superadobe structures have withstood earthquakes as severe as 7.2 magnitude. Methodology Superadobe's earthbag technique lends itself to a wide range of materials. Polypropylene tubing is ideal, although burlap is also sufficient. Likewise, while sand, cement or lime are preferred, virtually any fill material (e.g. gravel, crushed volcanic rock or rice hulls) will work. After materials are gathered and the dimensions of the building are decided upon, a circular foundation trench is dug, approximately 1 foot deep and 8–14 feet in diameter, giving room for at least two layers of earthbags to be laid down underground. A chain is anchored to the ground in the center of the circle and used as a pair of compasses to trace the shape of the base. Another chain is fastened just outside the dome wall: this is the fixed or height guide and provides an interior measurement for the layers as they corbel higher, ensuring the accuracy of each new layer as it is laid and tamped. Between layers of tamped, filled tubes, loop of barbed wire functions as mortar and holds the structure together. Window voids can be placed in several ways: either by rolling the filled tube back on itself around a circular plug (forming an arched header) or by sawing out a Gothic or pointed arch void after the filler material has set. Once the corbelled dome is complete, it can be covered in several different kinds of exterior treatments, both for aesthetic reasons and to protect the structure from environmental damage such as that from ultraviolet radiation. Like the materials for the construction itself, there are multiple choices. While CalEarth names plaster as the most common finishing option, soil and living grass have also been used. Khalili has also used a mix of earth and plaster, further covered by a "reptile" layer of cement and earth balls that strengthen the finish by redirecting stress. Emergency shelters According to Khalili's website, in an emergency, impermanent shelters can be built with unskilled labor, using only dirt with no cement or lime, and for the sake of speed of construction, windows can be punched out later due to the strength of the compressive nature of the dome/beehive. Superadobe is not an exact art and similar materials may be substituted if the most ideal ones are not readily available. Ordinary sand bags can also be used to form the dome if no Superadobe tubes