Practical Use of the Earthquake Early Warning (EEW) System for Shinkansen

Practical Use of the Earthquake Early Warning (EEW) System for Shinkansen Shinji Sato, Kimitoshi Ashiya, Shunroku Yamamoto, Naoyasu Iwata, Masahiro Korenaga, and Shunta Noda Railway Technical Research Institute, Hikari-cho, Kokubunji, Tokyo Japan 1. Introduction Japan is a distinguished country of earthquake occurrence in the world. 100,000 earthquakes or more are recorded every year according to the published data of the Japan Meteorological Agency (JMA). This means that about 300 or more earthquakes occur per a day on the average somewhere in Japan. According to the Cabinet Office, the Government of Japan, Japan accounts for about 20% of all the M6 or more earthquakes occurring in the world. In view of this situation, Japan National Railway (JNR) had established a lot of counter measures for a long time. In order to decrease the earthquake damage of the railway soft measures such as stopping the train immediately after the earthquake occurrence before a big shake reaches to the train are important in addition to hard measures such as earthquake resistance improvement of the structure and installment of the derailment measures etc. We have promoted development of the Earthquake Early Warning (EEW) system which surely catches the P-wave, judges the range of the earthquake damage generation from this information instantaneously, and stops the train operation. Here, the research and development of the practical use of the EEW system for Shinkansen, details of the system and the study to be continued for the future will be described. 1960 1980 2000 2009 Niigata Pref. (1964) M7.5 Ooi river (1965) M6.1 Tokachi Off (1968) M7.9 Southwest Off Hokkaido (1993) M7.8 South Hyogo Pref. (1995) M7.3 Miyagi Off (1978) M7.4 Middle Japan Sea (1983) M7.7 Kushiro Off (1993) M7.5 Mid Niigata Pref. (2004) M6.8 Niigata Pref. Chuetsu Off (2007) M6.8 The 1st generation The 2nd generation UrEDAS (1992 2004) Compact UrEDAS (1996 2004) The 3rd generation EEW seismograph (2004 ) Fig.1 Development of EEW system for Shinkansen

2. Development of EEW system for Shinkansen Fig.1 shows the development of the practical use of the EEW system for Shinkansen. The first generation of development is installment of a seismograph that outputs warning when the shake more than the criterion is detected. In the second generation of development, the EEW system estimate the amplitude of the shake of S-wave by detecting P-wave was put to practical use. When the Seikan undersea railway tunnel was opened to the commercial use, UrEDAS (Urgent Earthquake Detection and Alarm System) that was the EEW system for railway was put to practical use for the first time in 1987. At that time UrEDAS didn t stop the train directly and only had the function to display the information where the earthquake had occurred on the train control panel. UrEDAS had been improved since then, and its practical operation was started for the first time in the world as a system that had the warning judgment and train control function along with introduction of Tokaido Shinkansen "Nozomi (300 series)" in 1992. In addition, when Hokuriku Shinkansen (between Tokyo to Nagano) started a business in 1998, Compact UrEDAS of which P-wave detection technique improved, was introduced. In the third generation development, a new seismograph was developed that was equipped with P-wave detection algorithm was put into practical use (4). The reason why this system could be easily installed into Shinkansen system was become Shinkansen system is such that it can be easily integrated with this system. The railway is a system in which the ground equipments, the vehicles, the signals, communication systems, operation, and management etc. are highly integrated. The Shinkansen vehicle has the function that an emergency brake operates automatically when power supply is stopped. Integrating such Shinkansen vehicle s function with the Shinkansen substation function to stop power supply automatically linked with the operation of the seismograph, the EEW system has been developed to be used as a software countermeasure against the earthquake damage for Shinkansen. There is no precedent for introduction of similar systems in the transportation fields such as the road and air transport in Japan. 3. Feature of EEW system for Shinkansen 3.1. System Structure In this system, it is a prerequisite that, in order to secure the maximum reliability as an earthquake disaster prevention system used in the railway, the system should operate if only one seismograph is functioning. This system is composed of two kinds of seismographs namely the seismographs installed along the railway-tracks to detect an earthquake occurring along the railway-tracks or large scale earthquakes and the Coast line seismograph installed in the places other than the area along railway-tracks, a relay server and a supervisory terminal which consolidates received from the seismographs and monitor system. There is EEW system of the JMA with a similar function. The difference between our system and JMA exists in the warning judgment part. To cope with occurrence of the troubles of the power supply and the communication, our system does the warning judgment and the trains stop judgment with only one seismograph, while in the JMA system, the

