Quantifying The Quality Of PBO Borehole Strainmeter Data

UNAVCO operates a network of 75 borehole strainmeter as part of the Plate Boundary Observatory (PBO), the geodetic component of the Earthscope program. The quality of the borehole strainmeter data is monitored both to inform UNAVCO's field engineers of possible instrument problems and to convey to the community the level of confidence they can have in recorded signals when they incorporate the data into geophysical models. In this presentation we describe the metrics developed to track data quality and show how the results have varied since completion of the network in October 2008. The metrics are designed to assess performance across the broad range of frequencies over which a strainmeter operates: the ability to record teleseisms, the signal to noise ratio in the tidal bands, the state of compression of the borehole and the presence of offsets in the time series. Strainmeters are designed to have optimal performance at periods of minutes to days, their purpose in PBO is to provide a temporal and spatial resolution of strain transients that cannot be obtained with GPS or seismology. Embedded within a network of over 1100 continuously operating GPS sites and collocated with seismometers, the strainmeter network completes the spectrum of plate boundary deformation signals that PBO can detect. We will explore the application of techniques now standard for seismic data, power spectral density analysis, to the strain data set. Creating a spectral fingerprint for each instrument could allow identification of changes in site characteristics and enable researchers to select strainmeters that are good candidates for detecting particular strain events such as aseismic creep or Episodic Tremor and Slip strain pulses.