Quantifying Earthquake-Mode Performance and Lock Survival in Advanced LIGO

The Advanced LIGO detectors must maintain maximum sensitivity during observations, but earthquakes and elevated ground motion threaten the low-noise interferometer lock state. To protect against this, LIGO uses an Earthquake Mode (EQ-mode) that modifies seismic isolation when ground motion exceeds ~400 nm/s. Quantifying how effectively EQ-mode preserves lock ultimately maximizes observing time which has been difficult with previous Guardian-based methods.

We present an automated framework that evaluates EQ-mode performance daily, weekly, and monthly by analyzing weekly episodes of engagement. The pipeline tracks transitions between nominal operation, EQ-mode activation, and recovery, classifying each event as a lock loss or survival. The framework outputs survival statistics, ROC curves, and correlations between seismic amplitude and lock retention, revealing optimal activation thresholds that balance protection and duty cycle. Preliminary results indicate the 400 nm/s threshold may be lowered to improve observing efficiency. This reproducible, detector-agnostic approach enhances LIGO’s science uptime and extends to Virgo and KAGRA