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The 2016 Fukushima earthquake and tsunami: Local tsunami behavior and recommendations for tsunami disaster risk reduction
International Journal of Disaster Risk Reduction 21 (2017) 323–330
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International Journal of Disaster Risk Reduction journal homepage: www.elsevier.com/locate/ijdrr
The 2016 Fukushima earthquake and tsunami: Local tsunami behavior and recommendations for tsunami disaster risk reduction
MARK
⁎
Anawat Suppasria, , Natt Leelawata, Panon Latcharotea, Volker Roebera, Kei Yamashitaa, Akihiro Hayashia, Hiroyuki Ohirab, Kentaro Fukuic, Akifumi Hisamatsub, David Nguyenb, Fumihiko Imamuraa a b c
International Research Institute of Disaster Science (IRIDeS), Tohoku University, Japan Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University, Japan Department of Civil Engineering and Architecture, School of Engineering, Tohoku University, Japan
A R T I C L E I N F O
A BS T RAC T
Keywords: 2016 Fukushima earthquake and tsunami Tsunami disaster risk reduction Tsunami mechanism Tsunami runup Tsunami warning
The 2016 Fukushima earthquake and tsunami presented several new issues of tsunami generation mechanism and propagation, as well as of organizational responses such as evacuation procedures and dissemination of tsunami warning. This study focuses on explanations to issues of public interest based on the experiences during the 2016 tsunami: (1) Despite Fukushima Prefecture's proximity to the earthquake's epicenter, why was the largest wave observed in the neighboring Miyagi Prefecture? (2) Why was the second wave of the tsunami larger than the first? (3) Why was the tsunami advisory elevated to a tsunami warning in Miyagi Prefecture? (4) Why did tsunami intrusions into rivers occur? (5) And why were local tsunami runup values much higher than the broadcasted tsunami amplitudes from local tide gauges? In the wake of the 2011 Great East Japan earthquake and tsunami, this study also points out remaining problems and new perspectives related to tsunami disaster risk reduction. These include tsunami warnings and advisories by emergency management agencies, the fact that tsunami waves are higher near the coast than in the open ocean, and refraining from being close to rivers in case of a tsunami. Based to Japan's experiences with disaster mitigation, lessons were learned from numerous events that could lead to revisions and improvements of current warning systems and provide useful guidelines for other countries.
1. Introduction On 22nd November 2016 at 05:59 JST (UTC+09:00), a large earthquake occurred off the east coast of Japan, near Fukushima Prefecture. The magnitude of this normal-fault earthquake was recorded at Mj 7.4 (from the originally announced Mj 7.3) by the Japan Meteorological Agency (JMA) at a depth of 25 km (from the originally announced 10 km) [1]. Meanwhile, Mw 6.9 at depth 11 km was given by the United States Geological Survey (USGS) [2]. The shock had a maximum seismic intensity of “5-” in Japanese “Shindo” scale which corresponds to VII on the Mercalli scale [1]. Based on JMA data, as of 07:30 JST, further seismic activity was recorded, which include one instance of categorized Shindo 5-, three instances measured at Shindo 3, seven of Shindo 2, and seven of Shindo 1 [1]. JMA stated this seismic event was an aftershock of the 2011 Great East Japan Earthquake [1]. According to Table 1, the JMA issued its first Tsunami Warnings/
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Advisories at 06:02 JST. This message contained tsunami warnings for Fukushima Prefecture and Tsunami Advisories for the Pacific coastlines of Aomori Prefecture, Iwate Prefecture, Miyagi Prefecture, Ibaraki Prefecture, and Kujukuri and Sotobo area in Chiba Prefecture. By 07:26 JST, the Tsunami Advisories included the Uchibo Area of Chiba Prefecture and Izu Islands. At 08:09 JST, Miyagi Prefecture were elevated to a Tsunami Warning. At 09:46 JST, the Tsunami Warnings were downgraded to Tsunami Advisories which covered Iwate Prefecture, Miyagi Prefecture, Fukushima Prefecture, and Ibaraki Prefecture. Finally, the JMA lifted all Tsunami Warnings and Advisories at 12:50 JST. As the maximum tsunami amplitude of 1.4 m was measured at Sendai port, this was the highest tsunami event since 2011. This article provides preliminary findings of the aforementioned issues that should be further investigated in future studies. Although this earthquake and tsunami event only caused minor damages with no human casualty, there are some remaining and new issues for tsunami
Corresponding author. International Research Institute of Disaster Science (IRIDeS), Tohoku University, Aoba, Aramaki-Aza, Aoba 468-1, Sendai 980-0845, Japan. E-mail address: [email protected] (A. Suppasri).
http://dx.doi.org/10.1016/j.ijdrr.2016.12.016 Received 20 December 2016; Accepted 27 December 2016 Available online 17 January 2017 2212-4209/ © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
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Table 1 Tsunami warnings and advisories. (For interpretation of the references to color in this table, the reader is referred to the web version of this article.). Source [1].
*Note: Red indicates tsunami warning. Yellow indicates tsunami advisory.
