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= Hz p at 50 mHz and a translational coupling of less than 1 μrad=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 fromM 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.