Early Earthquake Warning Systems

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1 Early Earthquake Warning Systems Faisal Masood 1 1 National University of Computer and Emerging Sciences, Lahore; l165172@lhr.nu.edu.pk Abstract Seismic activity poses a great risk to densely populated modern urban centers. Technical advancements in seismic sensors, telecommunication equipment and personal connectivity provide fundamental components for an earthquake early warning system. Life threating effects of a high magnitude earthquake can be largely reduced by providing an early warning of few seconds to few minutes before arrival of devastating seismic waves. This paper reviews some of the recently deployed earthquake early warning systems. In particular, currently deployed systems and their effectiveness are identified. Keywords earthquake; early warning; P- Wave; S-Wave; seismec hazard. I. INTRODUCTION All of the recent earthquake early warning systems (EEWS) are based on the fact that warning message can be transmitted at a much higher speed as compared to the seismic waves from the earthquake which travels through the Earth s interior at a speed of a few kilometers per second. When an earthquake begins, seismic waves of two distinct types radiate outward from the origin of earthquake, also known as the epicenter. First type is P waves which are compressional in nature while others are S waves which are transverse in nature. The most pronounced effect of faster yet weaker P wave is detected by nearby sensors. As a result, an alert signal is sent out using high speed communication links to provide ample time (few seconds to minutes) for people, trains, nuclear power plants and other automated industrial systems to take immediate protective action before the arrival of the slower, stronger and potentially destructive S waves. Custom made radio units, computers, mobile phones and other alert publishing devices receiving the alert messages can calculate the expected arrival time and estimate the intensity of shaking at a desired location. Earthquake is a condition of earth in which kinetic energy is suddenly released at a fault in the Earth s crust. In some cases, a rupture is created which begins to move and extend along the fault like a crack in a glass. The sudden release of kinetic energy from the fault area begins to radiate outwards in all direction especially on both sides of the fault. This energy is radiated in the form of seismic waves and it travels through the earth s crust. After travelling at varying speeds depending on the rock formations inside earth s crust, these waves reach the earth surface and cause the ground shaking and jolting which in turn wreak havoc on the man mad structures. The science of predicting an earthquake is in its infancy; however, the technology for detecting an earthquake closer to its epicenter and dispatching a warning message for surrounding communities exists. Earthquake early warning systems implement the above mentioned functionality by detecting seismic waves in the early phases of an earthquake. After calculating the expected magnitude of shaking, EEWS sends alerts to the people and electronic devices before the arrival of damage causing waves. The concept of early warning is solely dependent on the difference between the speed of information travel and speed of seismic waves traveling through the dense interior of earth. The traveling speed of seismic waves is measured to range from 1 to 6 kilometers per second. At this speed the devastating S-Waves will take anywhere from few seconds to few minutes from epicenter to an area of interest. There are three essential components of an earthquake early warning system; the sensors, the processing algorithms and the communication infrastructure. The EEWS need to be very quick in detecting an earthquake, processing its feature like magnitude, epicenter location and propagation speed, and relaying this information through a high speed communication link to outpace the destructive waves of oncoming earthquake. A mass notification dispatch system is also necessary to timely warn large masses of an eminent shaking. Typical EEWS provides a reaction time of few seconds to few minutes before strong tremors 73

2 arrive. Another parameter which determines the amount of warning time is the distance of an end user from the epicenter. Areas very close to an epicenter usually don t get enough reaction time before the arrival of strong tremors. Contrary to that, areas at a greater distance from epicenter get a relatively higher reaction time. The network of seismic sensors needs to be densely populated to cover all possible sources of an earthquake. A densely deployed network provides another advantage by reducing the dead zone near epicenter and hence protecting more people. The remaining of this paper is organized as follows; section II presents four of the recently deployed earthquake early warning systems while section III provides a critical analysis of existing techniques in earthquake early warning systems. Section IV summarized the challenges in this filed and section V comments on conclusions. II. DEPLOYED SYSTEMS Japan was among the first few countries where an earthquake early warning system was deployed. The second noticeable system is developed by United States Geological Survey which deployed an EEWS in California. Taiwan has an experimental system for earthquake warning and Italy is working on a similar system in southern areas. A. EEWS in Japan Japan has a fully deployed and most advanced earthquake early warning system in the world. The Japanese EEWS system was launched in 2007 along with an online alert system for wide spread publishing warning messages. This system uses more than one thousand (1000) seismographs to detect tremors, both small