Improving the Robustness of the Advanced LIGO Detectors to Earthquakes

TL;DR

The paper introduces EQ mode, a control scheme that enhances Advanced LIGO's ability to operate during earthquakes by reducing seismic disturbances and maintaining interferometer stability, thus improving robustness against high ground motion.

Contribution

The paper presents a novel global control scheme, EQ mode, that automates seismic isolation during earthquakes, significantly improving LIGO's operational robustness under extreme ground motion conditions.

Findings

Enhanced detector operation during earthquakes with ground velocities up to 3.9 μm/s rms.

Reduction of differential motion of interferometer arms during seismic events.

Set a new record for seismic control performance in Advanced LIGO.

Abstract

Teleseismic, or distant, earthquakes regularly disrupt the operation of ground--based gravitational wave detectors such as Advanced LIGO. Here, we present \emph{EQ mode}, a new global control scheme, consisting of an automated sequence of optimized control filters that reduces and coordinates the motion of the seismic isolation platforms during earthquakes. This, in turn, suppresses the differential motion of the interferometer arms with respect to one another, resulting in a reduction of DARM signal at frequencies below 100\,mHz. Our method greatly improved the interferometers' capability to remain operational during earthquakes, with ground velocities up to 3.9\,$\mu \mbox{m/s}$ rms in the beam direction, setting a new record for both detectors. This sets a milestone in seismic controls of the Advanced LIGO detectors' ability to manage high ground motion induced by earthquakes, opening a path for further robust operation in other extreme environmental conditions.