Paleoseismology (Studying old earthquakes) shows that most of the earthquakes occur along active faults. Surveying these faults delineates “seismic region” or location of probable earthquakes. Integrating data about past earthquakes and projecting them on a map will show risky areas better.

Statistical survey of major earthquakes in an area determines “Return period” of earthquakes with specific magnitude. Some tables have been designed for studying Iran and the world earthquake.

If return period of a 7-Richter earthquake is one hundred years, for example. It means that an earthquake with the magnitude of 7 Richter scale may happen within a century.

Statistical survey of Iran Earthquakes

Some of the big cities of Iran are located near seismically active faults and a big earthquake some times strikes some part of Iran which causes many losses. Recent researches about seismicity of Iranian platue and return periods of earthquakes in Iran have resulted in very shocking results. For example, in the cities of Tehran, Tabriz, Neishabour, Qazvin, Kashan, Mashad and Shiraz where a devastative earthquake had been recorded, there has been no major seismic activity recently.

Return period of a damaging earthquake in Tehran is 150 years. Since major economic, cultural and political activities are concentrated in the city of Tehran, a large earthquake as the same magnitude of Tabas Earthquake in 1978 will cause many damages.

Ground Water

Spring flow changes just before an earthquake

Tension

When an earthquake is about to rupture, tension increases in the rocks of the active fault. These changes can be measured by tension meters.

Radio waves

In some cases, the antennas which had been installed to predict an earthquake, received some unusual signals.

One of the main steps in seismology is determining age of the seismic events. Having these ages, a better evaluation can be performed regarding the risk of earthquake in a region. Absolute and relative techniques are used to determine past earthquakes age.

1- Studying old trees: Some trees are damaged seriously by earthquakes and sometimes their roots cut.  Therefore mineral absorption of the roots deteriorates. It can be estimated when earthquake happened by counting the age rings of a tree and observing some thinner rings, if the tree is alive. Famine and volcanism have the same effect on trees.

2- Using Karstic structures: Stalaktic and Stalagmites are the most abundant Karstic structures which can be used for determining age of ancient earthquakes.

A Stalagmite structure is always beneath a Stalagmite structure and their formation is the same as each other relative to Lime layers without any discontinuity. If there is tectonic activity in the region because of fault activity, the axis of the formation of layers is not in the same direction and there will be some discontinuities in it. Observing displacement at the cross sections of this structure is an indication of an earthquake and the time its occurrence can be determined by C14 method.

3- Littoral lines:An earthquake will cause marginal terraces in margin of oceans and seas which are located in a higher height relative to the present shore. The number of there terraces is an indication of the number of earthquakes which have happened in the area.

Climate changes have the same effect which should be differenciated from the above factor.

Radon gas

Before the main rupture, rocks expand a little. This expansion is because of the many fractures and joints in the rock. This expansion causes P-wave velocity in the rock decreases but its electric conductivity and permeability increases. Radon gas in Uranium minerals escapes and its concentration increases in the springs.

Geomagnetism

Some authors have reported change in the gravity and magnetism field of the earth.

Electric conductivity

Measurable changes of electric conductivity of rocks decrease before the main shock.

Number of earthquakes

The number of minor shocks increases gradually but it decreases before the main shock suddenly.

Animal's reaction

Some of the animals such as dogs and horses behave strangely before an earthquake.