and large. It estimates the epicenter of an earthquake and sends out elaborate warning messages on multiple channels. Due to the geographic orientation of Japan, the aforementioned seismographs have to be scattered throughout the country and along the lengthy sea shores of the Japan. The Japan Meteorological Agency collaborates with the National Research Institute for Earth Science and Disaster Prevention to broadcast the earthquake warnings. It is worth noting that Japanese Railways has its own largescale earthquake early warning system which was launched about 20 years ago to assure the safe operation of Japan s superfast bullet train. Warnings from this system are used to immediately stop the bullet trains in case of an earthquake. B. Shake Alert USA Shake Alert is an experimental project under development by USGS since First alerts were dispatched to a selected group of test users in early The detection nodes used for Shake Alert system were already deployed for seismic activity monitoring. One of these networks is the 400 node California Integrated Seismic Network(CISN) operated by USGS for ground motion detection. The University of California, Berkeley, California Institute of Technology and the State of California are the key partners with USGS to look after the CSIN. The second network is Pacific Northwest Seismic Network (PNSN) made possible by collaboration between University of Washington USGS, and University of Oregon. Both of these networks form the Advanced National Seismic System (ANSS). Shake Alert leveraged both of these regional networks and extended their research activities. An elaborated postearthquake warning system was built and tested. After the experimental stage, a fully deployed Shake Alert system will dispatch earthquake warnings using all available communication links, including but not limited to Wireless Emergency Alerts by FEMA and Integrated Public Alert and Warning System, social media networks, cellphone apps, and other electronic warning technologies of the future. Currently selected test users of experimental Shake Alert system use a computer application to get the early warning messages in the form of both visual and audible alerts. When an earthquake is detected by the Shake Alert, a warning message is transmitted to the test users in the form of a location map for the earthquake epicenter. The computer application also depicts the waves emitted from the epicenter and moving toward the test user location. An estimated magnitude of tremors is also shown along with the arrival time of the strong earthquake waves for the user s location. An audible alert sound is generated along with a voice message counting down for the arrival time of strong shacking and spelling out expected magnitude [4]. 74

3 C. EEWS in Taiwan Central Weather Bureau of Taiwan joined hands with the National Center for Research on Earthquake Engineering in 2009 to implement the country s first version of earthquake early warning system. Two other national institutions that played a vital role in this critical development were National Science and Technology Center for Disaster Reduction and National Center for High-performance Computing. Situated near Manila and Ryukyu trenches, Taiwan is one of those countries which are most vulnerable to the seismic activity. This active seismic belt on the west side the Philippine Sea, urged authorities to implement an early warning system to reduce the risk and loss associated with large earthquakes. Like other systems of similar nature, the EEWS of Taiwan was designed on the principle of speed difference between earthquake waves and RF waves. As soon as the occurrence of an earthquake is detected, the EEWS publishes a warning on multiple channels in a hope to enable people for necessary precautions. In 1992, a second phase of EEWS was launched by the Central Weather Bureau. This phase was named the Taiwan Strong Motion Instrumentation Program and its main aim was to gather detailed knowledge about seismic activities in the region. Another salient feature of all these EEWS related efforts was spreading of awareness among local residents regarding newly installed warnings. These training exercises provide the necessary training for quick decision making in case a strong earthquake hit the area. People on the first and ground floors were advised to flee the building and reach open areas, while those living on higher floors are advised to crouch under the tables or other strong structures. These social aspects of EEWS are especially helpful in saving lives of larger gatherings like schools and factories. D. EEWS in Italy An earthquake monitoring system has been recently deployed in southern parts of Italy along the Apenninic belt. This deployment was done to test the feasibility of a large scale earthquake warning system in the seismically active areas of the Italy. The final system will issue a warning message in near real time using a location map of epicenter and estimated magnitude of the upcoming earthquake. The first part of this monitoring system is deployed in the Campania-Lucania area which is very close to an active normal fault. A dense network of seismic detectors is commissioned in an area where several high magnitude earthquakes have occurred during last few centuries. Recent geological studies in this part of Italy suggest that there is a high probability of a large earthquake with a magnitude of 5.5 or higher in near future. The detector part of this EEWS comprises of 30 seismic sensor stations and 5 data processing centers called local control centers. All detector stations are equipped strong-motion accelerometer and velocity meter having 1-sec natural period. This choice of sensors and deployment scheme guarantees a relatively wide dynamic recording range. To further