Characteristics of damage to transportation facilities induced by the ground shaking and the tsunami of the 2011 East Japan mega earthquake Ö. Aydan, Tokai University, Ocean Research Institute, Shizuoka, Japan 1. Introduction The East Japan Mega Earthquake with a moment magnitude 9.0 took place at 14:46 (JST) on March 11, 2011. The earthquake was a subduction plate-boundary earthquake and the rupture area was 450 km long and 200 km wide. This earthquake caused gigantic tsunami waves, which destroyed many cities and towns along the shores of Tohoku and Kanto Regions of Japan. The casualties caused by this tsunami exceed 20,000 people. The tsunami destroyed and heavily damaged buildings of various types, transportation facilities and infrastructures. The author visited an area from Orai to Hitachi in Kanto region and Iwanuma to Rikuzentakata in Tohoku region and made observations on the damage of various structures. In this article, the author first presents the fundamental characteristics of the earthquake and induced tsunami briefly. Then the performance and damage to transportation facilities by ground shaking and tsunami are described and the findings are discussed. 2. Fundamental Characteristics of the Earthquake and Induced Tsunami The magnitude of the 2011 East Japan Mega-earthquake was estimated to be between 8.9 and 9.1, depending upon the institutions. The Japan Meteorological Agency (JMA) had difficulties to determine the magnitude of the earthquake soon after the earthquake due to several technical reasons and the magnitude was updated to 9 after several days. The earthquake occurred along the subduction zone between North American plate (NAM) and Pacific plate (PAC) and the inclination of the rupture plane was estimated to be 14-16 degrees. The faulting was due to thrust faulting with an estimated offset of 25-30 m. The seabed was uplifted by 5 m while the land sank-down by about 0.8 m with a horizontal movement of 4.6 m. The rupture initiated in the area where an earthquake with a magnitude of 7.5 was anticipated and it propagated bi-laterally. The rupture plane is about 450 km long and 200 km wide and it consisted of 4 distinct segments. There have been numerous aftershocks and some of aftershocks were greater than magnitude 7.
The aftershock activity occurred in and around the rupture area and some of shocks along the boundary between North American Plate and the Eurasian plate (EUR) took place in Shizuoka, Nagano and Akita prefectures. The rupture front stopped at the boundary between the Philippine Sea Plate (PHS) and Pacific Plate. As the stress distribution entirely changed after this earthquake, it is feared that it may initiate mega-earthquakes in Kanto, Tokai, Tonankai and Nankai subduction zones. There are several strong-motion networks in the earthquake-affected area, operated by several institutes and organizations. Following the 1995 Kobe earthquake (Hyogo-ken Nanbu earthquake), Japan established two strong motion networks, namely, KNET and KiKNET and they are operated by the NIED. The KNET network is for measuring strong ground motions at the free-field ground surface while the KiKNET network is for measuring the strong-motions at the bedrock and ground surface. The Japan Meteorological Agency also has a strong-motion network throughout Japan, which is used to estimate intensity scale and its distribution. However, the strong-motion records of this network are not always easily accessible. The Port Authority Research Institute (PARI) has a strong motion network covering the major ports in Japan and their data is accessible through the Internet. In addition, Tohoku University, Electrical Power Companies, Japan Railways, Japan Expressways (NEXCO), Building Research Institute (BRI), Tokyo University, Tokyo Metropolitan University and other institutes and organizations have their own networks. As the rupture duration of the earthquake was about 150-180 seconds, the duration of ground shaking was very long (Iwatate and Aydan, 2011). Figure 1 shows the maximum ground acceleration contours, which are obtained using the data of KNET and KiKNET. The highest ground acceleration reaching to the level of 3g was recorded at the Tsukidate strong motion station of KNET. Although the ground conditions are very good at this station, it is still difficult to understand why such a high ground motions recorded at the Tsukidate station. None of attenuation relations can estimate the attenuation of maximum of ground acceleration and velocity except the relation proposed by Aydan and Ohta [2011]. In other words, so-called NGA (Next Generation Attenuation)-like relations cannot estimate the strong motion attenuation recorded during the 2011 East Japan Mega-earthquake. In addition, one of the interesting observations regarding the strong motion records recorded by several institutes was that the records were quite dissimilar, quantitatively. The Port Authority Research Institute (PARI) operates DARTS along the shores of Japan. The DARTS are approximately 20 km away from the shore and the sea depth varies between 125 m and 204 m. The maximum tsunami height by DARTS was about
