Cascadia 120 Slim Posthole: A Combined Strong and Weak Motion Sensor for Early Warning and Regional Networks

Existing regional and EEW networks can be improved in data quality, providing more stations with unclipped continuous waveform observations and a uniform magnitude of completeness (Mc).  This is possible using upgraded deeper sensor emplacements and new instrumentation, based on a current understanding of system noise and updated equipment available today.  Station density is increasing with the EEW buildout, with a focus on minimizing latency, which also presents an opportunity to improve data quality for weak motion.  Mc and signal-to-noise ratio across the seismic and geodetic spectrum will be important for future OEF challenges and for hazard and science efforts such as 4D studies and the high resolution geophysical imaging of deep Earth structure.  Recent development of network Mc simulation code (Wilson et al., 2021) can be used to plan new networks, or infill stations to economically upgrade existing networks to these new best practices.  

An instrument system that provides high-gain weak motion data in precise alignment with strong motion data allows combined processing to create a seamless data set with maximum dynamic range.  The Nanometrics Cascadia 120 Slim Posthole has been designed to meet these requirements. Both weak and strong motion sensors are integrated in a single case which enables lowest system noise, unclipped observations, and precise coherence of signals between the weak and strong motion channels.  Cascadia 120 Slim and Cascadia Compact are deployed in networks now and we will present data showing the noise floor for weak motion, a seamless transition to strong motion, and high coherence between the two sensors for mid-sized events.

Authors: Valarie Hamilton, Geoffrey Bainbridge, Tim Parker, Daniela Wuthrich