EARTHQUAKE PREDICTABILITY RISES AS SEISMOLOGISTS REALIZE THAT FORESHOCKS ON SOME FAULTS PRE-ANNOUNCE STRONGER QUAKES.

 

photo: NBC 

One of the phenomena that man has not been able to harness or at least to glean enough information to formulate predictions from, is the occurrence of earthquake.  We know why and where and how, but not when.

In some cases however, seismologists are now realizing that some tell tale clues might be offered by foreshocks, in formulating the size and timing of the main quake.

Foreshocks of course, are smaller quakes hat strike sometimes only a few hours before a quake or even a week ahead of time and they are usually significantly smaller in intensity than the real event.  

Not all quakes have foreshocks, but when they did, until now, they did not offer any important clues as to what was in store. 

New studies of plate boundaries have revealed that foreshocks arise from the slow creeping movement that precede the strong event.  

As the fault boundaries creep, the smaller zones that resist movement create small breaks that generate the foreshocks.   Foreshocks do not cause the actual main temblor, they just precede the greater snap that causes the actual earthquake.   Studying the foreshocks therefore, can only help in understanding what comes after them.  

Studying earthquakes of magnitude 6.5 or higher that occurred along the Pacific Ocean rim, where different countries at very long distances capture seismic waves in their monitoring networks scientists realized that half of the earthquakes that occurred between 1999 and 2011, occurred on plate boundaries and half were intraplate occurrences. 

On average, seismic events along faults was nearly constant for 60 days before the main seismic event, when small foreshocks started to register.  About 20 days before the main temblor struck, the foreshocks became more pronounced and contined accellerating about 48 before the event, and then again 2 hours before the event.  

This has led scientists to believe slow slippage begins well before the main temblor occurs.  This initial phase, called the nucleation phase, could help seismologist predict quakes in the future.  

In intraplates quakes, instead there are usually no foreshocks, due to the different geological nature of the area where the temblor occurs.  

More research will be done to understand what the foreshock pattern is in other earthquake zones around the world.  

Source : NBC 3.25.13