Observations of Rotational Motions from Local Earthquakes Using Two Temporary Portable Sensors in Waynoka, Oklahoma.

Characterizing rotational motions from earthquakes at local distances has the potential to improve earthquake engineering and seismic gradiometry by better characterizing the complete seismic wavefield. Applied Technology Associates (ATA) has developed a proto-seismic magnetohydrodynamic (SMHD) three-component rotational rate sensor. We deploy two ATA rotational rate sensors at a temporary aftershock station in Waynoka, Oklahoma. From 27 April to 6 June 2017, we recorded the translational and rotational motions of 155 earthquakes of M_L≥2.0 within 220 km of the station. Using the recorded events, we compare peak ground rotation rate (PGω˙) with peak ground velocity (PGV) and with peak ground acceleration (PGA). Our results support previously identified potential relationships between the two quantities. We also compare peak ground rotations (PGω) as a function of seismic moment and distance. We found that PGω˙ decays with an exponent of approximately -4.0 km^-1 for both horizontal and vertical components. On the other hand, PGA decays with an exponent of approximately -1.8 km^-1 for all components. We compute apparent phase velocity directly from the rotational data for both horizontally polarized shear waves (SH; 379 m/s with a standard deviation of 114 m/s) and vertically polarized compression and shear waves (P-SV; 387 m/s with a standard deviation of 121 m/s). Finally, by comparing various rotational and translational components, we look at potential implications for estimating local event source parameters. We found that the absolute correlation of nearby earthquakes decays at a rate of approximately 0.39/km for rotational sensors. This decay rate of absolute correlation is faster on translational sensors with a decay rate of 0.44/km. The latter may help in identifying phenomena such as repeating earthquakes by using differences in correlations as a function of distance and how these differences compare with translational correlations. [ABSTRACT FROM AUTHOR]