world's major observatories, particularly those in the United States, to the earthquake hazards in these

Protecting large telescopes from earthquakesRichard C. HaskellPresident, Tridis Engineers Inc.2304 Huntington Drive, San Marino, CA. 91108AbstractSince 1903 when good instrumented data first became available over 100 greatearthquakes of Richter Magnitude 8.0 or greater have occurred in the world. Manyof the high seismicity zones in the world are in locations of large astronomicalobservatories. These include Chile, California, Hawaii and Japan. When buildingnew observatories it is necessary to provide seismic protection in case anearthquake does occur. It is also important to reevaluate existing facilities todetermine if they are adequately protected according to the latest engineeringpractice.This paper relates the locations of the world's major observatories,particularly those in the United States, to the earthquake hazards in theseareas. Instances of damage to instruments during earthquakes will be numerated.Criteria for designing facilities to resist earthquake loads will be summarized,and certain protection techniques will be presented.IntroductionOn the morning of February 9, 1971 a large earthquake of Richter Magnitude6.6 shook the metropolitan area of Los Angeles, California. A 24" solartelescope was located on an isthmus in the center of Van Norman reservoir nearthe epicenter. The telescope was shaken off its pedestal supports and its vacuumsystem failed. Actuator screws on a spectroheliograph were damaged so badly theyhad to be returned to the factory for repair. Some time was lost until thefacility was back in full operation once again.In the summer of 1979 a small earthquake of Richter Magnitude 4.4 was feltin Big Bear, California. A crack appeared in the reinforced concrete piersupporting the solar telescope in the middle of Big Bear Lake, and the facilitywas down for three weeks while repairs were made.These are two examples of incidents where significant damage occurred totelescope facilities from earthquakes. A more thorough survey would probablyturn up many others. It is quite clear that observatory buildings and theircontents must in some way be protected from this hazard, particularly since mostof these facilities are designed for relatively long lives. Although it is notpossible to achieve 100% protection, it is usually possible to provide goodprotection against an earthquake that might reasonably be expected to occurduring the life of the structure. Quite often this protection is not expensive,particularly if it is incorporated into the original construction.Seismic risk around the worldA large earthquake can occur at any place in the world. However, there arecertain areas where earthquakes are more likely to occur. The earth's crust ismade up of a group of tectonic plates that move very slowly with respect to each