TEHRAN - A meaningful earthquake prediction must clearly define the time, location, and magnitude of a future event. Short-term earthquake prediction—that is, the ability to issue warnings from minutes to months before a main shock—is impossible without visible and practical foreshock monitoring. Therefore, a key goal is to discover the precursor faulting process that can tell us where, when, and how big an impending earthquake will be.

In the region around the megacity of Tehran, the active faults are responsible for several large-magnitude historical (pre–1900) earthquakes as well as the current seismicity. This situation imposes a high seismic hazard on this megacity. Important recorded historical earthquakes in Tehran include 312–280 BC, Ms7.6, Rey; 743 AD, Ms7.2, Garmsar; 855 AD, Ms7.1,  Rey; 958 AD, Ms7.7, Taleghan; 1177 AD, Ms7.2,  Karaj; 1608 AD, Ms7.6, Taleghan; 1665 AD, Ms6.5, Damavand; 1830 AD, Ms7.1, Damavand events.

Prediction of a possible major earthquake is a major task force for disaster risk reduction in Iran. Repeated geodetic measurements associated with severe seismic events with the intensive development of Global Navigation Satellite Systems (GNSS) in recent decades have made earthquake prediction research more effective. 

The results of GNSS observations in the epicentral zone of the three large Napa earthquakes in northern California with a magnitude of M6.1 in 2014; the Baja California Earthquake with a magnitude of M7.2, in 2010; and the Parkfield California earthquake with a magnitude of M6.0 in 2004 is obtained by examining the deformation characteristics of the ground surface before, during and after the earthquake. 

The results prove the existence of unusual deformations near the epicenter of earthquakes. Changes such as ground swelling and shear strain are indicated by the deformation of the ground surface in the epicenter of the earthquake from months to years before the main shock. The revealed heterogeneities can be considered as deformation indicators of severe earthquakes. According to the historical data, and the current detailed research, the values of critical deformations should be determined more accurately so that it is possible to produce warnings and announce earthquake predictions in this way.

A new study by researchers from the French National Institute for Sustainable Development, using GPS satellites and thousands of geodetic stations for analysis, showed that these earthquakes have a pre-slip fault phase that can extend earthquake warning systems from minutes to hours in advance. 

The method of study was the systematic analysis of earthquakes based on horizontal position changes of approximately 3000 geodetic stations measured using the Global Positioning System (GPS) near 90 earthquakes with a magnitude greater than 7.

 In the earthquake predictors studies, researchers found a pattern by examining detailed GPS data for geographic areas around the epicenter of earthquakes. It was observed that the sliding between the tectonic plates caused the earth to move in a measurable direction in the horizontal direction. The horizontal motions of the stations accelerate exponentially in a direction consistent with the slow slip of the fault near the rupture initiation point of the earthquake fault in the 2 hours before the earthquake rupture.

These slips can be observed and measured using GPS. It has been determined that these slips occurred two hours before the earthquake, and on the other hand, these movements are too small to be recorded in standard seismographs and are usually not recorded and announced. Most importantly, the researchers observed the same slip in all the earthquakes studied.

This work shows that a reliable earthquake system can be designed based on an accurate GPS monitoring system. More work is needed to prove that such a forecast exists for all, or most, large earthquakes. Also, some upgrades in GPS technology are needed to allow for the measurement of events around the clock.

The GPS time series preceding these 90 different magnitude 7 earthquakes show a subtle leading signal that is louder, and therefore detectable, than the noise about 2 hours before the occurrence of these large earthquakes. This may enable fault monitoring at this stage and on this type of indicator with more accurate and denser tools. The presence of a background phase of slip on the fault prior to major earthquakes was found by measuring 3026 high-displacement GPS time series predicting displacement on the expected directions of foreslip at the epicenter. Such a prediction can be called the "preliminary stage of fault slip two hours before the main seismic rupture".

A major event begins with a process called "earthquake nucleation". If it can be confirmed that the initiation of earthquake rupture often involves an initial phase of several hours, a tool can be developed to reliably measure it, and issue a pre-warning, informing the public that rupture is imminent.

These slips are too small to show up on seismographs, but they can—if detected—using geodesy to indicate when an earthquake started. Such an approach has been tested before, but previous research has only looked at a small number of earthquakes and produced warning signs that would be seen in the absence of an earthquake.

According to such research on earthquakes with a magnitude greater than 7, gradual, slow, and usually - so far - undetectable slip between tectonic plates begins about 2 hours before the earthquake. The noise levels of current GPS sensors make deformation detection possible only in large data sets. This requires GPS sensors capable of detecting movements with an accuracy of 0.1 mm.

In the past, there have been many retrospective observations of various types of earthquake foreshocks – aftershocks, deformations, etc. If we make significant progress in measurements - or sensor sensitivity improves, with more of them - we can find more hope in earthquake prediction.

It should be noted that carrying out such monitoring for our country requires investment at the national level. For example, to install 30 observation stations in the Tehran region alone, a national investment is needed.  The technical knowledge of installing and operating such a system is available in the country's organizations and in universities and colleges.