Ten Seconds from Alarm to Quake

Twelve people dead, more than 1,000 injured, and a large number of buildings destroyed – this was the result of the earthquake that struck the East Coast of Taiwan on April 3, 2024. With a magnitude of 7.2 on the Earthquake Magnitude Scale, it was the strongest quake since the tragic Jiji earthquake in 1999 with 2,400 victims. The fact that significantly fewer people died in April is considerably due to the much improved earthquake preparation that this island nation has implemented following the catastrophe in the late 1990s: buildings are constructed in an earthquake-proof fashion; emergency responders receive better training and equipment; and regular drills prepare citizens for an emergency. In addition, this earthquake-prone island has initiated the establishment of an early warning system, similar to those that have already been in place for 20 years in California, Japan and Mexico.

Pre-empting the second wave
All of these systems are based on the different speeds at which the seismic waves spread through the Earth: primary waves move faster than the more treacherous secondary waves. As soon as seismographs installed in an earthquake zone register the first shocks, they transmit the data to a center where they are analyzed in a fully automated manner. An alarm is triggered which reaches the closest city shortly before the second, devastating, wave arrives. “The farther the epicenter is located from the respective city or region, the longer the advance notice”, explains seismologist Torsten Dahm, Head of the section Physics of Earthquakes and Volcanoes at the German Research Centre for Geosciences in Potsdam.
Unfortunately, the timing difference between the arrivals of the two types of waves is so small that early warning systems for earthquakes cannot be compared to the scale of a weather forecast. For example, Mexico City is located roughly 350 kilometers from the Pacific subduction zone where the oceanic plate of the Pacific Ocean is pushed under the continental North American plate. This scenario allows for a comparatively long advance warning time of up to more than a minute. In other regions such as Japan, only twenty seconds often remain between the warning and the quake, and in Taiwan at most ten seconds. However, these few seconds are precious, and in many situations, they can secure survival: elevators can be stopped, traffic lights can be switched to red, and critical infrastructure such as gas pipes and industrial plants can be switched off. In Japan, for example, the Shinkansen bullet trains brake automatically if a stronger earthquake is recognized along the track.

Fiber optic cables and gravitational effects
These advance warning times could be extended by a few seconds in the future; for example, by installing underwater sensors in front of coastlines – directly in those regions along subduction zones which harbor known earthquake epicenters. This would not even necessitate the use of new seismometers; in fact, according to geophysicist Dahm, the same fiber optic cables which crisscross continents and ocean floors could be used for this purpose. “This approach is still in the experimental phase, but it has shown some very promising results”, says Dahm.
He and his colleagues are also taking a closer look at what is known as gravitational effects. When large rock masses inside the Earth suddenly shift during quakes, gravity will abruptly change as a result. The signals created travel at the speed of light – much faster than the primary waves. At the moment, however, these waves can only be detected in the case of strong quakes. “Our instruments must become even more accurate to allow us to utilize these effects for the improvement of early detection systems”, explains the seismologist.

Earthquakes come without warning
This is not an earthquake forecast – these methods merely improve the reaction times to a quake that already happened. The longstanding wish for a true forecast thus remains unfulfilled. “There simply aren’t any reliable precursory phenomena, meaning, unambiguous indicators which announce strong earthquakes”, says Dahm. While certain quakes are preceded by smaller foreshocks, most are not. “This means that they are not reliable enough to allow a forecast.” When earthquakes occur, how strong they will be, and how they will travel, depends on the rock tension that builds up between the tectonic plates. “Our knowledge gap lies in the fact that we do not know the exact state of tension inside the Earth, and that we cannot measure it”, elaborates Dahm.

Tension in the Earth – measured from space
Fiber optic cables can serve yet another purpose: in cases where common seismometers only capture shocks selectively, fiber optics are capable of measuring those small deformations in the ground, which are generated by the movement of the tectonic plates, along the entire length of the cable.
The growing tension deep down becomes visible on the surface in the shape of larger and smaller distortions and faults. These changes in the terrain can be captured via radar satellites. Single measurements, however, are not sufficient to provide certainty about the state of tension inside the Earth. According to Dahm, the deformations must be measured, and analyzed, over a period of 20 to 30 years. “This is a long way that will, in the end, provide us with an important piece of the puzzle. We will be better able to estimate where strong quakes will occur.”But even if one day, earthquakes could be predicted with relative certainty, it would not be feasible from a logistical perspective to fully evacuate an entire region, or megacities like Mexico City, within hours or days, ponders Dahm. For this reason, the protection of human life in earthquake zones stands and falls with preparedness: “Earthquake-safe building remains the be-all and end-all – and certain regions leave a lot to be desired, especially when it comes to the upgrade of older buildings.”