What maximum magnitude of earthquake can my house or building survive?
There is no direct relation between earthquake magnitude and damage it causes to a certain structure. The damage caused by an earthquake depends on numerous factors such as distance of epicenter to the structure in question, depth of the earthquake, soil conditions at the site of the structure, and design and construction quality of the structure. For example, an earthquake measuring 7.5 on the Richter scale but having epicenter 500 km away from the structure might be less damaging than an earthquake measuring 6 on the Richter scale but having epicenter only 10 km away from the structure.
Can we predict an earthquake?
No. However, upon studying the historical earthquake occurrence data and tectonic conditions at a location the probability of occurrence of an earthquake greater than certain magnitude in a defined time-period can be assessed to a considerable accuracy.
Suppose my house or building sustains some damage during an earthquake. How do I know if it is still inhabitable?
Usually after an earthquake surveys are conducted by structural engineers working for government or private organizations to assess and tag buildings or houses as immediately inhabitable, inhabitable upon repair or to be demolished and reconstructed.
Suppose my house or building sustains significant damage during an earthquake. Who will pay for the required repair or reconstruction?
In absence of any earthquake insurance, most likely the owner of the house would have to pay the costs. Similarly, in case of a building housing multiple families the cost would have to be borne by the residents or the building’s welfare association.
Is it a good idea to get earthquake insurance for my house or building?
Earthquake insurance being very popular or even compulsory in many countries is relatively rare in India. Some companies in India offer earthquake insurance as an add-on to fire insurance with fixed and minimal premiums throughout India. So, it might be a good idea to get such an earthquake insurance policy if you live in an area with high earthquake hazard. However if you are representative of a residents welfare society(RWA) looking to get an earthquake insurance policy for you building or entire society in India, the chances of you finding a suitable insurance policy meeting your requirements at an affordable premium are currently slim.
How do I know the seismic hazard in my area?
India has been divided into four seismic zones (II-V) of increasing severity (refer map below). Although being relatively approximate this division can provide a good estimate of relative seismic hazard in your area.
Seismic Zoning Map of India. Source : www.mapsofindia.com
Why is the seismic zoning map approximate?
This map is the result of collective wisdom of a panel of experts and considers factor such as population density, presence of buildings of national importance etc. It roughly divide India into four seismic zones. However, researchers (including us) have discovered during their research that the seismic hazard can differ by a factor of more than 2.5 between two areas assigned the same seismic zone.
How do I know the exact seismic hazard in my area?
A probabilistic site-specific hazard assessment could be done to assess the seismic hazard at any site and quantify the uncertainties involved to a considerable accuracy. Such a study is, however, offered by relatively few institutions or companies and one should carefully scrutinize their credentials before employing them to do such a study to insurance accuracy and technical basis of the results.
Will my earthquake insurance premium depend on the seismic hazard at my site?
Ideally, it should. However currently, insurance companies in India do not vary their premiums based on any scientific study. Presently insurance companies vary the premium based on your seismic zone. Some might even offer a flat premium throughout India.
Is wind more damaging to buildings than earthquakes?
Not exactly. To understand this, we must recognize the nature of wind and earth loading applied on buildings during their design. Buildings in India are designed for full force of expected wind load for 50 years return period (highest wind speed expected during 50 years). However, to be economical and practical, buildings are designed for a fraction (10 %-15%) of expected earthquake load during 2500 years return period (maximum earthquake expected during 2500 years). Therefore, for such a large and rare earthquake buildings are expected to undergo serious structural damage but save lives of its occupants. On the other hand, buildings are expected to bear large windstorms without any structural damage. It is very rare for a building to sustain structural damage during high winds, which are much more frequent than large earthquakes.
The design wind load exceeds the design earthquake load for buildings having more than 25-35 story (depending on the location). The higher loading value sometimes makes structural engineers believe that, for their building, wind is more damaging than earthquakes. However, in worst case, a large storm might make you very uncomfortable (due to floor vibrations) but will not structurally damage your building. But a large earthquake can cause severe injuries to the occupants and considerable structural damage in buildings (even make them inhabitable).