warning judgement is done at the control server Fig.2 shows the comparison of the respective system configurations. The function of each seismograph is now explained as follows. Fig.2 Difference between EEW system for Shinkansen and the one for JMA 3.1.1 Railway-tracks seismograph This is a seismograph set up in the substation to cope with the earthquake that occurs in the places along the railway-tracks. Moreover, this seismograph cuts off a power supply to stop Shinkansen trains by outputting 24V contact signal when the earthquake occurs. The purpose of setting up the seismograph in the substation is to surely transmit 24V contact signal to the substation. On the other hand, although it is advantageous to set up the seismograph in the substation from the view point of transmission of information, the protection equipment and the seismograph must be so prepared as to cope with the electromagnetic influence of the adjoining transformation installation that deals with AC2,500V. 3.1.2 Coastline seismograph The coastline seismograph is a seismograph set up along the coastlines to detect promptly the large-scale earthquake that occurs in the vicinity of an ocean deep. It is sometimes set up outside the right of way. In that case, there is no big difference between coastline seismograph and that of JMA with respect to the installation environment.

Both the seismograph along the railway-tracks and the coastline seismograph have the detection function of the P-wave and S-wave. Moreover, a mechanical seismograph that keeps operating for a long time even if the power supply is cut off is juxtaposed to cope with breakdown of the seismograph for EEW. Fig.3 shows each seismograph. Fig.3 Seismograph system (Left EEW seismograph Right mechanical seismograph) 3.2. Earthquake detection and train stop judgment technique Generally, P-wave reaches the railway track concerned earlier then S-wave. If the scale of earthquake (magnitude) and the epicenter can be known before S-wave of the large amplitude reaches the railway tracks, the braking instruction can be given to the train ahead of time, and consequently the safety of the train operation during earthquake occurrence can be improved. Here, the detection method of the P-wave and S-wave, and how to judge the train stop will be described. 3.2.1. P-wave detection and train stop judgment technique Within 1 to 2 seconds after detecting P-wave, the EEW seismograph estimates the earthquake parameters namely epicentral distance, epicentral azimuth, and magnitude as shown in Fig.4. We call this estimation process B - Δ method. In addition, the range of damage area is estimated from the estimated epicentral distance and magnitude using the empirical equation. We call this estimation process M - Δ method. Using these two methods, EEW seismograph judges train stop (power supply cut off), only in the case EEW seismograph (observation site of Fig.4) is located within the estimate damage area. Earthquake parameter estimation (B - Δ method) and M - Δ method will be explained in the following.

Epicenter Estimated Damage Area Depends on Magnitude North Estimate Epicenter Estimated Azimuth Observation Site Fig.4 P-wave detection and warning judgment method (a) B Δ method Generally, the P-wave propagates the site concerned the earliest among the seismic ground motion elements, and wave velocity is 5 to 7 km/second in the bedrock. We will briefly explain here the outline of the method of estimating earthquake parameters based on the P-wave (Refer to Odaka (2) for details). The EEW seismograph for the Shinkansen system always measures the acceleration data in the three components (NS,EW,UD) with 100Hz sampling. The IIR filter processing for P-wave detection is applied to the obtained acceleration data as shown in Fig.5. Next, the fitting processing by the eq.(1) is applied to the envelope curve of the absolute value of amplitude of UD component of the data obtained within 1 to 2 seconds after earthquake is detected. Frequency(Hz) Fig. 5 IIR-Filter design for P-wave detection.