The orientation of the two nodal planes obtained from USGS (2016) (Fig. 2) were used for our preliminary computed initial sea surface elevation [6] based on a scaling empirical formula [7] and distribution of aftershocks [8]. Another extraordinary issue for this earthquake was that the fault size estimated by the mentioned scaling empirical formula is rather large with smaller slip (fault size =39×17 km2 and slip =1.4 m) as shown in Fig. 2(a) but smaller fault size with larger slip based on the distribution of aftershocks (fault size =20×10 km2 and slip =4.0 m from [8] as shown in Fig. 2(b).
disaster risk reduction perspectives that should be pointed out and correctly understood before the next tsunami event as summarized in the following section. 2. Emerging tsunami related issues This section discusses five issues of public interest related to this tsunami event. First, while the epicenter of the earthquake was close to Fukushima Prefecture, the highest tsunami wave was recorded in Sendai Port, located further north in Miyagi Prefecture. Second, the second wave, rather than the first, was the highest wave. Third, the tsunami advisory was upgraded to a tsunami warning in Miyagi Prefecture. Fourth, the local tsunami runup was observed to be higher than the observed tsunami amplitude at the tide gauge in Sendai Port. Finally, the tsunami propagated into rivers as undular bores.
Table 2 Observed maximum tsunami amplitude along the east coast of Japan. Source [1]. Location
2.1. The highest observed tsunami was in Sendai, Miyagi Prefecture rather than near the earthquake's epicenter, off Fukushima Prefecture The maximum tsunami amplitudes observed at tide gauge stations along the east coast of Japan showed that the maximum tsunami amplitude of 1.4 m was observed at Sendai Port in Miyagi Prefecture while the maximum observed tsunami amplitude in Fukushima Prefecture was only 0.9 m as shown in Table 2 [1]. This is due to the fact that despite the epicenter being near Fukushima, its fault plane (strike angle) was perpendicular to Sendai, while parallel to other areas in Fukushima. The strike angles of two nodal planes (45–60 and 220– 232) from all well-known sources of fault mechanism are similar [1–5]. In other words, the tsunami wave energy was spread directly towards coastal areas near Sendai including wave refraction into Sendai bay. (Fig. 1).
Time (JST)
Iwate Prefecture
Kuji port Miyako Kamaishi Ofunato
0.8 0.4 0.2 0.4
07:54 08:09 08:58 07:56
Miyagi Prefecture
Ayukawa Ishinomaki port Sendai port
0.8 0.8 1.4
07:39 08:11 08:03
Fukushima Prefecture
Soma Onahama
0.8 0.9
07:54 07:06
Ibaraki Prefecture
Oarai Kashima port
0.6 0.5
06:49 07:08
Chiba Prefecture
Okitsu Mera Yaene
0.3 0.3 0.3
09:06 09:03 07:13
Tokyo
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Amplitude (m)
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Fig. 1. Location map, epicenter, location discussed in the paper.
should examine this kind of wave amplification. In addition, wave shoaling, refraction, and dispersive effects should also be considered inside Sendai bay.
Another issue that was discovered is related to the fault size and slip of this event is the earthquake magnitude. JMA finally announced Mj 7.4 (equal to Mw 7.2 based on [9] while estimation from other international sources [2,4,5] was Mw 6.9. The equivalent fault sizes and slips for these two different magnitude are 39×17 km2 and 1.4 m for Mw 6.9 whereas 55×21 km2 and 2.3 m for Mw 7.2. Such small difference of 0.3 Mw can cause significant result of the predicted tsunami height in case of small to moderate tsunami like this event which is related to tsunami warning system.
2.3. Tsunami threat level was elevated from “advisory” to “warning” in Miyagi Prefecture First, it is necessary to understand the current classification of the tsunami warnings and advisories utilized in Japan. JMA is an official agency that monitors and issues warning messages for all natural disasters including tsunamis [12]. Due to the experiences with the 2011 Great East Japan Earthquake and Tsunami, the terminology and classification of warnings in Japan were modified [13–15]. Table 3 shows the current warning classification and description of tsunami criterion [15,16]. In order to limit complications, a wider range has been applied to this classification system. When a tsunami with the height ranging from 20 cm to 1 m is expected, a tsunami advisory is issued (indicated by a yellow color; advisory). When a tsunami is expected to be between 1 m and 3 m, a tsunami warning is issued (indicated by a red color; warning). If a tsunami is expected to be greater than 3 m, a major tsunami warning is issued (indicated by a purple color; emergency warning). At the beginning, JMA expected the arrival of the tsunami wave in Fukushima Prefecture to be higher than 1 m; therefore a tsunami warning was issued for that prefecture. At 08:09 JST due to the observed 1.4 m tsunami height at Sendai Port, the tsunami advisory of Miyagi Prefecture had to be elevated to a tsunami warning (over 1– 3 m).
2.2. The second wave was the largest It is commonly understood for ordinary persons in Japan that the first wave of a tsunami is the largest wave while many tsunamis showed the second or third wave to be the highest [10]. However, the second wave observed at Sendai Port was the largest wave as shown in Fig. 3. In addition to the fault orientation, which focused the tsunami into Sendai Bay, wave reflection and refraction were other contributors. Sendai Bay (Fig. 4) is a very shallow (average water depth is less than 50 m) and wide bay. Due to this coastal topography, the waves are amplified due to wave shoaling and refraction inside the bay. Also, superposition of the incoming and reflected waves from the Fukushima coast played a role. As shown in Fig. 4, the first wave crest (red) hit Fukushima Prefecture (after 20 min) and reflected from the steep coast (another 20 min later). The first wave trough (blue) hit Sendai Port after 60 min and the first wave crest arrived at Sendai Port after 80 min. The reflected wave from Fukushima approached Sendai Port after 100 min and superimposed with the second incoming waves after 120 min. Another explanation for the unexpectedly high tsunami wave inside Sendai Bay might be connected to the wave resonance with the fundamental oscillation mode. The amplification of a tsunami wave inside a bay is highly dependent on the tsunami wavelength, which can excite the natural oscillation inside the bay. Therefore, further research
2.4. Local tsunami runup was higher than the observed tsunami amplitude from tide gauge at Sendai port In general, the tsunami height can be amplified or enlarged up to 2– 4 times during the runup process. Based on our preliminary survey, 325
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Fig. 2. Orientation of two fault planes based on USGS [2] and our computed initial sea surface elevation based on a scaling empirical formula (a) (fault size =39×17 km2 and slip =1.4 m) and distribution of aftershocks (b) (fault size =20×10 km2 and slip =4.0 m).