optimize the recording of regional seismic events, five sites are fitted with broad spectrum velocity sensors. The seismic data is transmitted to local control centers from all of the 30 seismic detector stations using a point to point Wi-Fi link. A quick preprocessing of data is done at local control centers for generating automatic reports of detected events and for generating a detailed archive. The main Network Control Center is located in Naples at a distance of 100 Km from the seismically active area and is connected to the local control centers over a high speed radio link. The detailed analysis of data is performed at the network control center using multiple algorithms on server grade computers to estimate the magnitude, epicenter location, and maximum ground motion at different distance from epicenter. Final warning for the end users is also generated from the network control center. III. CRITICAL ANALYSIS Earthquake early warning systems are considered to be the most efficient and powerful tool to mitigate earthquake disasters. The system has several technical limitations, EEWs are responding too slowly for places which are near the epicenter. For an earthquake of more than 7 magnitudes, rupture usually continues for more than 10 seconds, in such cases the first warning is disseminated in the middle of the rupture. Because of such technical limitations it is difficult to estimate the intensity and accurate magnitude of the earthquake. Moreover, it is difficult to separate the two earthquakes when 75

4 two or more than two earthquakes occurs in succession. Estimation of magnitude and hypocenter is not processed accurately; therefore, the error in the anticipation of seismic intensity becomes large. Currently, Earthquake warning system around the world face three major difficulties, which include; (i) Limitation of hardware, (ii) Technical difficulties; after the occurrence of earthquake, it is difficult to determine the basic parameters of earthquake i.e., magnitude and intensity of earthquake, if number of stations are limited (iii) Early Warning; getting early information about an earthquake is not a solution, to spread the information it is important to develop awareness among the users [7]. There are certain limitations associated with USA EEWS. As an example, no warning will is possible in a warning zone. Currently the system deployed in most of the countries takes minimum ten seconds to send a notification after detecting an earthquake. This means that people residing closer to the epicenter may not get a sufficient time to take protective measures. Only those residing outside 20 miles radius from epicenter may receive a warning providing them a few seconds for getting to a safe place. Those who get the warning may not experience any shake by the time earthquake reaches them. Within the San Francisco area, sensors are placed at 10 to 20 kilometers apart. More than 560 sensors are placed in different areas of California to measure and detect the intensity of earthquake [6]. USA shake alert will cost $16.1 million per year; this system cost includes a one-time investment as well as expenses for ongoing improvements to upgrade the instrumentation, research and development and state of the art methods. The system also requires an annual operational and maintenance cost of $4.7 million. In order to fully implement the system three steps need to be taken; (i) development of technology to provide accurate information to the general public, (ii) awareness and (iii) educating the masses about the meaning of warnings and investment in the seismic infrastructure to improve the efficiency of detection of earthquakes. Currently the mass messaging technologies are too slow for earthquake early warning systems. However, most likely the technologies used to spread the warning includes; text messaging, national integrated public alert and smartphone apps [6]. In United States, a prototype design was developed to mitigate the consequences of aftershocks. The system was primarily composed of four components; motion sensors, central server, radio receivers and repeaters. The prototype system detected 18 events out of which 12 alerts were recognized with only one false alarm and 2 miss trigged [1]. According to Japan meteorology agency there are three major limitations within the EEWS. The first and foremost is that the time window for the announcement of an earthquake is very short: of the order of a few seconds or a few minutes. The warning may not be sent to the areas that are close to the origin of the earthquake. Second limitation is false early earthquake warnings may occur due to device failure, noise or lightening. The third limitation is related to magnitude estimation: For large earthquakes, there are certain limiting factors to the accuracy of magnitude estimation of an earthquake. Since its inception in Japan in 2007, the main issue with the modern EEW system is the false alarm and flawed reading, which was produced because of electrical noise. Interruption of electrical current disturbing the cables and sensors is a common cause of false alarms in these systems [9]. To further elaborate the issue of false alarms, the Japanese agency of metrology has experimented and developed a mixed single station in the last decade with a network based early warning system, to intimate the general public about a disaster. During the period of , the Japanese metrological agency sent 588 earthquake early warnings out of which 27 were recognized as false alarms [2]. Major cities of Taiwan are located too close, i.e., less than 100 km, to an active seismic zone. This proximity defies the basic premise of the early warning system for the public. The current earthquake warning system of Taiwan consist of 108 seismic stations, but the time duration of giving out an alert is far more than the systems used in USA and Japan. Taiwan EEW provides alerts within the 20 seconds of an earthquake which is at least twice as large as Japanese EEWS. The system has other limitations in the 76