y(t) = Bt exp(-at) (1) Coefficient B included in the above eq.(1) indicates the tendency of the amplitude increment of the first movement part of P-wave, and it is confirmed that it has a good correlation with the epicentral distance as shown in Fig.6. The epicentral distance is obtained from the tendency of the amplitude increment of the first movement part of P-wave (Coefficient B) by using this relationship. Fig. 6 Relationship between the coefficient B and the epicentral distance Δ If the epicentral distance is estimated, the magnitude is calculated by the empirical equation prepared beforehand that shows the relation between the peak magnitude and the epicentral distance. When a large earthquake occurs, the magnitude that increases gradually is calculated accurately by keeping analyzing the maximum amplitudes every sampling. Fig.7 shows the estimation process of these earthquake parameters. Amplitude Earthquake Detection Data Length (1-2 second) P-wave S-wave Amplitude Increase Ratio Epicentral Distance Maximum Amplitude Time Epicentral Distance Magnitude Fig. 7 Estimation process of earthquake parameters by a new seismograph

(b) M - Δ method Next, we will explain the processing how to control the train operation based on the estimated epicenter distance and magnitude. The train stopping is decided in case the extent of the shake of structure reaches the level at which the structure will be damaged. For this decision, it is necessary to accumulate the various records of the past earthquake damages. M Δ diagram is prepared based on these records of the past earthquake damages (Refer to Fig.8). In Fig.8, the past damage records are plotted, and the area where the plotted data are enveloped should be the train control area (Fig.8 shaded part). For instance, the decision to stop Shinkansen train is executed at once, in case an earthquake occurs and its estimated magnitude is 7 and its estimated epicenter distance is 20km, because the data consisting of M and Δ is contained within this area. This technique was adapted along with the practical use of UrEDAS in 1992, and has been reviewed every time a damaging earthquake occurs. It can be said that this M Δ figure offers a simple and reliable train stop decision technique because decision is executed based on two parameters of the estimated epicenter distance and the estimated magnitude. Fig.8 Relationship between Magnitude and Epicenter( Δ ) 3.2.2. S-wave index The vector amplitude of horizontal 2 components acceleration that passed the JR warning filter (JR filter) is used as an index to controls train driving for both Shinkansen and domestic railways. The JR filter is based on the design standard of the filter established on as JNR standard in 1984. Fig.9 shows frequency characteristic of the JR filter. It is understood that pass-band of this filter is corresponding to predominant frequency of P-wave and S-wave. When the horizontal, vector amplitude exceeds 40gal S-wave is issued.

Fig.9 IIR-Filter Design for S-wave alarm 3.3. Communication between seismographs After Shinkansen derailment by the Mid Niigata Prefecture Earthquake (2004), the earlier alarm output has been demanded by JR companies. The function of information exchange on P-wave warning among the seismographs along the railway-tracks has been newly added to the system of the third generation. This function is called a seismograph two-way communication function, and is shown in Fig.10. Thanks to this function, a prompter warning judgment has become possible because the warning judgment can be made even in the region where neither P-wave nor S-wave has arrived. Fig.10 Seismograph two-way communication 4. Simulation for the Mid Niigata Prefecture Earthquake in 2004 The operation simulation of the seismograph in the Mid Niigata Prefecture Earthquake (2004) has been executed based on the judgment technique of warning of the P-wave and S-wave that has been shown up to now, and lead-time after giving warning has been examined. The earthquake data used