7m. There are two different definitions for characterizing the tsunami height, namely, the tsunami height at the shoreline and inundation-height or run-up height. As it was previously difficult to measure the tsunami height at shoreline, the inundation tsunami-height obtained from traces of tsunami front on the land is commonly quoted as the tsunami height in the past. This may have tremendous values depending upon how it is measured. For example, the newspapers reported a tsunami height of 38.9 m at Aneyoshi (Miyako) measured by Tokyo University of Marine Science and Technology, which probably includes the splash zone. The maximum tsunami height at shoreline in this earthquake was measured as 15.3 m at Onagawa town by the authors. Figure 2 shows the measured tsunami height together with estimations from some empirical relations. 3. Shaking-induced damage to Transportation Facilities There are several expressways and highways and Shinkansen and Local railway lines in the earthquake affected area (Figure 3). The various forms of damage to these transportation facilities are briefly described herein. 3.1 Roadways and Roadway Bridge and Viaducts There are several highways and expressways, which are affected by the long duration strong ground motions. There are major two expressways, namely, Tohoku Expressway and Jobando Expressway. While the Jobando Expressway runs close to seashore the Tohoku Expressway runs in the basins of Abukuma and Kitakami. Major parts of the expressways were built on embankments. The damage to the embankments of the expressways was caused in the form of uneven settlement and lateral deformation. The lateral deformations were generally associated with cracks running parallel to the axis of the expressways. The damage to the embankments built over soft ground was particularly severe. The major damage to the Jobando Expressway occurred near Mito (Figure 4). The embankment failed and it obstructed the traffic for about 7 days. However, the both expressways were open to traffic after several days together with restriction of speed limit and usable lanes. The causes of damage to major and secondary highways were also basically the same. The restrictions on expressways were completely lifted on March 24. The strong ground motions also caused some damage to bridges and viaducts. The basic patterns were the collision of girders with abutments, lateral offsetting girders from pedestals and settlement of the approach embankments (Figure 5). Nevertheless, the damage did not cause any major obstruction to the traffic.
There was a huge landslide on National Roadway No.4 between Shirakawa and Sukagawa, which also involved several houses next to the highway (Figure 6). There were also some rockfalls in mountainous regions. However, the scale of rockfalls was relatively small despite the mega scale of the earthquake. 3.2 Railway and Railway Bridge and Viaducts The Tohoku Shinkansen line runs almost parallel to the Tohoku Expressway. Following the 1995 Kobe earthquake, Japan Railways have been retrofitting the viaducts and bridges of Shinkansen line. However, the retrofitting of all Shinkansen lines has not been completed yet. The earthquake caused particularly in the non-retrofitted sections of viaducts near Kitakami (Figure 7). The damage to the viaducts was quite similar to those observed in the 1995 Kobe earthquake. The columns were ruptured near the top just below the platform. In addition, the reinforced concrete poles sustaining cables for the power supply trampolines of Shinkansen trains were broken. This was observed particularly in the close vicinity of Sendai City. It was also interesting to note that retrofitted columns of the viaducts were not damaged. However, it should be noted that there may be some problems to recognize the cracks which may induced by ground shaking as it is extremely difficult to see them in the retrofitted columns covered by welded and anchored steel platens. The Shinkansen line was completely operation on April 29, 2011. There was also some structural damage to Railway stations. The roof panels at Sendai station were fallen onto railways and reinforced concrete columns of buildings were fractured and spalled. In some local railway stations, the roof panels and platforms were damaged. The damage to embankments of railways passing over soft ground was observed at several localities. Furthermore, railways along some local lines were buckled due to plastic deformation of the ground and railway mounds. 3.3 Ports Some damage to ports also occurred due to ground shaking. Some of quay-walls laterally moved as a result of ground liquefaction from Kashima port in south to Kuji port in north (Figure 8). In addition, some of piers were cracked due to ground shaking and lateral movements of quays. Some cranes at several ports such as Shiogama, Kamaishi, Soma were displaced from their rails and buckling of elements did occur. However, the damage to ports by the ground shaking was light. The breakwaters and seawalls of ports from Kashima port in south to Kuji port in
