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Frequent, low-latency measurements of the Earth's rotation phase, UT1$-$UTC,critically support the current estimate and short-term prediction of thishighly variable Earth Orientation Parameter (EOP). Very Long BaselineInterferometry (VLBI) Intensive sessions provide the required data. However,the Intensive UT1$-$UTC measurement accuracy depends on the accuracy ofnumerous models, including the VLBI station position. Intensives observed withthe Maunakea (Mk) and Pie Town (Pt) stations of the Very Long Baseline Array(VLBA) illustrate how a geologic event (i.e., the $M_w$ 6.9 Hawai`i Earthquakeof May 4th, 2018) can cause a station displacement and an associated offset inthe values of UT1$-$UTC measured by that baseline, rendering the data from theseries useless until it is corrected. Using the non-parametric Nadaraya-Watsonestimator to smooth the measured UT1$-$UTC values before and after theearthquake, we calculate the offset in the measurement to be 75.7 $\pm$ 4.6$\mu$s. Analysis of the sensitivity of the Mk-Pt baseline's UT1$-$UTCmeasurement to station position changes shows that the measured offset isconsistent with the 67.2 $\pm$ 5.9 $\mu$s expected offset based on the 12.4$\pm$ 0.6 mm total coseismic displacement of the Maunakea VLBA stationdetermined from the displacement of the co-located global navigation satellitesystem (GNSS) station. GNSS station position information is known with alatency on the order of tens of hours, and thus can be used to correct the apriori position model of a co-located VLBI station such that it can continue toprovide accurate measurements of the critical EOP UT1$-$UTC as part ofIntensive sessions. The VLBI station position model would likely not be updatedfor several months. This contrast highlights the benefit of co-located GNSS andVLBI stations in support of the monitoring of UT1$-$UTC with single baselineIntensives. Abridged.

The Importance of Co-located VLBI Intensive Stations and GNSS Receivers:  A case study of the Maunakea VLBI and GNSS stations during the 2018 Hawai`i  earthquake