  The Tokai Strainmeter Network (TSN), a dense network deployed in the Tokai
region, which is the easternmost region of the Nankai trough, has been designed
to monitor slow slips that reflect changes in the coupling state of the plate
boundary. It is important to evaluate the current capability of TSN to detect
and locate slow slips. For this purpose, the probability-based magnitude of
completeness developed for seismic networks was modified to be applicable to
the evaluation of TSN's performance. Using 35 slow slips having moment
magnitudes M5.1-5.8 recorded by TSN in 2012-2016, this study shows that the
probability that TSN detected and located a M5-class slow slip is high (> 0.9)
when considering a region in and around the TSN. The probability has been found
to depend on the slip duration, especially for M5.5 or larger, namely the
longer the duration, the lower the probability. A possible use of this method
to assess the network's performance for cases where virtual stations are added
to the existing network was explored. The use of this application when devising
a strategic plan of the TSN to extend its coverage westwards is proposed. This
extension that allows TSN to cover the entire eastern half of the Nankai trough
is important, because the historical records show that the eastern half of this
trough tends to rupture first.