2.5. Tsunami intrusion into rivers
tsunami runup higher than the observed tsunami wave amplitude of 1.4 m at Sendai Port was measured at several sites. In the Miyato area of Higashi-Matsushima City in Miyagi Prefecture, tsunami runup heights of more than 2–3 m were found caused by nearshore processes over the coastal topography. For example, in Ohama fishing port, a runup higher than 3 m was measured at an inclined driveway of a resident's house as shown in Fig. 5. The reasons for such high runup are (1) the shape of the port trapping the first wave before the arrival of the second wave, (2) the tsunami occurred during a flood-tide stage that help pushing the wave inside the port and (3) the existing gentle sloop that assisted wave runup.
In addition to issues regarding tsunami propagation offshore and inundation on land, tsunami intrusion into rivers were also observed. This phenomenon was clearly observed at Sunaoshi River in Tagajo City, where the tsunami propagated over 3 km into the river [17]. The tsunami speed is estimated to be about 14 km/s and the maximum rising of the river level reached 0.9 m (0.6–0.7 m above the normal level) [17]. This phenomenon was filmed by many eyewitnesses and interested many local residents. In the case of the 2011 tsunami, the river tsunami overflew the embankment of the Sunaoshi River with more than 2 m of inundation depth that led to damages along many areas along the river [18].
Fig. 3. Observed tsunami waveform at Sendai port [11].
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Fig. 4. Tsunami propagation from Fukushima to Sendai Bay [6].
3. New and remaining perspectives towards disaster risk reduction (DRR)
Table 3 Current Tsunami Warnings and Advisories Classification in Japan. Source: JMA [16]. Estimated tsunami height
Warning classification
Tsunami warning classification
10 m < h 5 m < h≤10 m 3 m < h≤5 m 1 m < h≤3 m 0.2 m≤h≤1 m h < 0.2 m
Emergency warning Emergency warning Emergency warning Warning Advisory Forecast
Major tsunami warning Major tsunami warning Major tsunami warning Tsunami warning Tsunami warning Tsunami forecast
3.1. Wait for the official cancellation of a tsunami warning Until now, it is still difficult to include all possible earthquake fault mechanisms and high-resolution coastal topography in a tsunami warning system database. Furthermore, it should not be assumed that the highest tsunami wave will strike a location nearest to the earthquake's epicenter, nor should the first wave expected to be the tallest. People are advised to evacuate to a safe place inland or to higher ground, and not to return to a coastal area until the official tsunami warning is cancelled.
Note: h denotes Height (sea level changes in m).
3.2. Tsunami warning and broadcasting As the responses to the warnings depend on the way that the message is interpreted and understood, it is necessary to focus on the issues related to the warnings and broadcasting of this event. We can
Fig. 5. Tsunami runup T.P. +4.1 m (yellow dashed line) and inundation height T.P. +3.6 m (blue dashed line) at Ohama fishing port, Miyato area of Higashi-Matsushima city, Miyagi Prefecture. The runup and inundation heights were measured with a laser range finder, staff, and Promark GPS device. The picture was provided by Miyagi Prefecture Fisheries Cooperative Association (JF Miyagi) Miyato western branch. (Picture taken date: 22/11/2016). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 6. Breaking news broadcasted on NHK World on November 22, 2016. Note: Source: [21].
this disaster event. Moreover, Social Networking Services (SNS) played an important role during this tsunami event. For example, SNS was used to confirm people's safety. Facebook provided the Facebook Safety Check, which covered a far-reaching area that even included Tokyo [23]. Another example was Twitter, which was used to retweet disaster information. Some people shared their recorded videos showing the river tsunamis in some areas.
see significant changes in the warning system, especially the broadcasting process, compared to those utilized in the 2011 Great East Japan Tsunami. Broadcasting warning messages through television, radio, and speakers only in areas expected to be affected, as done in 2011, lead to insufficient results due to blackouts and the loss of personnel and broadcasting vehicles in the tsunami [19]. NHK is Japan's national public broadcasting organization, with NHK World representing their international broadcasting service. NHK World broadcasted news of the 2016 earthquake and tsunami in English from the beginning of the event. The reporters used English language for all programs of NHK World. The news ticker was updated over nearly the entire period. During this news coverage, some realtime breaking news, such as press releases from JMA, were simultaneously interpreted from Japanese to English. Fig. 6 shows the screenshot of an NHK World broadcast on the day of the event. In contrast to the calm voice used during the 2011 tsunami, terms such as “Evacuate immediately!”, “Tsunami! Evacuate!”, etc. were used to warn people to evacuate from locations expected to be hit by the tsunami. Also, some phases such as “Please remember the Great East Japan Earthquake and move to higher ground”, were used to remind the audience of the 2011 devastation [20]. The warnings were also released in Chinese and Korean languages [19]. In addition, Japanese Prime Minister Shinzo Abe included the following message in his opening statement during his visit to Argentina, which was broadcasted live.
