to onshore collection points.
In the past two decades, Japan, Canada, and the United
States have also installed seismic and bottom pressure
recorders onto regional ocean bottom fiber-optic cable
arrays located in the Pacific Ocean. For example, in waters
off southwestern Japan in the Nankai Trough, the Japan
Agency for Marine-Earth Science and Technology (JAMSTEC)
constructed DONET, the Dense Oceanfloor Network sys
-
tem for Earthquakes and Tsunamis (Aoi et al., 2020).
DONET connects various sensors to a node (a junction that
connects sensors to a submarine cable) to provide data for
evaluating the coupling and slip behavior along the Nankai
Trough, a fault area presumed to be primed for a future
earthquake and potential tsunami (
Figures 2a and 3a
). M8
earthquakes occur at intervals of about 100–200 years at
the Nankai Trough due to the subduction of the Philippine
Sea Plate beneath the Eurasian Plate. More than 75 years
have elapsed since the last two M8+ earthquakes, the 1944
M8.1 and 1946 M8.3 events, ruptured the Nankai Trough.
The probability of an M8 earthquake occurring in this
region in the next 30 years is estimated to be more than
80% (Geological Survey of Japan, 2021).
FIGURE 2. (a) Map showing the Dense Ocean-
floor Network system for Earthquakes and Tsu-
namis (DONET) 1 station and borehole observato-
ries (Integrated Ocean Drilling P
-m/
International
Ocean Discovery Program Sites C0002, C0010,
and C0006) in the Nankai Trough, offshore
Japan. (b) Photograph of the head of the bore-
hole observatory (C0010). (c) Schematic of sen-
sors within the borehole (C0002).
(c) modified
from Kopf et al. (2011), Figure F9
C0002
C0010
C0006
C0002
Meters below the seafloor
C0010
a
b
c
DONET 1
(DART) seafloor pressure recorders (or
tsunameters) are coupled with a sepa-
rately moored buoy at the sea surface
(
Figure 1
) to send real-time data via sat-
ellite transmission to tsunami warning
centers (TWCs). The real-time transmis-
sion of data (on the order of minutes to
tens of minutes) to TWCs helps refine
the location of a potential tsunami-
generating earthquake and produce
more accurate tsunami forecasts and
warnings. Technological improvements
in acoustic data transmission from
seafloor networks to wave gliders,
71
DONET contains seismometers, pressure recorders,
and borehole observatories (
Figure 2b,c
). JAMSTEC also
constructed a seafloor geodetic network by utilizing the
DONET system as data transmission infrastructure. In the
central part of the Nankai Trough, a sensor system for
observing earthquakes, strain, tilt, and pore fluid pressure
is installed in boreholes drilled by the vessel
Chikyu
and
connected to DONET (
Figure 2b,c
). The pore pressure data
obtained show that the plate boundary fault slips slowly
(by 1–2 cm) over a duration of ~2 weeks, with a frequency
of every 1 to 1.5 years, in the shallow part of the presumed
earthquake fault (Araki et al., 2017). Because recent seis
-
mological studies reveal a possible relationship between
slow slip phenomena and the timing of large earthquakes
(e.g., Araki et al., 2017), the development of a seafloor net
-
work for real-time geodetic observations that includes a
borehole observatory, seafloor tiltmeters, and fiber-optic
cable strainmeters is underway to quickly identify unusual
slip behavior (Aoi et al., 2020).
After the 2011 Tōhoku-Oki earthquake, the National
Research Institute for Earth Science and Disaster
Resilience (NIED) quickly established an earthquake
and tsunami monitoring network called S-net to moni-
tor aftershock activity and to detect future tsunamis for
early warning purposes (
Figure 3b
, e.g., Mulia and Satake,
2021). S-net is characterized by seismometers and pres-
sure gauges embedded in offshore submarine cables
that are now used to develop and implement a tsunami
inundation early warning system. In the western part of
the Nankai Trough, a hybrid observation network called
N-net is under construction, with the features of both
S-net (i.e., cable-
embedded sensor system) and DONET
(i.e., node-
connected sensor system).
a
b
FIGURE 3. (a) Distribution of DONET observatories with landing sta-
tions along the Nankai Trough. (b) Distribution of S-net earthquake
and tsunami monitoring observatories along the Japan Trench. S-net
includes seismometers and pressure gauges embedded in offshore
submarine cables.
After Aoi et al. (2020), Figure 6 (a) and Figure 4 (b)
Similar to the Nankai Trough but on the other side of
the Pacific Ocean, the Cascadia Subduction Zone (CSZ),
runs beneath the west coast of the United States from
northern California up through Washington state and then
into southern Canada beneath Vancouver Island. Ocean
Networks Canada (ONC) installed seafloor cabled obser
-
vatories, called NEPTUNE and VENUS, to measure seafloor
tectonic movement on the CSZ where the Juan de Fuca
Plate subducts beneath the North American Plate. In 1700,
the CSZ ruptured in a large M9 earthquake and produced
tsunamis both locally and across the ocean in Japan, so we
know the CSZ represents a significant earthquake and tsu
-
nami hazard to Canada and the United States. ONC’s seabed
geodesy observatory uses long-endurance acoustic sens-
ing seafloor monument nodes, similar to Japan’s DONET,
where the data are wirelessly transmitted to a surface
autonomous vehicle that, in turn, connects with the Global
Navigation Satellite System (GNSS) (
Figure 4
; Farrugia et al.,
2019). Knowledge of the relative distance between the
nodes enables scientists to calculate movement between
the two converging plates with high accuracy.
