Predicting Earthquakes

Predicting Earthquakes

Researchers have developed a new way to improve the prediction of earthquakes, according to a study published in the Journal of Geophysical Research: Solid Earth.

Earthquakes:

Earthquakes occur along faults (fractures between rocks which can range from a few millimeters to thousands of kilometers). Most earthquakes occur within tectonic plates, but some occur within volcanic volcanoes. There are three main types of fault: strike-slip, dip-slip, and thrust.

The difference between an ordinary quake and an earthquake is the size of the impact it has on the area surrounding the fault line.

When two blocks of earth slip past one another, seismic waves are generated in a short span of time and earthquakes occur. An ordinary quake causes no damage, whereas an earthquake can cause extensive damage to both buildings and people.

Earlier Attempts:

Many of the faults in the earth's crust slip during earthquakes because of loads acting on them, changes in stress over time, or water or other fluids under pressure.

In an attempt to understand these processes in a laboratory setting, several research groups have attempted to recreate faults and their sliding using different materials and techniques from those used in nature.

The most common technique is a shear failure of a solid rock mass due to overburden forces on a plane normal Fault.

However, the actual conditions are so complex that it is difficult to recreate them with full accuracy which makes the prediction of earthquakes difficult.

New Method:

The researchers used a statistical model to predict the frictional strength of phyllosilicates in the Earth's crust.

The researchers found that the strengthening of artificial fault zones caused by the addition of extensional forces could be diverted if they were able to control the strain distribution throughout the fault zone.

A set of equations were then formulated to predict how the frictional strength of phyllosilicate changes, along with a change in conditions such as humidity or the rate of fault movement.

This made it easier for modellers to simulate fault movement in natural conditions, including earthquakes.

The new model predicts that movement along phyllosilicate-rich fault zones becomes more difficult as it becomes faster and this has been consistent with experiments.

This behaviour of movement becoming more difficult prevents earthquakes and suggests minerals other than phyllosilicates play an important role in causing earthquakes.

However, more work and research is needed to clearly explain it and to understand the relation between the force that holds a fault together and the force needed to move the fault.

About Seismic Waves

Seismic waves are vibrations caused by earthquakes. They travel through the Earth in different ways, at different speeds, and can be detected and analyzed. The graphs below show the velocities of P-wave and S-wave propagation in different rock types.

P-waves: These are the first waves detected by seismographs (instruments used to detect and record earthquakes). These are longitudinal waves which means they vibrate along the same direction as they travel.

S-waves: These waves arrive at the detector after primary waves. These are transverse waves which means they vibrate at a right angle to the direction in which they travel.