3.3. Local tsunami on land can be higher than the observed tsunami at sea In general, many people do not understand the difference between the two types of tsunami measurements, (1) tsunami wave amplitude measured at a tide station and (2) tsunami runup measured on land. These two types of measurements should not be confused or directly compared because their definitions are different. Nevertheless, this can be a lesson as the tsunami runup is higher than the observed tsunami amplitude. Therefore, people should keep this fact in mind and should act or evacuate accordingly. The maximum observed wave amplitude announced during a tsunami warning is not equal to the maximum wave runup. Often, as in the case of this event, the maximum wave runup is much higher than the observations at local tide level. It is also important to emphasize on the point that a tsunami is nothing to play with. Beachgoers, hobby fishermen, and surfers are advised to follow instructions from emergency managers and local authorities and stay off beaches until the “all clear” sign is given. Tsunami waves should not be confused with regular swell waves. Tsunamis are not surfable waves because they do not break like regular swell waves. In contrast, tsunamis behave like quickly-rising extreme tides and the water is often laden with debris. Attempts to surf tsunamis quickly end deadly.
“Just now a strong earthquake struck off the coast of Fukushima Prefecture and a tsunami warning was issued. I gave instructions to the relevant authorities to provide the public with information regarding tsunamis and evacuation in a timely and accurate manner, swiftly grasp the damage situation, and make all-out efforts toward emergency measures in response to the disaster. To reinforce this, I also directly instructed the Chief Cabinet Secretary to take all possible measures. …” [22]
3.4. Do not get close to a river tsunami
His statement directed people's focus to the event as well as it supported residents to continue following the information related to
As mentioned in sub-section 3.2, some people tried to get close to 328
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rivers to film the tsunami. Although, it was fortunate that the river tsunami did not lead to overtopping of the embankment, it nevertheless highlights the risk people can expose themselves to. Future tsunamis may not only overtop and destroy the river embankment as seen in 2011, but could also cause human casualties and property damage. Thus, no matter what tsunami size is expected, people should stay clear of rivers.
Association (JF Miyagi) Miyato western branch for their information on the tsunami trace in Ohama fishing port, Miyato Island and all other members of the Tsunami Engineering Laboratory, IRIDeS, Tohoku University for their cooperation during an emergency response of this tsunami event. This research was funded by Willis Research Network (WRN), Tokio Marine & Nichido Fire Insurance Co., Ltd. and the internal budget of IRIDeS (Hazards and Damage Evaluation and Mitigation unit), Tohoku University. Volker Roeber is greatly appreciating the support from the Japan Society for the Promotion of Science (JSPS), KAKENHI Grant Number 15K06224 (Tohoku University).
4. Conclusions Following the Sendai Framework for Disaster Risk Reduction 2015–2030 [24], in order to reduce risk, it is important for people to understand and to be prepared for disasters. This paper provides an explanation of the significant issues related to the 2016 Fukushima Earthquake and Tsunami. It was an event, which highlighted many interesting characteristics of the tsunami itself for future research and also illustrated the responses from Japanese authorities, which learned their lessons from the 2011 Great East Japan Tsunami. In addition to these explanations, some instructions are suggested in this paper. People should wait until the official cancellation is announced before returning to areas under tsunami threat. It is possible that the biggest wave will not necessary be the first wave. This paper gives a clear understanding of tsunami wave amplitude measurements and tsunami runup measurements. While the announced tsunami wave amplitude is small, the runup at the coastal area can be higher and more powerful. The tsunami warning database has still limitations related to the fault mechanisms, location, and detailed geography. Therefore, changes in the categorization of warnings should be expected depending on real time tsunami observations. While many countries focus on warning system development [25,26], it is still important to look into how these messages are disseminated. The lessons learned from the broadcasting of the warnings for the 2011 Great East Japan Tsunami led to changes in broadcasting methods. More insistent terms were used instead of the previously used softer and calmer tones. Using terms related to the 2011 tsunami invoked a sense of urgency to evacuate as they still reminded people of the devastation from the 2011 event. Nevertheless, as Gyoba [27] found that people outside the damage zone tend to overestimate tsunami heights whereas people within that area tend to underestimate the heights when receiving tsunami-warning messages. It is therefore necessary to clarify the information for the people to help them better understand the correct criteria of the warning categories. Further research should be conducted that takes into consideration the response of receivers, especially people outside the affected areas, in order to reduce the “cry-wolf” syndrome [28]. Another serious issue is people's difficulty in decision-making due to controversial evacuation suggestions. In 2011, the local authorities (e.g., village, town, or municipal administrative levels) within the same prefecture were responsible to provide evacuation information to their residents. As a result, some individuals who moved from a town or city to another during that period were confronted with various announcements [29]. This issue raised attention towards revising the evacuation guideline in the future. Lastly, tsunamis are one of the most dangerous natural hazards which can cause harm to people and properties. Traveling to expected tsunami arrival areas with the intent to record videos and take photographs, presents numerous risks to people's safety. We thus advise people to go to their designated evacuation shelter and/or stay off the affected area. It is also recommended to limit outdoor and communication activities to the minimum so that the local infrastructure and telecommunication systems can be used for emergency response.
