Racing With Seconds: Earthquake Warning Systems, Explained
By Alp Ünal AYHAN & Kaan ERTAN
It is often said it is impossible to know when an earthquake will happen. It is true to an extent, but wouldn’t it be nice to have some warning before an earthquake happens, allowing us to make life-saving decisions such as finding a place to hide and brace ourselves from the quake before a tremor hits? Earthquake warning systems do exactly this.
Earthquake early-warning systems work by detecting the non-destructive P waves that travel quickly through the earth’s crust. After detecting the wave, the system calculates the magnitude of the earthquake. If the magnitude is over the threshold, the system automatically issues a warning to all sorts of receivers such as factories, industrial facilities, subways, airports, and citizens’ cell phones. The P waves are the first messengers of an incoming earthquake. By calculating the delay between the arrival of P waves and S waves, the warning system can understand how far the epicenter of an earthquake is. After being warned of an incoming earthquake, people are in a short interval between P and S waves. This interval is the time that people can take essential precautions for the earthquake. Although this interval can be as short as 10 to 30 seconds, it is enough to help save many lives. As well as warning people and facilities of the imminent disaster, the early warning systems automatically signal factories, gas pipelines, and chemical facilities to cease their operations and secure their electricity and gas systems in order to avoid fires and explosions after the earthquake.
Earthquakes cause 4 different kinds of waves. The first one to reach the surface is the P waves (Primary waves). They are not destructive and go unnoticed by humans. After P waves, S waves (secondary waves) reach the surface, which are relatively stronger and more destructive. P and S waves are body waves that originate from the underground epicenter of an earthquake. The other 2 kinds of waves are Love and Rayleigh waves which are surface waves. As their name suggests, they travel along the surface of the Earth’s crust and despite being slower than body waves, they cause the main destruction of an earthquake. Love waves cause horizontal shearing of the ground, giving us the feeling of an earthquake. Rayleigh waves, also called as ground rolls, travel in a pattern similar to the waves of water. Rayleigh waves can be observed during an earthquake in open spaces, such as roads where the cars move up and down along with the waves.(1)(2)
The most successful and prevalent deployment of this system can be found in Japan. In Japan, this system is called Earthquake Early Warning (EEW). Japan Meteorological Agency (JMA) has 4,235 seismometers that transmit real-time earthquake information. This information is constantly analyzed by JMA and in case of an earthquake, JMA sends an alert to broadcasters, phone service providers, utility companies, and more informing them of an incoming earthquake alongside with which prefectures will be affected by the earthquake. This information is followed by the earthquake’s intensity felt by each prefecture and a tsunami alert if the data provided by the seismographs suggests a tsunami is imminent. Because the time window between the arrival of the warning and the tremor is so narrow, the alerts must be as plain and effective as possible. For this reason, EEW alerts are much simpler compared to emergency alerts from the US or Canada. Phones sound a quick siren and scream “Earthquake!” and television and radio stations play two sets of chimes followed by this voice announcement: "This is an Earthquake Early Warning. Please prepare for powerful tremors.” In case a tsunami is coming TVs are woken up from their sleep mode using signals and are automatically tuned into NHK, Japan’s public broadcaster.
Japan is not the only country to have a similar system. Taiwan also has a nationwide earthquake warning system. Mexico and Romania have employed systems that cover some regions of their land. The US and Canada are developing and testing systems that would cover their west coast.
In fact, Turkey has some sort of earthquake warning system too! Boğaziçi University has put together a network of 130 stations around İstanbul in 2001 to warn people of a possible earthquake. Despite the system being built, there are significant problems like underfunding, lack of government support, and the unwillingness of local authorities to integrate their systems to receive alerts from this system. Even though the project was started as cooperation of Boğaziçi University and the Turkish Government, the Government has repeatedly refused to fund or support the project, and not much about the system can be found online aside from a webpage of Boğaziçi University explaining it.
After a 5.8 earthquake that struck off the coast of İstanbul in September 2019, the newly elected mayor of İstanbul Ekrem İmamoğlu proposed reviving the system and letting the İstanbul Metropolitan Municipality utilize it in anticipation of a much bigger and devastating earthquake that has been expected for two decades. İmamoğlu claimed the system would give the Municipality 7-8 seconds to stop Metro trains and cut natural gas lines. It is still unclear whether his plan includes alerts to the general public through cell phone networks or broadcast stations.