To date, most seafloor cabled observatories and other
infrastructure designed to make tsunami early warning
a possibility are located in the Pacific Ocean. The vari
-
ety of earthquake and tsunami-generating sources in
72
the Caribbean dictate the location and instrument types
needed for an ocean monitoring network in this region. An
extensive network of coastal sea level stations, DART tsu-
nameters, GNSS stations, and seismic stations contribute
real-time data to ICG/CARIBE-EWS. These data are used
by the Pacific Tsunami Warning Center, as the Regional
Tsunami Service Provider, and national tsunami warning
centers to monitor, detect, and warn of impending tsuna-
mis (von Hillebrandt-Andrade, 2013).
UNESCO performance standards are carefully applied
to the location of Caribbean seismic stations with the
goal of reducing to within one minute the time needed to
detect an earthquake and determine whether it reaches
a magnitude threshold of M4.5, which could generate
strong enough shaking to constitute a tsunami threat
(e.g., McNamara et al., 2016). In the first 10 years of
ICG/CARIBE-EWS (2006–2015), large increases in the num-
ber of data-sharing seismic and sea level stations improved
the performance of seismic and tsunami wave detection
(
Figure 5
). For example, the seismic system increased from
10 stations, mostly operated by the onshore Puerto Rico
Seismic Network (PRSN), to over 100 stations shared by
all countries in the region (McNamara et al.,
2016). The
number of sea level stations reporting in near-real time
increased from 5 to 78 between 2004 and August 2017
(
http://caribewave.org
). However, station operation faces
many challenges in a region with annual hurricanes and
other hazards. In September 2017, earthquake and tsu-
nami monitoring performance in the Caribbean was sig-
nificantly reduced due to damage to onshore networks
and regional seismic and sea level networks by Hurricanes
Maria and Irma, and then Hurricane Iota in 2020 (
Figure 5
).
Other regional and international partners lost numer-
ous pieces of equipment and data transmission capabilities
due to wind and water damage. In addition, the COVID-19
pandemic has degraded performance, as all fieldwork to
repair and maintain stations came to a halt, which resulted
in long-term data drops. Today, station visits are beginning
to occur as COVID travel restrictions are lifted throughout
the region. Critically, based on the experience from the
recent hurricanes, many instrumentation sites were not
only repaired but also hardened to improve data conti-
nuity during future meteorological events. Although field
FIGURE 4. This map of Ocean Networks Canada (ONC) networks high-
lights the geographical distribution of community observatories (blue
diamonds) and community partnerships (red triangles). Community
observatories include an ocean-bottom instrument platform that is
linked to a cable through a wharf connection and provides continu-
ous, real-time monitoring in bays and estuaries along Canada’s three
coasts. The inset map shows the two major seafloor cabled observato-
ries, NEPTUNE and VENUS, operated by ONC. NEPTUNE and VENUS
monitor the Cascadia Subduction Zone and the British Columbia
coastline, respectively. Each branch of the cable (solid blue lines) is
connected to a node (orange squares), which provides power and
high-bandwidth Internet connections to all sensors. Other instrumen-
tation such as current and wave radars are identified in the legend.
Community Observatory
Community Partnership
Node
Ocean Radar
Wave Radar (WERA) Range
Fiber-Optic Cable
Ferry Route
FIGURE 5. Evolution of sea level stations in the Caribbean and adjacent regions
available in near-real time for the Intergovernmental Coordination Group for
the Tsunami and Other Coastal Hazards Warning System for the Caribbean and
Adjacent Regions (ICG/CARIBE-EWS) along with major events and programs
that have affected data availability (blue line). The CPACC (Caribbean Planning
for Adaptation to Global Climate Change) and MACC (Mainstreaming Adaptation
to Climate Change) were two programs of the Caribbean Community Center for
Climate Change that included installation of coastal gauges. Hurricanes Irma
and Maria in 2017 and the COVID-19 pandemic and Hurricane Iota in 2020 have
deeply impacted growth projections. The upswing of coastal gauges is noted
after the Indian Ocean Tsunami (2004).
Year
1960
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1978
1980
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1986
1988
1990
1992
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1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
2018
2020
2022
2024
100
80
60
40
20
0
ICG/CARIBE-EWS SEA LEVEL STATIONS TREND IN THE CARIBBEAN
CPACC
Indian Ocean
Tsunami
Hurricanes
Irma and Maria
COVID-19 Pandemic
and Hurricane Iota
MACC
Number of Stations Sharing
Data in Real Time
73