in
Iran. URM structures are vulnerable to collapse in an
earthquake. One problem is that most
mortar used to hold bricks together is not strong enough to survive the vibrations without cracking. In
California, the
1933 Long Beach earthquake resulted in a near-immediate statewide ban on construction of new unreinforced masonry school buildings and the
Field Act. A State law enacted in 1986 required
seismic retrofitting of existing structures. Retrofits are relatively expensive, and may include the building being tied to its foundation, tying building elements (such as roof and walls) to each other so that the building moves as a single unit rather than creating internal shears during an earthquake, attaching walls more securely to underlying supports so that they do not buckle and collapse, and bracing or removing
parapets and other unsecured decorative elements. Retrofits are generally intended to prevent injury and death to people, but not to protect the building itself. and as of 2008, most (but not all) of the unreinforced masonry buildings in
San Francisco have undergone retrofitting. There is particular cause for concern in regions which can generate strong earthquakes, but only rarely. Such regions may not have regulations limiting the construction of UMBs, or have only implemented them recently. Public awareness of earthquake safety may be low. For example, the
Wasatch Fault in the U.S. state of
Utah closely parallels the state's most populous metropolitan area, the
Wasatch Front (which includes the state capital
Salt Lake City). The Wasatch Front has a population of 2 million, and contains 200,000 UMBs compared with the entire state of California's 25,000. Utah has recently retrofitted many public UMBs to better withstand earthquakes, but most UMBs in the state are private homes. The lack of earthquake codes preventing the construction of UMBs was a major factor in the high death toll in the
2010 Haiti earthquake. ==See also==