Why might buildings in reclaimed areas be more dangerous than ones which are not during an earthquake?

Answer 1

Reclamation usually involves construction on areas that ere previously below sea level. Either the ground level is built up by the tipping of rockfill or berms are created and the water removed by pumping to create an area of dry land that is below sea level (this is a very common process in Holland).

The problem with this is that the amplitude of seismic waves is related to the ground through which they travel. The amplitude of seismic waves in poorly compacted sediments (such as those likely to be found in reclaimed areas) tends to be larger than that which would occur where the founding material was stiffer and stronger (e.g. areas founded on bedrock). As such for a given earthquake, buildings in areas that are reclaimed are likely to experience more severe ground shaking than in other areas making them more likely to collapse.

Further to this, sediments can undergo a process known as liquefaction where the pore water pressure is driven up to such a high level the individual soil grains effectively become buoyant and the soil loses it's ability to support surface loads which can also lead to buildings collapsing.

Finally areas of reclaimed land that are still below sea level or are near the coast will inherently be at greater risk from a tsunami than other areas.

For more information on this, please see the related questions.

Answer 2

Buildings in reclaimed areas may be more susceptible to liquefaction, where the soil loses its strength and behaves like a liquid during an earthquake. This can cause buildings to sink, tilt, or even collapse. Additionally, reclaimed land is often more vulnerable to ground shaking due to the softer soils and fill material used in the construction process.