Seismic defence structures

1. A seismic wave shield comprising a set of at least two rows of columns, the at least two rows of columns being spaced apart from each other and embedded in regolith, wherein the Young's modulus of the material forming the columns is at least 10 times higher than the Young's modulus of the regolith and wherein the columns are positioned on points of a hexagonal, or other Bravais, lattice and are in contact with and clamped to bedrock to form a stop band for blocking seismic waves, with a zero or near zero lower frequency limit, wherein there is a material contrast between a material forming the columns and the regolith, and further wherein the seismic wave shield is positioned outside of and away from a lateral perimeter of a building, wherein a width of the shield in a direction of waves to be blocked is defined by the at least two rows of columns, and wherein a total volume of the columns is at least 15% of the volume of the seismic wave shield.

2. A seismic wave shield according to claim 1 wherein the material forming the columns has a higher density than the regolith.

3. A seismic wave shield according to claim 1 wherein a bottom portion of each of the columns is embedded in the bedrock.

4. A seismic wave shield according to claim 3 wherein columns are embedded in the bedrock by more than 0.3 m.

5. A seismic wave shield according to claim 1 wherein the material forming the columns is at least 1.1 times as dense as the regolith.

6. A seismic wave shield according to claim 1 wherein the columns are positioned periodically or near periodically in the seismic wave shield.

7. A seismic wave shield according to claim 1 wherein a width of the shield in a direction of waves to be blocked is greater than two rows of columns.

8. A seismic wave shield according to claim 1 further comprising a plate attached at a first end of the plate to a first column of the seismic wave shield, the plate further being attached at a second end of the plate to a second column of the seismic wave shield.

9. A seismic wave shield according to claim 1 wherein at least one of the columns comprise concrete.

10. A seismic wave shield according to claim 1 wherein at least one of the columns comprises steel and concrete.

11. A seismic wave shield according to claim 10 , wherein the at least one of the columns is made up of layers of concrete and layers of steel which alternate vertically up the column.

12. A seismic wave shield according to claim 10 , wherein the at least one of the columns is made up of concentric circle sections of concrete and steel.

13. A seismic wave shield according to claim 10 , wherein the at least one of the columns is formed of a sleeve of steel surrounding a column of concrete.

14. A seismic wave shield according to claim 1 , wherein the total volume of the columns as a fraction of the volume of the seismic wave shield varies across the seismic wave shield.

15. A seismic wave shield according to claim 14 , wherein a part of the seismic wave shield most exposed to the waves has a higher total volume of the columns as a fraction of the volume of the seismic wave shield and a part of the seismic wave shield least exposed to the waves has a lower total volume of the columns as a fraction of the volume of the seismic wave shield.

16. A seismic wave shield according to claim 1 , wherein the distance between the centers of neighboring columns is at least twice the diameter of the columns.

17. A seismic wave shield according to claim 1 , wherein the distance between the centers of neighboring columns is 10 to 100 times smaller than a wavelength of seismic waves which are blocked by the seismic wave shield.

18. A method of shielding an area from seismic waves by installing a seismic wave shield according to claim 1 on at least a part of a perimeter of the area.

19. A seismically shielded building comprising a seismic wave shield according to claim 1 positioned adjacent to a part of a perimeter of a building and outside of said perimeter.