In our latest Japanese foreclosed property report we have added a great deal of information to assist you to avoid the damages caused by earthquakes. Japan is amongst the most unstable or active in the world, alongside places like Papua New Guinea and Indonesia. We also have a NZ property report, and since there was a recent serious earthquake in NZ, we thought we would offer some general public information to assist property buyers. I have some understanding on this issue since I studied geology and geophysics at university in Sydney.
There are some basic issues to understand:
1. Earthquake risks are not always understood because fault lines are not always know. This is because modern human records cover a far shorter period of time than geological processes. Active or previously 'inactive' fault zones can be concealed by recent sediment cover. This is true of the Kanto plain, as well as the Canterbury Plains of NZ.
2. Earthquakes can be zones of weakness, and perhaps not just a single plane of weakness. It might be better to consider them 'crimple zones'. They comprise jagged lines of weakness with zones of intense distortion as well as zones of dilation, where stresses vary from weak to intense depending on the competency of the rocks involved.
3. Earthquake risks are not equal for different regions. Competent basement or foundation rock provides greater security than loosely consolidated sediments. For this reason, thick piles of sediment pose greater risk
4. Unconsolidated sediments pose particular concerns where they are water-saturated, i.e. In areas of high rainfall or low-lying areas. In these cases, sentiments in the 'crimple zones' can undergo liquefaction, in which case they lose all strength and behave like a liquid. This can result in the foundations of your house sinking into the soil in the earthquake zone.
5. An earthquake zone can be a broadly-defined, as is required to relieve the stress. i.e. It is common for a transform fault like in NZ to involve multiple faults, with the outer faults defining the fault zone.
6. Those regions which were historically active for earthquakes might not adequately define zones of future vulnerability. For the reasons already mentioned, old zones of faulting might be concealed by extensive flood plains, as was the case with the Christchurch earthquakes in Sept 2010.
7. A serious earthquake can result in a large number of houses being heaved off their foundations, which are contorted by the ground movement. The houses can sink into the soil, and its common for any brittle structures to crack and fall into the house, i.e. In Christchurch, most brick houses in the fault zone were destroyed as they crack up. Chimneys made of brick often toppled into the structure, posing a risk to residents. Most of these houses need to be demolished and newly built, even if they look fine from the outside. The door hinges might not work properly because of the distortion, just as your car hinges can be poorly aligned after a car crash.
8. Different countries have differing levels of preparedness for coping with earthquakes. Japan is far better in this respect than NZ. Avoid brick homes in NZ, even though they have increased in popularity. The old weatherboard and modern galvanised sheet homes probably make the most sense. Houses on concrete pilings (i.e. posts) rather than concrete slabs make the most sense, though that ultimately depends on the thickness of the foundation, the size of the slab, the competency of the host rock, and the saturation of any unconsolidated sediments. Avoid low-lying areas with unconsolidated sediment foundation.
In the Japan report, I offer a map showing regions of vulnerability to earthquakes based on the Japanese governments analysis. For NZ, there is a transform fault going up the centre of the South Island, and up through Wellington to Hawkes Bay on the North Island. The Taupo Volcanic Zone has not historically been an area of intense earthquake activity, though it is active as well, since that zone is spreading apart at 10cm per year. There is a fault going down to Wanganui City (population 40,000). This region experienced a 5.1 earthquake in Aug 2010.
Author Andrew Sheldon Applied Critical Thinking | www.SheldonThinks.com