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A Rotational Seismometer for Geohazards and Scientific Monitoring in a Regional Seismic Network (Rsn)

Description: 

Observing seismic rotations of the ground and structures is a challenge at the advancing forefront of seismological monitoring. Incorporating ground rotations into monitoring at a regional scale fuels research and development of both instrumentation and theory. Combining pure point rotations and translational shaking at a site comprise a “6 degree of freedom” (6DoF) “mini-array”. 6DoF observations can be used to infer the velocity profile at the site, help locate off-array events, and refine S-wave arrivals. Moreover, they contain information about inhomogeneity, anisotropy, near-field effects, structural damage, and phase conversions. And because rotations may contaminate translational sensors, they can help correct and reduce noise on traditional sensors. An RSN can use rotations in several settings to assist and enhance their missions. A critical goal currently of the RS effort is to measure pure wide-band rotations at the low-noise spectral model level. We have field-tested a new portable rotational motion sensor, the QRS quartz rotational seismometer. The QRS uses a load-sensitive resonant quartz crystal to measure the rotational torque sensed by a beam-balance angular accelerometer, providing inherently digital broadband observations of pure rotation. The combination provides improved insensitivity to translational motions and a lower noise floor than other similar-sized systems currently employed. During a 3-month long deployment of a QRS alongside a broadband seismometer in a quiet vault, we observed rotational and translational motions from several small (M<3) local and regional earthquakes as well as longer-period waves from large teleseisms. The noise floor was measured to be ~45 pico-radian/Hz^-1/2 at 1 Hz and ~23 pico-radians/Hz^-1/2 at 0.1 Hz, the sensor’s resonant frequency. Among other similar-sized broadband rotation sensors this represents a lowering of the instrumental noise floor by more than two orders of magnitude.

Session: Network Seismology: Recent Developments, Challenges and Lessons Learned [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Paul Bodin

Student Presenter: No

Invited Presentation: 

Authors