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International Journal of Disaster Risk Reduction journal homepage: www.elsevier.com/locate/ijdrr
The 2016 Fukushima earthquake and tsunami: Local tsunami behavior and recommendations for tsunami disaster risk reduction
MARK
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Anawat Suppasria, , Natt Leelawata, Panon Latcharotea, Volker Roebera, Kei Yamashitaa, Akihiro Hayashia, Hiroyuki Ohirab, Kentaro Fukuic, Akifumi Hisamatsub, David Nguyenb, Fumihiko Imamuraa a b c
International Research Institute of Disaster Science (IRIDeS), Tohoku University, Japan Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University, Japan Department of Civil Engineering and Architecture, School of Engineering, Tohoku University, Japan
A R T I C L E I N F O
A BS T RAC T
Keywords: 2016 Fukushima earthquake and tsunami Tsunami disaster risk reduction Tsunami mechanism Tsunami runup Tsunami warning
The 2016 Fukushima earthquake and tsunami presented several new issues of tsunami generation mechanism and propagation, as well as of organizational responses such as evacuation procedures and dissemination of tsunami warning. This study focuses on explanations to issues of public interest based on the experiences during the 2016 tsunami: (1) Despite Fukushima Prefecture's proximity to the earthquake's epicenter, why was the largest wave observed in the neighboring Miyagi Prefecture? (2) Why was the second wave of the tsunami larger than the first? (3) Why was the tsunami advisory elevated to a tsunami warning in Miyagi Prefecture? (4) Why did tsunami intrusions into rivers occur? (5) And why were local tsunami runup values much higher than the broadcasted tsunami amplitudes from local tide gauges? In the wake of the 2011 Great East Japan earthquake and tsunami, this study also points out remaining problems and new perspectives related to tsunami disaster risk reduction. These include tsunami warnings and advisories by emergency management agencies, the fact that tsunami waves are higher near the coast than in the open ocean, and refraining from being close to rivers in case of a tsunami. Based to Japan's experiences with disaster mitigation, lessons were learned from numerous events that could lead to revisions and improvements of current warning systems and provide useful guidelines for other countries.
1. Introduction On 22nd November 2016 at 05:59 JST (UTC+09:00), a large earthquake occurred off the east coast of Japan, near Fukushima Prefecture. The magnitude of this normal-fault earthquake was recorded at Mj 7.4 (from the originally announced Mj 7.3) by the Japan Meteorological Agency (JMA) at a depth of 25 km (from the originally announced 10 km) [1]. Meanwhile, Mw 6.9 at depth 11 km was given by the United States Geological Survey (USGS) [2]. The shock had a maximum seismic intensity of “5-” in Japanese “Shindo” scale which corresponds to VII on the Mercalli scale [1]. Based on JMA data, as of 07:30 JST, further seismic activity was recorded, which include one instance of categorized Shindo 5-, three instances measured at Shindo 3, seven of Shindo 2, and seven of Shindo 1 [1]. JMA stated this seismic event was an aftershock of the 2011 Great East Japan Earthquake [1]. According to Table 1, the JMA issued its first Tsunami Warnings/
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Advisories at 06:02 JST. This message contained tsunami warnings for Fukushima Prefecture and Tsunami Advisories for the Pacific coastlines of Aomori Prefecture, Iwate Prefecture, Miyagi Prefecture, Ibaraki Prefecture, and Kujukuri and Sotobo area in Chiba Prefecture. By 07:26 JST, the Tsunami Advisories included the Uchibo Area of Chiba Prefecture and Izu Islands. At 08:09 JST, Miyagi Prefecture were elevated to a Tsunami Warning. At 09:46 JST, the Tsunami Warnings were downgraded to Tsunami Advisories which covered Iwate Prefecture, Miyagi Prefecture, Fukushima Prefecture, and Ibaraki Prefecture. Finally, the JMA lifted all Tsunami Warnings and Advisories at 12:50 JST. As the maximum tsunami amplitude of 1.4 m was measured at Sendai port, this was the highest tsunami event since 2011. This article provides preliminary findings of the aforementioned issues that should be further investigated in future studies. Although this earthquake and tsunami event only caused minor damages with no human casualty, there are some remaining and new issues for tsunami
Corresponding author. International Research Institute of Disaster Science (IRIDeS), Tohoku University, Aoba, Aramaki-Aza, Aoba 468-1, Sendai 980-0845, Japan. E-mail address: [email protected] (A. Suppasri).
http://dx.doi.org/10.1016/j.ijdrr.2016.12.016 Received 20 December 2016; Accepted 27 December 2016 Available online 17 January 2017 2212-4209/ © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
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Table 1 Tsunami warnings and advisories. (For interpretation of the references to color in this table, the reader is referred to the web version of this article.). Source [1].
*Note: Red indicates tsunami warning. Yellow indicates tsunami advisory.
