Protecting a fragile giant: seismic design, analysis, results and requirements for the GMT

The primary mirror of the Giant Magellan Telescope (GMT) consists of seven 8.4-meter diameter borosilicate segments. While this design has optical advantages, the unmitigated seismic risk is significant. Recently added design features meet this challenge. A 2D seismic isolation system decouples the telescope from horizontal ground motion and dampers at the interface with the primary mirror segments attenuate their motion. A detailed analysis framework has been developed to justify and refine the design. Discrete analyses, in which the models are exercised at discrete seismic intensity levels, are used to generate requirements throughout the telescope via a seismic response spectrum approach. Risk-based analyses utilize a broad characterization of uncertainty to assess probability of survival of the most critical components. These tools support a general design strategy that effectively trades the cost of designing and constructing the telescope against the seismic risk.