While it is common knowledge that a large earthquake is followed by aftershocks, most of the residents of Christchurch and Canterbury had no idea of the practical implications of this. With over 1500 aftershocks shaking the area since the 4th September earthquake, many people have been left anxious and stressed by their frequency and intensity.
Prediction of Strong Aftershocks to Continue in Christchurch
The Weekend Press reported on Saturday October 16th, that further aftershocks of 5.0 or higher are possible in the next few weeks. Canterbury University doctoral student, John Holdaway told The Weekend Press that the Christchurch region had not gone for more than 5 ½ days since the main earthquake without at least one 4.3 plus magnitude earthquake. He predicted that this pattern looks set to continue with at least one large aftershock occurring every two to five days over the next few weeks.
Holdaway also compared the total energy released by the aftershocks to the energy released by the Haiti earthquake. He stated that the Haiti aftershocks released about 245 trillion joules of energy in the first 18 days after the main earthquake. By comparison, the Canterbury aftershocks have only released 85 trillion joules. He warned that his graphs predicted that at least another five to ten trillion joules of energy still needed to be released. This amount is equivalent to one 5.5 magnitude aftershock or four 5.1 aftershocks.
Aftershocks cause Stress to Christchurch Residents
Although the residents of Canterbury have lived through over 1500 aftershocks, they still find them stressful. Many say the unpredictable occurrence makes them even more difficult to handle. There is no pattern to the aftershocks and hours may pass without any occurring, followed by a cluster of two or three within a short space of time.
While most of the aftershocks have not caused damage, those with a magnitude of over 4.0 have potential to harm. Many of the brick buildings in the CBD have suffered further damage through the aftershocks of over 5.0. Residential homes have also deteriorated with cracks widening and windows shattering.
What do the Aftershocks Feel Like
The intensity of the aftershocks depends on their depth and distance from Christchurch. Geonet has a real time reporting system that supplies this information.
The tremors normally start with a trembling sensation that intensifies into shaking. Those with a magnitude of 4.0 and above are often accompanied by banging and noise as houses and buildings vibrate. The stronger aftershocks may knock bottles and ornaments over and cause pictures on the walls to tilt. Their duration is normally measured in seconds. Many residents have reported that they are woken regularly by the shakes and tremors.
Experts have predicted that strong aftershocks are to be expected for the next few weeks or even months in Christchurch and Canterbury. While this is a normal follow-up to a large earthquake, residents are stressed and tired by the ongoing shakes. The aftershocks also have the potential to cause further damage.
Debbie Roome - Debbie Roome is an award-winning freelance writer, journalist and novelist with over 25 years experience.
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