is those of K-NET of National Research Institute for Earth Science and Disaster Prevention (NIED) recorded within 20km from the epicenter. It is thought that the operation of the actual JR seismographs have recorded also almost the same data. The arrangement of the seismographs is shown in Fig.11 and the simulation results are shown in Table 1. Shin-Etsu line Nagaoka Ojiya Jyo-Etsu Shinkansen Nagaoka-Shisho Epicenter Tadami line Koide Tookamachi Iiyama line Jyo-Etsu line Fig.11 Arrangement of the seismographs ( site of seismograph of NIED) Table 1 The simulation results Site Name Epicentral Distance Manual Detection time Simulation result Lead-time (sec) P-wave arrival time S-wave arrival time P-wave warning time S-wave warning time Ojiya 7.05 17:56:02.93 17:56:03.50-17:56:03.74 - Koide 10.60 17:56:03.42 17:56:04.27 17:56:04.35 17:56:06.92 2.57 Nagaoka-shisho 15.11 17:56:03.90 17:56:06.30 17:56:04.15 17:56:08.02 3.67 Nagaoka 16.87 17:56:04.07 17:56:06.65 17:56:04.84 17:56:07.29 2.94 Tookamachi 21.02 17:56:05.40 17:56:11.90 17:56:10.33 17:56:12.88 8.53 According to JMA the earthquake occurred at 17:56. P-wave warnings were issued from all station except Ojiya. In Ojiya P-wave warning was not issued, because vertical motion was extremely larger than criteria, S-wave warning was issued immediately after P-wave arrival. From the result shown in Table 1, Lead-time is estimated to be almost 3 seconds in the neighborhood of the epicenter. It is thought that the benefit of the lead-time is limited for the trains running in the vicinity of the epicenter because Shinkansen trains need a few minutes to be stopped. However, it is considered that the benefit of the lead-time is high for the trains that run in the area from the epicenter.

5. Improvement of seismograph To stop Shinkansen as fast as possible after the earthquake is detected, the seismograph is basically arranged in the substation placed along railway-tracks. However, it is necessary to consider the occurrence of the malfunction by the electromagnetic radiation which is usually strong in the substation. Therefore, reliability improvement of the hardware of the seismograph for the electromagnetic radiation is expected. In order to apply the EMC standard to the seismograph quantitative evaluation the tolerance to the electromagnetic radiation carried out now. EMC standard is a standard by which it is proven to make the influence given to no disorder of operation even if the electromagnetic radiation influences an electronic equipment such as seismographs or nor other electronic equipment a minimum. First of all, the electromagnetic radiation of strength of the electromagnetic radiation around the seismograph was measured in the substation where the seismograph was set up. Seismograph EMC examination based on IEC61000 was executed in special equipment based on this test result as shown in Fig.12. We considered the test result, and a new seismograph is being produced now. We will want to judge right or wrong of the adoption as seismograph EMC specification while seeing the effect of a new seismograph. Fig.12 The EMC test for Seismograph 6. Summary Here, we presented the details of the EEW system in Japan and a concrete content of the EEW system now in use. The seismograph used in the Shinkansen system has the P-wave and S-wave warning function. Moreover, power supply can be stopped when judged as dangerous by each seismograph. In addition, earthquake information can be exchanged among the seismographs, and even the seismograph to which P-wave has not reached yet has the function to do the warning judgment. This system is actually operated for Shinkansen now. We think that based on the

experiences up to now, it is necessary to continue the research and development of the algorithm concerning a prompter warning judgment (software) and the composition equipment (hardware) that does the steadier operation. Further, in view of the coming Shinkansen speed up to more than 300km/h, various approaches should be examined in future, aiming at achieving more reliable EEW system, while corresponding flexibly to the change of the railway system. Reference (1) Cabinet Office, Government of Japan, Outline of earthquake measures of our country, http://www.bousai.go.jp/jishin/chubou/taisaku_gaiyou/pdf/hassei-jishin.pdf (in Japanese) (2) Odaka T., Ashiya K., Tsukada S., Sato S., Ohtake K. and Nozaka D.: A new method of quickly estimating epicentral distance and magnitude from a single seismic record, Bull. Seism. Soc. Am., Vol.93, No.1, pp.526-532 (2003) (3) Tsukada S., Odaka T., Ashiya K., Ohtake K., Nozaka D.: A new algorithm for EEW system using P-wave envelop, Zishin2, Vol.56, No.4, pp.351-361 (2004) (in Japanese) (4) Sato S., Taya S., Ashiya K.: Development of seismograph for warning that uses new earthquake parameter presumption algorithm, RTRI Report, Vol.16 No.8, (in Japanese) (5) Iwahashi H., Iwata N., Sato S., Ashiya K., Practical use of earthquake early warning system, RTRI Report, Vol.18 No.9, (in Japanese)