The orientation of the two nodal planes obtained from USGS (2016) (Fig. 2) were used for our preliminary computed initial sea surface elevation [6] based on a scaling empirical formula [7] and distribution of aftershocks [8]. Another extraordinary issue for this earthquake was that the fault size estimated by the mentioned scaling empirical formula is rather large with smaller slip (fault size =39×17 km2 and slip =1.4 m) as shown in Fig. 2(a) but smaller fault size with larger slip based on the distribution of aftershocks (fault size =20×10 km2 and slip =4.0 m from [8] as shown in Fig. 2(b).
disaster risk reduction perspectives that should be pointed out and correctly understood before the next tsunami event as summarized in the following section. 2. Emerging tsunami related issues This section discusses five issues of public interest related to this tsunami event. First, while the epicenter of the earthquake was close to Fukushima Prefecture, the highest tsunami wave was recorded in Sendai Port, located further north in Miyagi Prefecture. Second, the second wave, rather than the first, was the highest wave. Third, the tsunami advisory was upgraded to a tsunami warning in Miyagi Prefecture. Fourth, the local tsunami runup was observed to be higher than the observed tsunami amplitude at the tide gauge in Sendai Port. Finally, the tsunami propagated into rivers as undular bores.
Table 2 Observed maximum tsunami amplitude along the east coast of Japan. Source [1]. Location
2.1. The highest observed tsunami was in Sendai, Miyagi Prefecture rather than near the earthquake's epicenter, off Fukushima Prefecture The maximum tsunami amplitudes observed at tide gauge stations along the east coast of Japan showed that the maximum tsunami amplitude of 1.4 m was observed at Sendai Port in Miyagi Prefecture while the maximum observed tsunami amplitude in Fukushima Prefecture was only 0.9 m as shown in Table 2 [1]. This is due to the fact that despite the epicenter being near Fukushima, its fault plane (strike angle) was perpendicular to Sendai, while parallel to other areas in Fukushima. The strike angles of two nodal planes (45–60 and 220– 232) from all well-known sources of fault mechanism are similar [1–5]. In other words, the tsunami wave energy was spread directly towards coastal areas near Sendai including wave refraction into Sendai bay. (Fig. 1).
Time (JST)
Iwate Prefecture
Kuji port Miyako Kamaishi Ofunato
0.8 0.4 0.2 0.4
07:54 08:09 08:58 07:56
Miyagi Prefecture
Ayukawa Ishinomaki port Sendai port
0.8 0.8 1.4
07:39 08:11 08:03
Fukushima Prefecture
Soma Onahama
0.8 0.9
07:54 07:06
Ibaraki Prefecture
Oarai Kashima port
0.6 0.5
06:49 07:08
Chiba Prefecture
Okitsu Mera Yaene
0.3 0.3 0.3
09:06 09:03 07:13
Tokyo
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Amplitude (m)
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Fig. 1. Location map, epicenter, location discussed in the paper.
should examine this kind of wave amplification. In addition, wave shoaling, refraction, and dispersive effects should also be considered inside Sendai bay.
Another issue that was discovered is related to the fault size and slip of this event is the earthquake magnitude. JMA finally announced Mj 7.4 (equal to Mw 7.2 based on [9] while estimation from other international sources [2,4,5] was Mw 6.9. The equivalent fault sizes and slips for these two different magnitude are 39×17 km2 and 1.4 m for Mw 6.9 whereas 55×21 km2 and 2.3 m for Mw 7.2. Such small difference of 0.3 Mw can cause significant result of the predicted tsunami height in case of small to moderate tsunami like this event which is related to tsunami warning system.
2.3. Tsunami threat level was elevated from “advisory” to “warning” in Miyagi Prefecture First, it is necessary to understand the current classification of the tsunami warnings and advisories utilized in Japan. JMA is an official agency that monitors and issues warning messages for all natural disasters including tsunamis [12]. Due to the experiences with the 2011 Great East Japan Earthquake and Tsunami, the terminology and classification of warnings in Japan were modified [13–15]. Table 3 shows the current warning classification and description of tsunami criterion [15,16]. In order to limit complications, a wider range has been applied to this classification system. When a tsunami with the height ranging from 20 cm to 1 m is expected, a tsunami advisory is issued (indicated by a yellow color; advisory). When a tsunami is expected to be between 1 m and 3 m, a tsunami warning is issued (indicated by a red color; warning). If a tsunami is expected to be greater than 3 m, a major tsunami warning is issued (indicated by a purple color; emergency warning). At the beginning, JMA expected the arrival of the tsunami wave in Fukushima Prefecture to be higher than 1 m; therefore a tsunami warning was issued for that prefecture. At 08:09 JST due to the observed 1.4 m tsunami height at Sendai Port, the tsunami advisory of Miyagi Prefecture had to be elevated to a tsunami warning (over 1– 3 m).
2.2. The second wave was the largest It is commonly understood for ordinary persons in Japan that the first wave of a tsunami is the largest wave while many tsunamis showed the second or third wave to be the highest [10]. However, the second wave observed at Sendai Port was the largest wave as shown in Fig. 3. In addition to the fault orientation, which focused the tsunami into Sendai Bay, wave reflection and refraction were other contributors. Sendai Bay (Fig. 4) is a very shallow (average water depth is less than 50 m) and wide bay. Due to this coastal topography, the waves are amplified due to wave shoaling and refraction inside the bay. Also, superposition of the incoming and reflected waves from the Fukushima coast played a role. As shown in Fig. 4, the first wave crest (red) hit Fukushima Prefecture (after 20 min) and reflected from the steep coast (another 20 min later). The first wave trough (blue) hit Sendai Port after 60 min and the first wave crest arrived at Sendai Port after 80 min. The reflected wave from Fukushima approached Sendai Port after 100 min and superimposed with the second incoming waves after 120 min. Another explanation for the unexpectedly high tsunami wave inside Sendai Bay might be connected to the wave resonance with the fundamental oscillation mode. The amplification of a tsunami wave inside a bay is highly dependent on the tsunami wavelength, which can excite the natural oscillation inside the bay. Therefore, further research
2.4. Local tsunami runup was higher than the observed tsunami amplitude from tide gauge at Sendai port In general, the tsunami height can be amplified or enlarged up to 2– 4 times during the runup process. Based on our preliminary survey, 325
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Fig. 2. Orientation of two fault planes based on USGS [2] and our computed initial sea surface elevation based on a scaling empirical formula (a) (fault size =39×17 km2 and slip =1.4 m) and distribution of aftershocks (b) (fault size =20×10 km2 and slip =4.0 m).