5 form of missed alerts and false alarms [10]. Time duration of 20 second is considered very long for an EEWS, which can be improved if the density of seismic stations is increased; however, a very high cost is incurred to build a high density seismic network [3]. The earthquake warnings are displayed on LED signs in Taiwan. The system gives a warning 10 seconds before the earthquake strikes, while the earthquake warnings are sent through cellular network using text messages. LED signs are considered faster than televisions. Television needs to remain on to capture a warning at appropriate time and requires three to five seconds to be turned on [5]. The EEWS of Taiwan performed fairly well on detecting earthquake event. The Taiwan Central Weather Bureau implemented a virtual sub network. From December 2000 to December 2001 the system successfully recognized all of the 56 events occurred during that year [8]. IV. CHALLENGES Development and implementation of EEWS has been rapid in the past few years to overcome the hazardous damages of earthquakes. But there are many challenges to overcome for the successful implementation of these systems around the globe. The first and the most important challenge is that the present EEWS can t identify source finiteness. The real time mapping and recognition of the finite fault sources can enhance the performance of EEW system in terms of accuracy and warning times. Another big challenge is to implement the EEWS in the earthquake-prone regions before a large earthquake. This task requires huge funding and widespread collaboration between multiple nations. Public education is another challenge for the effective use of the EEWS. The methodologies and experiences related to the implementation of the EEWS and dissemination of warnings must be efficiently communicated among the experts and the general public. Activation of the EEWS for smaller and more frequent earthquakes is another big hurdle in this field. These smaller jolts vanish quickly and people are annoyed due to the alarms with no apparent shaking. Present EEWS are activated and became functional after many years of development, installation and testing [2]. V. CONCLUSIONS Natural disasters are not just limited to any specific region or type but around the globe the most disastrous calamity is the earthquake. During an earthquake shaking waves travel at a speed of 2 miles per second. By detecting these waves through a sophisticated network of seismometers, accelerometers and alarms we can lessen the threats posed by the approaching earthquake. Warning of the earthquake within seconds to tens of seconds of a seismic activity through the EEWS can help implement the earthquake preventive measures. Warning time of EEWS is directly dependent on the distance between the user and the earthquake epicenter and may range from few seconds to a few minutes. Implementation of earthquake early warning is increasing around the world due to an increased awareness about the threats posed by earthquakes, methodological development and seismic network expansion. Most developed countries of the world like Japan, Mexico, China and the United States have installed these systems so that a pro-active approach would be opted to deal with disasters. Until now only Japan has the nationwide network of earthquake early warning system while rests of the countries have a wide network of these systems protecting their important places. With the rapid development in methodology, more sophisticated and real time EEWS are being experimented in many countries of the world. REFERENCES [1] R. Allen, "Earthquake detection systems can sound the alarm in the moments before a big tremor strikes time enough to save lives", Scientific American, Berkeley, CA, USA, [2] R. Allen, J. Mori, M. Yamada and H. Kanamori, "Earthquake warnings in Japan Building the system, and warnings for the2011 Tohoku-oki earthquake", Earthquake early warning summit, Berkeley, CA, USA, [3] N. Hsiao, Y. Wu, T. Shin, L. Zhao and T. Teng, "Development of earthquake early warning system in Taiwan", Geophysical Research Letters, vol. 36, no. 2, pp. 1-5, [4] D. Given, E. Cochran, T. Heaton, E. Hauksson, R. Allen, P. Hellweg, J. Vidale and P. Bodin, "Technical implementation plan for the ShakeAlert production system: an Earthquake Early Warning system for the West Coast of the 77

6 United States", Open-File Report, pp. 1-25, [5] G. Kuo, "Taiwan earthquake alert system saves lives", TAWIAN TODAY, [6] M. Olivieri, R. Allen and G. Wurman, "The Potential for Earthquake Early Warning in Italy Using ElarmS", Bulletin of the Seismological Society of America, vol. 98, no. 1, pp , [7] J. Moßgraber, F. Chaves, S. Middleton, Z. Zlatev and R. Tao, "The Seven Main Challenges of an Early Warning System Architecture", in Proceedings of the 10th International ISCRAM Conference, Baden-Baden, Germany, 2013, pp [8] Y. Xu, J. Wang, Y. Wu and H. Kuo-Chen, "Reliability assessment on earthquake early warning: A case study from Taiwan", [Online]. Available: [Accessed: 16- Nov- 2017]. [9] E. Yamasaki, "What We Can Learn From Japan's Early Earthquake Warning System", Repository.upenn.edu, [Online]. Available: /2. [Accessed: 16- Nov- 2017]. [10] N. Hsiao, Y. Wu, L. Zhao, D. Chen, W. Huang, K. Kuo, T. Shin and P. Leu, "A new prototype system for earthquake early warning in Taiwan", Soil Dynamics and Earthquake Engineering, vol. 31, no. 2, pp , ABOUT THE AUTHORS Faisal Masood is currently doing his M.S. in electrical engineering from National University of Computer and Emerging Sciences, Lahore, Pakistan. 78