north were either disappeared into sea or partially collapsed. The damage to gigantic breakwater in Ofunato and Kamaishi may have been failed due to ground shaking induced liquefaction of seabed below ruble mounds and caissons during the earthquake rather than the tsunami. There may be also additional damaging effects to breakwaters by the tsunami. The major ports affected by the earthquake and its tsunami became operation on March 24. 3.4 Airports Ground shaking did not cause any major damage to Sendai Airport. Nevertheless, a part of suspended ceilings fallen in Ibaraki Airport Terminal. This type of damage may also cause secondary disasters. 4. Tsunami-induced damage to Transportation Facilities Tsunami induced heavy damage to many transportation facilities and structures along the Pacific coast of Tohoku and Kanto regions. The damage to transportation facilities along the shorelines was particularly heavy, which are explained in this section. 4.1 Roadways and Roadway Bridge and Viaducts National roadways No.4, No.6 and No.45 running parallel to the shoreline and/or crossing rivers were damaged by the tsunami at several localities between Soma City and Yamada Town. The tsunami caused the erosion of embankments and offsetting and subsequent fall of the bridge girders (Figure 9). Most of these localities involved bridges crossing rivers. 4.2 Railway and Railway Bridge and Viaducts Joban, Sengoku, Tohoku, Onagawa, Kesennuma and Yamada Railway lines were damaged when they run parallel to shore lines and cross over rivers. The damage to railway lines occurred due to the erosion of embankments, toppling of railway piers and girder falls (Figure 10). Furthermore, the trains were carried away for a considerable distance from their original positions. 4.3 Ports Ports along the Pacific Ocean from Kashima port in south to Kuji port in north were damaged up to certain extent by the tsunami. The tsunami caused various damage to terminal buildings, quays, passenger and loading bridges, vehicles in the ports,
breakwaters, seawalls and containers (Figure 11). The inundation also caused the destruction of various equipments of the port. 4.3 Airports In the vicinity of there are two airports. One of them is Sendai airport, which is an international airport. The Sendai airport is about 1 km from the seashore and its elevation above the sea is bout 2 m. The airport and its runway was completely inundated up to 4-5.7 m. The ground level (arrival hall) was completely inundated and equipments and escalators were destructed by the tsunami (Figure 12). The arrival of the highest tsunami wave to the airport was about 55 minutes. Therefore, all airplanes could depart from the airport before the arrival tsunami. The US Army cleaned up this airport and it was partially open to the domestic air-traffic on April 13, 2011, about 1 month after the earthquake. The second airport is Matsushima military airport and it was also completely inundated by the tsunami and eighteen F-2Bs belonging to 21st Squadron, as well as other aircraft, were damaged or destroyed. 5. CONCLUSIONS The ground shaking induced by the 2011 East Japan Mega earthquake caused some damage of various extents to transportation facilities. Nevertheless, most of transportation facilities performed well during this mega earthquake except a few locations. The damage to viaducts of the Shinkansen line was particularly heavy in the Kitakami region, where retrofitting was not completed yet. This earthquake clearly demonstrated that the retrofitting the existing transportation facilities is of great importance to reduce the damaging effects of earthquakes as well as the implementation of quick recovery efforts from the earthquake disaster. The damage to the transportation facilities caused by the tsunami of the 2011 East Japan Mega earthquake was extensive despite Japan introduced many counter-measures. This partly was due to the underestimation of the magnitude of the earthquake and its potential tsunami. The damage to roadways and railways was particularly heavy inundated areas where roadways and railways cross over the rivers. The gigantic breakwater-seawalls could not perform their functions particularly due to damage caused by the ground shaking rather than the tsunami itself. The facilities at ports and airports were heavily damaged by the tsunami. However, most of the transportation facilities were operational on March 24, 2011, about two weeks after the earthquake.
REFERENCES Abe, K., Size of great earthquakes of 1837-1974 inferred from tsunami data, J. Geophys. Res. 84(B4), 1979, 1561-1568. Aydan, Ö., Ohta, Y. A new proposal for strong ground motion estimations with the consideration of characteristics of earthquake fault, Seventh National Conference on Earthquake Engineering, Istanbul, Turkey. (on CD), 2011. Aydan, Ö., Seismic and Tsunami Hazard Potentials in Indonesia with a special emphasis on Sumatra Island. Journal of The School of Marine Science and Technology, Tokai University, 2008, Vol.6, No.3, pp.19-38. Iida,K, Magnitude,energy,and generation mechanisms of tsunamis and a catalogue of earthquakes associated with tsunamis, in Proceedings, Tsunami Meetings Associated with the Tenth Pacific Science Congress, pp.7-18,int.union of Geod.and Geophys.,Paris, 1963. Japan Meteorological Agency (JMA), Tokyo, Japan Port Authority Research Institute.(PARI): Special web site for East Japan mega earthquake.http://www.pari.go.jp/info/tohoku-eq/
Figure 1: Maximum acceleration contours.
Figure 2: Comparison of observation with empirical relations for tsunami shoreline and run-up heights.
Figure 3: Major roadways and Shinkansen line in the earthquake affected area
Figure 4: Embankment failure on Jobando Expressway near Mito (from NEXCO)
Figure 5: Displaced girder north of Sendai port (from NEXCO) Figure 6: Slope failure involving National Highway R4 near Sukagawa
Figure 7: Damaged viaduct near Kitakami (picture by Prof. Takahashi, Kyoto Univ.)
Figure 8: Failed quay at Hitachi port Figure 9: Roadway bridge and its embankments damaged by the tsunami in Rikuzentakada
Figure 10: Fallen girders and toppled piers in Rikuzentakada Figure 11: Damage in Sendai port
Figure 12: Traces of damage at Sendai airport despite clean-up (April 12, 2011)