Earthquakes are one of the most common natural phenomena on our planet. It happens when there’s a sudden release of energy in the Earth’s lithosphere, creating seismic waves.
A branch of the science of seismology that is concerned with the specification of the location, time, and magnitude of future earthquakes within stated limits, specifically the determination of limitations for the succeeding strong earthquake to occur in a region, is called earthquake prediction. There are times that it is distinguished from earthquake forecasting, which is the probabilistic valuation of general earthquake hazard, together with the frequency and magnitude of damaging earthquakes in a given area over years or decades.
Earthquake prediction can be further distinguished from earthquake warning systems, which upon detection of an earthquake, give aninstantaneous warning in just seconds to nearby regions that might be also be affected. If you are looking into learning more about earthquake prediction, you’re in the right place. Today, we are giving you an introduction to the interesting science of predicting earthquakes.
Different Methods Used in Predicting Earthquakes
Earthquake prediction is considered an immature science. It means that it has not yet led to a successful prediction of an earthquake from first physical principles. Research into methods of earthquake prediction, therefore, focus on experimental analysis, with two major approaches, which are identifying distinctive precursors to earthquakes, or identifying some kind of geophysical trend or pattern in seismicity that might lead to a large earthquake.
Between the two approaches, precursors are pursued mostly because of their potential utility for short-term earthquake prediction or forecasting. Trend methods, on the other hand, are useful for forecasting, long-term prediction between 10 to 100 years’ time scale, or intermediate-term prediction between 1 to 10 years’ time scale.
An earthquake precursor is an irregular phenomenon that might give a useful warning of an approaching earthquake. Reports of these, even though commonly recognized as such only after the event, number in the thousands. In fact, some even date back to the distant past. Here are some of the precursors used in predicting earthquakes:
After an earthquake has already started, pressure waves or P-waves travel twice as fast as the more damaging shear waves or s-waves. This is not usually recognized by humans, but some animals might notice the smaller vibrations that come a few to a few dozen seconds before the main shaking. With this, animals can become alarmed or exhibit other unusual behaviors.
Based on a review of scientific studies in 2018 that covered 130 species, there’s insufficient evidence to show that animals could give warning of earthquakes hours, days, or weeks in advance. According to statistical correlations, some reported unusual behaviors of animals are due to smaller earthquakes that sometimes precede a large earthquake. If it is small enough, it might be unnoticed by humans. There were anecdotal reports of strange animal behavior before earthquakes that have been recorded for thousands of years. Some unusual animal behavior might also be mistakenly attributed to a near-future earthquake.
Most researchers studying animal prediction of earthquakes are in Japan and China. Most scientific observations, on the other hand, have come from the 1984 Otaki earthquake in Japan, the 2009 L-Aquilla earthquake in Italy, and the 2010 Canterbury earthquake in New Zealand.
The dilatancy-diffusion hypothesis was highly regarded in the 1970s as providing a physical basis for different phenomena seen as possible earthquake precursors. It was based on “solid and repeatable evidence” from laboratory experiments that highly stressed crystalline rock experienced a change in volume or dilatancy, causing changes in other characteristics, like electrical resistivity and seismic velocity. It was believed that this happened in a preparatory phase just before the earthquakeand that suitable monitoring could therefore warn of an approaching quake.
However, many studies questioned the results of this precursor, and the hypothesis eventually languished. Based on the following studies, it failed due to several reasons, which are mainlylinked with the legitimacy of the assumptions on which it was based. Aside from that, it is also biased when it comes to the selection of criteria.
Changes in Vp/Vs
Vpis the velocity of a seismic “P” (primary or pressure) wave passing through rock. Vs, on the other hand, is the velocity of the “S” (secondary or shear) wave. Based on small-scale laboratory experiments, the ratio of these velocities changes when the rock is near the point of fracturing. This was considered a likely breakthrough in the 1970swhen Russian seismologists reported observing such changes in the region of a subsequent earthquake. This effect has been attributed to dilatancy, where rock stressed to near its breaking point expands or dilates slightly.
