Geology And Geophysics

Can one Earthquake cause another



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Even with the advanced technology of the 21st century there is still no way to predict when an earthquake will occur, only where they are most likely to occur. All is not lost however. A developing theory known in the scientific community as the stress-triggering theory may hold the key to identifying what areas will be most likely to experience seismic activity in the near future after a nearby earthquake occurs.

Ross Stein, in an interview with National Geographic, states "Generally a rupture will reduce the stress in a fault that is ruptured, but will increase it in other places. All other things being equal, we'll get more seismicity in those places." While this theory may not be of much help in areas that are deemed low hazard states such as Florida or Texas, it has the potential to become a highly useful tool in states such as California which are always at high risk for seismic activity.

The stress-triggering theory first began to develop after the 7.3 magnitude Landers, California earthquake in June of 1992. Prior to the Landers earthquake incident aftershocks were generally thought to occur only along the same fault line as the original earthquake. Just over three hours later however a 6.5 magnitude earthquake struck Big Bear, California which is approximately 25 miles from Landers on a completely different fault line.

While the three hour time difference between the California earthquakes is a somewhat extreme example there have been several other cases worldwide that give credence to the stress-triggering theory. For example, the great San Francisco earthquake of 1906 is now thought to have caused a lesser known, yet still violent, earthquake in California’s Imperial Valley less than a day later. More recently a 2004 earthquake in Indonesia (magnitude 9.1) is thought to have caused an 8.7 quake in March of the following year.

It should be noted that in accordance with this same theory there are some instances when one earthquake may actually decrease stress on a neighboring fault. The orientation of a fault, north-south or east-west for example, affects how that fault responds to stress from a nearby seismic event. If the fault is of the same orientation as the fault where the initial earthquake then stress increases as previously described. If the fault is at the opposite orientation the stress may have no effect at all or in some cases even lengthen the time before the next earthquake. While this occurrence is less common it is still a very important factor in trying to predict where and when an earthquake may occur.  

Even though it does not allow scientists to pinpoint the exact time an earthquake will occur the stress-triggering theory can help with disaster readiness. The ability to make the general public aware of a potential earthquake in the near future can give them time to buy the necessary supplies, protect their belongings and review any emergency plans they may have in place with their family or co-workers. With further research it has the potential to save many lives world-wide.

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