Can We Predict Earthquake

This is very common question and very old question also. What do you think can we? Before going to the answer we have to know the basic mechanism of an earthquake.

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Liaoning Province in northeastern Earthquake is an Example of an successful story of an Earthquake Prediction.

Liaoning Province in northeastern China began to experience swarms of small earthquakes in early 1974, but had not had a major earthquake in more than 100 years. 

They warn moderate sized earthquake within two years. 

December 22, 1974, a swarm of small earthquakes was centered around the major port city of Yingkou, so the Seismological Bureau revised their forecast to be specific, stating that the Yingkou region should expect a magnitude 6 earthquake within the next six months. 

Residents of Liaoning noticed that animals in the region began to act strangely. Pigs chewed off their tails, rats became aggressive toward humans, and snakes came out of hibernation in the depths of winter only to freeze on the surface. Water wells in the area started to bubble with gases rising from depth. 

February 4, a magnitude 4.8 earthquake shook the area

Seismological Bureau understood this to be a foreshock, and ordered 3 million people out of their homes to spend the night outside in the frigid North China winter

At 7:36 p.m. the large earthquake struck. The cities of Yingkou and neighboring Haicheng were destroyed, but instead of tens or hundreds of thousands of deaths, there were only 300 due to the successful earthquake prediction. 

BUT………

In July 1976, the city of Tang Shan, an industrial city of 1 million people located 100 miles (160 km) east of Beijing was suddenly and unexpectedly hit by a mag- nitude 7.8 earthquake at 3:43 a.m., while residents were sleeping in their beds. The city was virtually destroyed, and at least 242,000 people were killed; some estimates place the death toll much higher, closer to 800,000

Rare Big Earthquake in History

Shaanxi, China, in the year 1556. Some 830,000 people died when the earthquake hit, when their cliff-dwelling style homes that were cut into wind-blown silt (loess) collapsed. 

20 earthquakes that have caused more than 50,000 deaths and only five earthquakes have had magnitudes exceeding 9 on the Richter scale.

Likewise, in 1976 in the worst earthquake disaster of the 20th century, more than 242,000 people died in Tang Shan, China, when dual magnitude 7.8 and 7.1 earth- quakes leveled the city. In this case, the building materials were mostly unreinforced bricks, again explaining the huge loss of life. In 2004, an earthquake-induced tsunami killed an estimated 283,000 people in numerous countries around the Indian Ocean after a magnitude 9.0 earthquake off the island of Sumatra. Most loss of life in this event however resulted from the enormous tsunami that swept the Indian Ocean, not from the earthquake itself. 

Can We Predict Earthquake? NO

Lets thinks again: How to Predict Earthquake?

Recurrence intervals of past events

Earthquake forecasting based on recurrence intervals of past events is based on statistics and yields only probabilities of earthquake events happening in certain time intervals. For example, if historical records show that earthquakes of magnitude 7 occur along a segment of a fault roughly every 150 years (perhaps with a 20 year error margin, so that they really occur every 130 to 170 years), and it has been 149 years since the last magnitude 7 earthquake, does it mean that a magnitude 7 earth- quake will definitely occur along that segment of the fault in the next year? The answer is no, but that the probability of a magnitude 7 earth- quake occurring within the next 10 years is high. 

Seismic gaps

Seismic gaps are places along large fault zones that have little or no seismic activity compared to adjacent parts of the same fault. Seismic gaps are generally interpreted as places where the fault zone is stuck, and where adjacent parts of the fault are gradually slipping along, slowly releasing seismic energy and strains associated with relative creeping motion of opposing sides of the fault. Since the areas of the seismic gaps are not slipping, the energy gradually builds up in these sections, until it is released in a relatively large earthquake. If the size of the seismic gaps can be measured, and the amount of unslipped relative motion on either side of the fault measured, then the size of the impeding earth- quake in the seismic gap can be predicted. Predicting when the earth- quakes may occur in seismic gaps is another matter, and estimates must be based on recurrence intervals from past earthquakes, or predicted from estimates of when the strength of the rock in the fault zone will be exceeded and rupture (associated with the earthquake) will occur. 

Dilation 

One measurable change in rocks is called dilation, where the rock expands because of the development of numerous minor cracks or fractures in the rocks that form in response to the stresses concentrated along the fault zone. The amount of dilation may be expressed by surface bulging along the fault zone. In theory, if the strength of rocks in a fault zone is known, and if the stress across the fault zone is known, then the amount of dilation can be related to the decrease in rock strength and an estimate of when the earthquake may occur can be made. 

Other physical properties of the rocks in fault zones may also change prior to earthquakes. For instance, the velocity of seismic waves is known to change in fault zones prior to some earthquakes, and is thought to reflect changes in the number of small cracks in the rock as the strain accumulates before rupture events. 

The electrical conductivity may likewise also change, and may also be related to changes in the physical properties of the rocks. 

Foreshocks  

Sometimes large earthquakes are preceded by distinctive swarms of small earthquakes known as foreshocks. These are related to the formation of many small cracks, and may be associated with the tilting of the land surface because of the built-up strain in the rocks adjacent to the fault. With the establishment of seismic monitoring stations near active faults, these small earthquake swarms can be observed and can ultimately help warn of impending large earthquake events. 

Other possible ways to Predicts 

• Radon gas levels increase in some ground- water wells before some earthquakes. 
• Groundwater levels in wells may also drop before earthquakes, which may be related to the water filling up the many microcracks that form in the fault zone rocks before major earthquake events. 
• Perhaps most peculiar among earthquake precursors is anomalous animal behavior. Some dogs and horses have exhibited unusual and erratic behavior before some earthquakes, as have snakes, chickens, and fish that leap from the water of ponds. Why these animals behave so unusually before earthquakes is unknown, but may be related to their senses being able to identify changes in gases, light emitted from highly-strained crystals before earthquakes, or to changes in the local electromagnetic field immediately before large earthquakes. 

Learn more about EQ Prediction

https://www.usgs.gov/search?keywords=prediction+of+earthquake

Can We Predict Tsunami? 

This also can be predicted if we find the retreate scenario of the sea water from the coast to the sea then this is the sign of a big tsunami is coming.

Author:

Lecture on: Can We Predict Earthquake?

Dr. Raman Kumar Biswas, PSTU

Email: rkb07_jh@yahoo.com