Low‐Frequency Tilt Seismology with a Precision Ground‐Rotation Sensor

We describe measurements of the rotational component of teleseismic surface waves using an inertial high-precision ground-rotation sensor installed at the Laser Interferometer Gravitational-Wave Observatory (LIGO) Hanford Observatory (LHO). The sensor has a noise floor of 0: 4 nrad/root 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 M 6.7 to 7.9. These events were used to estimate phase dispersion curves that show agreement with a similar analysis done with an array of three STS-2 seismometers also located at LHO.