2.5. Tsunami intrusion into rivers
tsunami runup higher than the observed tsunami wave amplitude of 1.4 m at Sendai Port was measured at several sites. In the Miyato area of Higashi-Matsushima City in Miyagi Prefecture, tsunami runup heights of more than 2–3 m were found caused by nearshore processes over the coastal topography. For example, in Ohama fishing port, a runup higher than 3 m was measured at an inclined driveway of a resident's house as shown in Fig. 5. The reasons for such high runup are (1) the shape of the port trapping the first wave before the arrival of the second wave, (2) the tsunami occurred during a flood-tide stage that help pushing the wave inside the port and (3) the existing gentle sloop that assisted wave runup.
In addition to issues regarding tsunami propagation offshore and inundation on land, tsunami intrusion into rivers were also observed. This phenomenon was clearly observed at Sunaoshi River in Tagajo City, where the tsunami propagated over 3 km into the river [17]. The tsunami speed is estimated to be about 14 km/s and the maximum rising of the river level reached 0.9 m (0.6–0.7 m above the normal level) [17]. This phenomenon was filmed by many eyewitnesses and interested many local residents. In the case of the 2011 tsunami, the river tsunami overflew the embankment of the Sunaoshi River with more than 2 m of inundation depth that led to damages along many areas along the river [18].
Fig. 3. Observed tsunami waveform at Sendai port [11].
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Fig. 4. Tsunami propagation from Fukushima to Sendai Bay [6].
3. New and remaining perspectives towards disaster risk reduction (DRR)
Table 3 Current Tsunami Warnings and Advisories Classification in Japan. Source: JMA [16]. Estimated tsunami height
Warning classification
Tsunami warning classification
10 m < h 5 m < h≤10 m 3 m < h≤5 m 1 m < h≤3 m 0.2 m≤h≤1 m h < 0.2 m
Emergency warning Emergency warning Emergency warning Warning Advisory Forecast
Major tsunami warning Major tsunami warning Major tsunami warning Tsunami warning Tsunami warning Tsunami forecast
3.1. Wait for the official cancellation of a tsunami warning Until now, it is still difficult to include all possible earthquake fault mechanisms and high-resolution coastal topography in a tsunami warning system database. Furthermore, it should not be assumed that the highest tsunami wave will strike a location nearest to the earthquake's epicenter, nor should the first wave expected to be the tallest. People are advised to evacuate to a safe place inland or to higher ground, and not to return to a coastal area until the official tsunami warning is cancelled.
Note: h denotes Height (sea level changes in m).
3.2. Tsunami warning and broadcasting As the responses to the warnings depend on the way that the message is interpreted and understood, it is necessary to focus on the issues related to the warnings and broadcasting of this event. We can
Fig. 5. Tsunami runup T.P. +4.1 m (yellow dashed line) and inundation height T.P. +3.6 m (blue dashed line) at Ohama fishing port, Miyato area of Higashi-Matsushima city, Miyagi Prefecture. The runup and inundation heights were measured with a laser range finder, staff, and Promark GPS device. The picture was provided by Miyagi Prefecture Fisheries Cooperative Association (JF Miyagi) Miyato western branch. (Picture taken date: 22/11/2016). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Fig. 6. Breaking news broadcasted on NHK World on November 22, 2016. Note: Source: [21].
this disaster event. Moreover, Social Networking Services (SNS) played an important role during this tsunami event. For example, SNS was used to confirm people's safety. Facebook provided the Facebook Safety Check, which covered a far-reaching area that even included Tokyo [23]. Another example was Twitter, which was used to retweet disaster information. Some people shared their recorded videos showing the river tsunamis in some areas.
see significant changes in the warning system, especially the broadcasting process, compared to those utilized in the 2011 Great East Japan Tsunami. Broadcasting warning messages through television, radio, and speakers only in areas expected to be affected, as done in 2011, lead to insufficient results due to blackouts and the loss of personnel and broadcasting vehicles in the tsunami [19]. NHK is Japan's national public broadcasting organization, with NHK World representing their international broadcasting service. NHK World broadcasted news of the 2016 earthquake and tsunami in English from the beginning of the event. The reporters used English language for all programs of NHK World. The news ticker was updated over nearly the entire period. During this news coverage, some realtime breaking news, such as press releases from JMA, were simultaneously interpreted from Japanese to English. Fig. 6 shows the screenshot of an NHK World broadcast on the day of the event. In contrast to the calm voice used during the 2011 tsunami, terms such as “Evacuate immediately!”, “Tsunami! Evacuate!”, etc. were used to warn people to evacuate from locations expected to be hit by the tsunami. Also, some phases such as “Please remember the Great East Japan Earthquake and move to higher ground”, were used to remind the audience of the 2011 devastation [20]. The warnings were also released in Chinese and Korean languages [19]. In addition, Japanese Prime Minister Shinzo Abe included the following message in his opening statement during his visit to Argentina, which was broadcasted live.
