MENLO PARK, California (Reuters) - At every corner, the San Francisco area is commemorating the 100th anniversary of the April 18, 1906, earthquake that marked one of the worst natural disasters in U.S. history. A small band of aged survivors are making public appearances, including at the start of a recent baseball game. Museums and public halls are holding retrospectives, and construction and insurance companies are promoting their services against future earthquakes. The city has staged a new ballet titled "Earthquake" which includes sounds of seismic movements amid a sculpture producers say represents the Richter scale. Phones are ringing at...