There was a successful study of this phenomenon near Blue Mountain Lake in New York State, which led to a successful informal prediction in 1973. However, additional successes have not followed, which suggested that these predictions were justcoincidences.
Most rocks encompass small amounts of gases that can be isotopically distinguished from the normal atmospheric gases. There isinformation on spikes in the concentrations of these gases before an occurrence of a major earthquake. This has been credited to release due to pre-seismic stress or fracturing of the rock. Among these gases is radon, which is produced by radioactive decay of the trace amounts of uranium found in most rocks.
Radon is useful as a possible earthquake predictor as it is radioactive and can be easily detected. It also has a short half-life, making its levels sensitive to short-term fluctuations. In 2009, a review found 125 reports of changes in radon emissions before 86 earthquakes occurred in 1966. However, the ICEF found in its review that these earthquakes are a thousand kilometers away, months later, and at all magnitudes. With this, they have found no significant correlation.
Friedemann Freund found that water molecules rooted in rocks can separate into ions if the rock is under intense stress, based on his investigations of crystalline physics. The subsequent charge carriers can produce battery currents under certain conditions. According to Freund, these currents could be responsible for earthquake precursors, like electromagnetic radiation, earthquake lights, and the plasma’s turbulence in the ionosphere.This study is known as Freund Physics.
However, most seismologists reject this suggestion for a number of reasons. One is because stress does not accumulate rapidly before a major earthquake, and there’s no reason to expect large currents to be generated rapidly.
Rather than watching for strange phenomena that might be premonitory signs of an approaching earthquake, another method to predict earthquakes is by looking for trends or patterns that lead to it. These trends can be complex and can include many variables. That’s why advanced statistical techniques are usually needed to understand them. With this, they are also sometimes called statistical methods. Trends are also more probabilistic and have larger time periods. Here are a few examples of trends used in predicting earthquakes:
This is the estimate of the current dynamic state of a seismological system, based on natural time introduced in 2001. It is different from forecasting, which aims to guesstimate the probability of a future event. But earthquake nowcasting is also considered a potential base for forecasting. This kind of trend produces the potential earthquake score, which is an estimation of the current level of seismic progress. Some of the typical applications includegreat global earthquakes and tsunamis, aftershocks, and induced seismicity.
Based on this theory by Reid, Harry Fielding (1910), ultimately, the deformation or strain grows enough that something breaks, usually at an existing fault. An earthquake lets the rock on each side to rebound to a less deformed state. During the process, energy is released in different forms, including seismic waves. The cycle of tectonic force being gathered in elastic deformation and released in a sudden rebound is then repeated.
As the movement from a single earthquake ranges from less than a meter to about 10 meters, the demonstrated existence of large strike-slip movements of hundreds of miles shows the existence of a long-running earthquake cycle.
EMP Induced Seismicity
High energy electromagnetic pulses can induce earthquakes in 2 to 6 days after the emission by EMP generators. It also has been proposed that strong EM impacts count control seismicity because of the seismicity dynamics that follow seem to be a lot more regular than usual.
Difficulty or Impossibility of Predicting Earthquakes
Even though there has been a lot of methods used to predict earthquakes, the records have been disappointing. In the 1970s, scientists were positive that routine prediction of earthquakes would be “soon,” in about ten years, came up disappointingly short by the 1990s. Many scientists also started to wonder why. By 1997, it has been stated positively that earthquakes can not be predicted. This led to a notable debate in 1999 on whether the prediction of individual earthquakes is a real scientific goal.
Predicting earthquakes may have failed because it’s difficult, or maybe we are still beyond the current competency of science. With this, earthquake prediction may be fundamentally impossible. It also has been argued that the Earth is in a state of self-organized criticality. It means that any small earthquake has some likelihood of becoming a large earthquake. In addition, it has also been claimed on decision-theoretic grounds that predicting major earthquakes is, in any practical sense, impossible.