International Journal of Disaster Risk Reduction 21 (2017) 323–330 Contents lists available at ScienceDirect International Journal of Disaster Risk Reduction journal homepage: www.elsevier.com/locate/ijdrr The 2016 Fukushima earthquake and tsunami: Local tsunami behavior and MARK recommendations for tsunami disaster risk reduction ⁎ Anawat Suppasria, , Natt Leelawata, Panon Latcharotea, Volker Roebera, Kei Yamashitaa, Akihiro Hayashia, Hiroyuki Ohirab, Kentaro Fukuic, Akifumi Hisamatsub, David Nguyenb, Fumihiko Imamuraa a International Research Institute of Disaster Science (IRIDeS), Tohoku University, Japan b Department of Civil and Environmental Engineering, Graduate School of Engineering, Tohoku University, Japan c Department of Civil Engineering and Architecture, School of Engineering, Tohoku University, Japan ARTICLE INFO ABSTRACT Keywords: The 2016 Fukushima earthquake and tsunami presented several new issues of tsunami generation mechanism 2016 Fukushima earthquake and tsunami and propagation, as well as of organizational responses such as evacuation procedures and dissemination of Tsunami disaster risk reduction tsunami warning. This study focuses on explanations to issues of public interest based on the experiences during Tsunami mechanism the 2016 tsunami: (1) Despite Fukushima Prefecture's proximity to the earthquake's epicenter, why was the Tsunami runup largest wave observed in the neighboring Miyagi Prefecture? (2) Why was the second wave of the tsunami larger Tsunami warning 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 Advisories at 06:02 JST. This message contained tsunami warnings for Fukushima Prefecture and Tsunami Advisories for the Pacific coast- On 22nd November 2016 at 05:59 JST (UTC+09:00), a large lines of Aomori Prefecture, Iwate Prefecture, Miyagi Prefecture, Ibaraki earthquake occurred off the east coast of Japan, near Fukushima Prefecture, and Kujukuri and Sotobo area in Chiba Prefecture. By 07:26 Prefecture. The magnitude of this normal-fault earthquake was re- JST, the Tsunami Advisories included the Uchibo Area of Chiba corded at Mj 7.4 (from the originally announced Mj 7.3) by the Japan Prefecture and Izu Islands. At 08:09 JST, Miyagi Prefecture were Meteorological Agency (JMA) at a depth of 25 km (from the originally elevated to a Tsunami Warning. At 09:46 JST, the Tsunami Warnings announced 10 km) [1]. Meanwhile, Mw 6.9 at depth 11 km was given were downgraded to Tsunami Advisories which covered Iwate by the United States Geological Survey (USGS) [2]. The shock had a Prefecture, Miyagi Prefecture, Fukushima Prefecture, and Ibaraki maximum seismic intensity of “5-” in Japanese “Shindo” scale which Prefecture. Finally, the JMA lifted all Tsunami Warnings and corresponds to VII on the Mercalli scale [1]. Advisories at 12:50 JST. As the maximum tsunami amplitude of Based on JMA data, as of 07:30 JST, further seismic activity was 1.4 m was measured at Sendai port, this was the highest tsunami recorded, which include one instance of categorized Shindo 5-, three event since 2011. instances measured at Shindo 3, seven of Shindo 2, and seven of This article provides preliminary findings of the aforementioned Shindo 1 [1]. JMA stated this seismic event was an aftershock of the issues that should be further investigated in future studies. Although 2011 Great East Japan Earthquake [1]. this earthquake and tsunami event only caused minor damages with no According to Table 1, the JMA issued its first Tsunami Warnings/ 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/). A. Suppasri et al. International Journal of Disaster Risk Reduction 21 (2017) 323–330 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. disaster risk reduction perspectives that should be pointed out and The orientation of the two nodal planes obtained from USGS (2016) correctly understood before the next tsunami event as summarized in (Fig. 2) were used for our preliminary computed initial sea surface the following section. elevation [6] based on a scaling empirical formula [7] and distribution of aftershocks [8]. Another extraordinary issue for this earthquake was 2. Emerging tsunami related issues that the fault size estimated by the mentioned scaling empirical formula is rather large with smaller slip (fault size =39×17 km2 and This section discusses five issues of public interest related to this slip =1.4 m) as shown in Fig. 2(a) but smaller fault size with larger slip tsunami event. First, while the epicenter of the earthquake was close to based on the distribution of aftershocks (fault size =20×10 km2 and Fukushima Prefecture, the highest tsunami wave was recorded in slip =4.0 m from [8] as shown in Fig. 2(b). Sendai Port, located further north in Miyagi Prefecture. Second, the second wave, rather than the first, was the highest wave. Third, the Table 2 tsunami advisory was upgraded to a tsunami warning in Miyagi Observed maximum tsunami amplitude along the east coast of Japan. Prefecture. Fourth, the local tsunami runup was observed to be higher Source [1]. than the observed tsunami amplitude at the tide gauge in Sendai Port. Finally, the tsunami propagated into rivers as undular bores. Location Amplitude (m) Time (JST) Iwate Prefecture Kuji port 0.8 07:54 2.1. The highest observed tsunami was in Sendai, Miyagi Prefecture Miyako 0.4 08:09 rather than near the earthquake's epicenter, off Fukushima Prefecture Kamaishi 0.2 08:58 Ofunato 0.4 07:56 The maximum tsunami amplitudes observed at tide gauge stations Miyagi Prefecture Ayukawa 0.8 07:39 along the east coast of Japan showed that the maximum tsunami Ishinomaki port 0.8 08:11 amplitude of 1.4 m was observed at Sendai Port in Miyagi Prefecture Sendai port 1.4 08:03 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 Fukushima Prefecture Soma 0.8 07:54 Onahama 0.9 07:06 fact that despite the epicenter being near Fukushima, its fault plane (strike angle) was perpendicular to Sendai, while parallel to other areas Ibaraki Prefecture Oarai 0.6 06:49 in Fukushima. The strike angles of two nodal planes (45–60 and 220– Kashima port 0.5 07:08 232) from all well-known sources of fault mechanism are similar [1–5]. In other words, the tsunami wave energy was spread directly towards Chiba Prefecture Okitsu 0.3 09:06 Mera 0.3 09:03 coastal areas near Sendai including wave refraction into Sendai bay. Tokyo Yaene 0.3 07:13 (Fig. 1). 324 A. Suppasri et al. International Journal of Disaster Risk Reduction 21 (2017) 323–330 Fig. 1. Location map, epicenter, location discussed in the paper. Another issue that was discovered is related to the fault size and slip should examine this kind of wave amplification. In addition, wave of this event is the earthquake magnitude. JMA finally announced Mj shoaling, refraction, and dispersive effects should also be considered 7.4 (equal to Mw 7.2 based on [9] while estimation from other inside Sendai bay. 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 2.3. Tsunami threat level was elevated from “advisory” to “warning” for M 6.9 whereas 55×21 km2 and 2.3 m for M 7.2. Such small w w in Miyagi Prefecture difference of 0.3 Mw can cause significant result of the predicted tsunami height in case of small to moderate tsunami like this event First, it is necessary to understand the current classification of the which is related to tsunami warning system. 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 2.2. The second wave was the largest 2011 Great East Japan Earthquake and Tsunami, the terminology and classification of warnings in Japan were modified [13–15]. Table 3 It is commonly understood for ordinary persons in Japan that the shows the current warning classification and description of tsunami first wave of a tsunami is the largest wave while many tsunamis showed criterion [15,16]. In order to limit complications, a wider range has the second or third wave to be the highest [10].