Tiltmeter evaluation of the LMT/GTM azimuth track following the earthquake of September 2017

Following the magnitude 7.1 earthquake in central Mexico on 19 September 2017, personnel from the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT/GTM) performed a visual inspection of the foundation and structure of the LMT/GTM. Though no damage was found, the project also conducted a measurement of the system using the precision tiltmeters that are permanently installed at the elevation axis. Fortunately, a series of baseline tests had been run in 2013 after the installation of the first tiltmeter, including a comparison to the original survey results. To match the fastest of these tests, the site crew ran the telescope through ±360° of azimuth rotation at moderate slew speeds in each direction. The most important result is that there have been no statistically significant changes in the tilt variation of the alidade since either the original track surveys during initial construction or the tiltmeter tests in 2013. This conclusion is based on comparisons of tilt results averaged over 2 degree bins in the data. The result confirms that there was no apparent change to system performance.