Everyone knows about aftershocks following an earthquake, right? Residual, sometimes smaller earthquakes occur some time after an earthquake. But, did you know that a large earthquake could cause a chain reaction and cause further earthquakes in different areas?
There are two main seismic waves emitted during an earthquake: high-frequency body waves and the low-frequency surface waves. These waves both spread along the area around them but one is more damaging than the other.
The surface waves are the more destructive and are the reason that buildings fall and the ground to shake. Surface waves can travel hundreds of miles and, if they interact with other fault lines, cause extra stress to the faults and have been seen to cause brand new earthquakes. This essentially means that even if an earthquake occurs so far away that you barely feel it, within hours, or days, you could be experiencing your very own earthquake, if the original ‘quake was strong enough.
Scientific equipment measures the surface waves emitted by the quake and can predict the radius of projection they will travel, therefore indicating whether a subsidiary earthquake may occur elsewhere.
Prediction models can also be used to combat some secondary effects of an earthquake. For example: predicting a tsunami, which is caused by the shifting of tectonic plates underneath an ocean, such as the Tōhuko earthquake of 2011 (a 9.0 magnitude earthquake). A tsunami is a huge tidal wave, which continues to gather momentum until it eventually breaks. The energy and size are usually so great that this often occurs once the wave reaches land, demolishing almost everything in its path and causing countless casualties.
We know when an earthquake occurs as we can measure the seismic activity and know the time it occurred, its strength and its magnitude. With this information, and using specialized scientific equipment, we can predict if the earthquake is strong enough to cause a tsunami and, importantly, where it is likely to break and when.
Equipment and experiments into uniform accelerated motion can allow us to predict the velocity and increased acceleration of a tidal wave, giving us a prediction of how extreme the effects will be.
Ultrasonic probes, allow us to measure the frequencies of sound at great depths within the oceans. Using sound velocity equipment, we can demonstrate the Debye-Sears effect and calculate the velocity of sound through water helping us to make more accurate tsunami predictions before they occur.
Why is prediction so important?
Time. The prediction of an earthquake, as well as anticipating its effects, gives us time to prepare. Areas with a high likelihood of earthquakes have established emergency procedures for the general population. However, being able to predict secondary, interconnected earthquakes can give residents, officials and emergency services the valuable information needed to evacuate and keep out of harm's way until the danger has passed.
Breaking a Bamboo Chopstick is very similar to Earthquake Activity!
A bamboo chopstick comprises of a bunch of fibers, rather like holding a fist-full of dried spaghetti. When you break that chopstick, you’re breaking the individual fibers that snap and break at different rates, creating over 400 cracking sounds. Each fiber breaks only a little bit at a time and emits around 80 cracking sounds, with four to eight smaller cracking sounds after each of the main sounds. This is not dissimilar to an earthquake shock followed by its many smaller aftershocks. Researchers found that the bamboo chopstick doesn’t break randomly but, in fact, follows a pattern, not unlike earthquake activity, and is similar to the three main seismic power laws.
The quieter, lower energy sounds are more common than the louder, higher energy ones. The Gutenberg-Richter law explains how much more common the smaller magnitude earthquakes are than the larger magnitude ones.
The rate of bamboo aftershocks diminishes quite quickly after the main shock – again, this is very similar to Omori’s law which says that the likelihood that an aftershock will occur decreases more and more each day after the first earthquake.
As with earthquakes, Båth’s law can be used to demonstrate the ratio between the magnitude of the main shock of the first breaking fiber in the bamboo chopstick and the largest aftershock of those that follow.
These observations of acoustic emissions have been made before, in the breaking of other materials. Physics professor and co-author of the study that researched the sounds of breaking a single bamboo chopstick, Tzay-Ming Hong said, “The fact that similar research has been around and popular for a long time implies that people believe that there are profound secrets hidden behind these empirical laws and a lot can be learned by making the analogy to earthquakes.”