3.3. Local tsunami on land can be higher than the observed tsunami at sea In general, many people do not understand the difference between the two types of tsunami measurements, (1) tsunami wave amplitude measured at a tide station and (2) tsunami runup measured on land. These two types of measurements should not be confused or directly compared because their definitions are different. Nevertheless, this can be a lesson as the tsunami runup is higher than the observed tsunami amplitude. Therefore, people should keep this fact in mind and should act or evacuate accordingly. The maximum observed wave amplitude announced during a tsunami warning is not equal to the maximum wave runup. Often, as in the case of this event, the maximum wave runup is much higher than the observations at local tide level. It is also important to emphasize on the point that a tsunami is nothing to play with. Beachgoers, hobby fishermen, and surfers are advised to follow instructions from emergency managers and local authorities and stay off beaches until the “all clear” sign is given. Tsunami waves should not be confused with regular swell waves. Tsunamis are not surfable waves because they do not break like regular swell waves. In contrast, tsunamis behave like quickly-rising extreme tides and the water is often laden with debris. Attempts to surf tsunamis quickly end deadly.
“Just now a strong earthquake struck off the coast of Fukushima Prefecture and a tsunami warning was issued. I gave instructions to the relevant authorities to provide the public with information regarding tsunamis and evacuation in a timely and accurate manner, swiftly grasp the damage situation, and make all-out efforts toward emergency measures in response to the disaster. To reinforce this, I also directly instructed the Chief Cabinet Secretary to take all possible measures. …” [22]
3.4. Do not get close to a river tsunami
His statement directed people's focus to the event as well as it supported residents to continue following the information related to
As mentioned in sub-section 3.2, some people tried to get close to 328
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rivers to film the tsunami. Although, it was fortunate that the river tsunami did not lead to overtopping of the embankment, it nevertheless highlights the risk people can expose themselves to. Future tsunamis may not only overtop and destroy the river embankment as seen in 2011, but could also cause human casualties and property damage. Thus, no matter what tsunami size is expected, people should stay clear of rivers.
Association (JF Miyagi) Miyato western branch for their information on the tsunami trace in Ohama fishing port, Miyato Island and all other members of the Tsunami Engineering Laboratory, IRIDeS, Tohoku University for their cooperation during an emergency response of this tsunami event. This research was funded by Willis Research Network (WRN), Tokio Marine & Nichido Fire Insurance Co., Ltd. and the internal budget of IRIDeS (Hazards and Damage Evaluation and Mitigation unit), Tohoku University. Volker Roeber is greatly appreciating the support from the Japan Society for the Promotion of Science (JSPS), KAKENHI Grant Number 15K06224 (Tohoku University).
4. Conclusions Following the Sendai Framework for Disaster Risk Reduction 2015–2030 [24], in order to reduce risk, it is important for people to understand and to be prepared for disasters. This paper provides an explanation of the significant issues related to the 2016 Fukushima Earthquake and Tsunami. It was an event, which highlighted many interesting characteristics of the tsunami itself for future research and also illustrated the responses from Japanese authorities, which learned their lessons from the 2011 Great East Japan Tsunami. In addition to these explanations, some instructions are suggested in this paper. People should wait until the official cancellation is announced before returning to areas under tsunami threat. It is possible that the biggest wave will not necessary be the first wave. This paper gives a clear understanding of tsunami wave amplitude measurements and tsunami runup measurements. While the announced tsunami wave amplitude is small, the runup at the coastal area can be higher and more powerful. The tsunami warning database has still limitations related to the fault mechanisms, location, and detailed geography. Therefore, changes in the categorization of warnings should be expected depending on real time tsunami observations. While many countries focus on warning system development [25,26], it is still important to look into how these messages are disseminated. The lessons learned from the broadcasting of the warnings for the 2011 Great East Japan Tsunami led to changes in broadcasting methods. More insistent terms were used instead of the previously used softer and calmer tones. Using terms related to the 2011 tsunami invoked a sense of urgency to evacuate as they still reminded people of the devastation from the 2011 event. Nevertheless, as Gyoba [27] found that people outside the damage zone tend to overestimate tsunami heights whereas people within that area tend to underestimate the heights when receiving tsunami-warning messages. It is therefore necessary to clarify the information for the people to help them better understand the correct criteria of the warning categories. Further research should be conducted that takes into consideration the response of receivers, especially people outside the affected areas, in order to reduce the “cry-wolf” syndrome [28]. Another serious issue is people's difficulty in decision-making due to controversial evacuation suggestions. In 2011, the local authorities (e.g., village, town, or municipal administrative levels) within the same prefecture were responsible to provide evacuation information to their residents. As a result, some individuals who moved from a town or city to another during that period were confronted with various announcements [29]. This issue raised attention towards revising the evacuation guideline in the future. Lastly, tsunamis are one of the most dangerous natural hazards which can cause harm to people and properties. Traveling to expected tsunami arrival areas with the intent to record videos and take photographs, presents numerous risks to people's safety. We thus advise people to go to their designated evacuation shelter and/or stay off the affected area. It is also recommended to limit outdoor and communication activities to the minimum so that the local infrastructure and telecommunication systems can be used for emergency response.
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Acknowledgments We would like to thank Miyagi Prefecture Fisheries Cooperative 329
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