Low Frequency Tilt Seismology with a Precision Ground Rotation Sensor

TL;DR

This paper demonstrates the use of a high-precision ground rotation sensor at LIGO Hanford to measure teleseismic surface wave rotations, providing new insights into seismic wave phase dispersion with high sensitivity.

Contribution

It introduces a novel, translation-free method for measuring small ground rotations using an inertial sensor with extremely low noise at low frequencies.

Findings

Sensor achieved 0.4 nrad/√Hz noise floor at 50 mHz

Rotational measurements agree with traditional seismometer array results

Successful estimation of phase dispersion curves from rotational data

Abstract

We describe measurements of the rotational component of teleseismic surface waves using an inertial high-precision ground-rotation-sensor installed at the LIGO Hanford Observatory (LHO). The sensor has a noise floor of 0.4 nrad$/ \sqrt{\rm Hz}$ at 50 mHz and a translational coupling of less than 1 $\mu$rad/m enabling translation-free measurement of small rotations. We present observations of the rotational motion from Rayleigh waves of six teleseismic events from varied locations and with magnitudes ranging from M6.7 to M7.9. These events were used to estimate phase dispersion curves which shows agreement with a similar analysis done with an array of three STS-2 seismometers also located at LHO.