# Responses of Water Temperature and Level to Large Earthquakes in Tibet
## 2 Data Selection and Methods  
In this study, we primarily used various instruments to observe the geophysical field in Tibet and analyzed the responses of the water temperature and water level to large earthquakes in combination with digital data observed since 2007. Figure 2 and Table 1 show the arrangement of instruments and the distribution of measurement items related to fixed-point deformation, fluids and electromagnetics. The time intervals of sampling are at the order of one minute. Figure 2: (**a**) Distribution of fluid measurement items in Tibet. I, water temperature; II, water level. (**b**) Distribution map of deformation measurement items: I, gravity; II, Vp; III, horizontal pendulum \(\times\) vertical pendulum; IV, volumetric strain; and V, water meter. (**c**) Distribution map of electromagnetic measurement items: I, geomagnetism; II, geoelectricity. In July 2006, we completed the construction of the underground fluid observation well considered herein. The well is approximately 110 m deep, the opening hole diameter is 220 mm, the final hole diameter is 220 mm, the well tube is 165 mm, and the inner diameter is 150 mm. The final well (hole depth) is 111.2 m, and the length of the filter tube is 22.56 m. The length of the ground cable from the observation well to the observation room is approximately 26.5 m. The Lhasa River is approximately 500 m to the south of the observation well. The power supply of the instrument is basically stable. The lithology consists of sands and gravels. The underground fluid instruments installed at the Lhasa geomagnetic station include an LN-3A static water level meter, an SZW-1A water temperature meter, and a WYY-1 comprehensive temperature, pressure, and rainfall meter (SL-3 type tensor) auxiliary observations. The probes of the static water level meter and the surface water temperature meter are set up in the same observation well. The data are collected in the observation room. The temperature probe and the rainfall bucket of the meteorological three-element meter are set up in the station yard. The boundaries around this temperature probe and rainfall bucket are open, and there are no tall buildings nearby. The distance between the temperature probe/rainfall bucket and the observation room is approximately 15 m (Figure 3a). The co-seismic observation of the well covers the major M > 7 earthquakes in the last two decades in the periphery (Figure 3b). The measurements at the Lhasa station include state-of-the-art instruments in China, such as the LN-3A meter (for static water level observation), SZW-1A meter (for water temperature observation), and SL-3 type tensor (for rainfall observation) in the WYY-1 system. The LN-3A digital water level sensor's main technical indicators include a water level range of 0-10 m and an error range for a water level of less than 1 mm, which implies that the measurement accuracy is \(\pm\)0.2% at full scale, and the measurement repeatability is \(\pm\)0.1% at full scale. The overall measurement stability is \(\pm\)0.2% full scale per year, while the dynamic response speed is 1 m/s. The operating temperature ranges from 0 \({}^{\circ}\)C to 40 \({}^{\circ}\)C for the LN-3A water level meter. The analog measurement resolution is a decimal of 4\(\frac{1}{2}\) bits, and the sampling rate (least count) is 1 time per minute for normal events and 1 per second for events. The SZW-1A water temperature meter measurement resolution (error range) is \(<\)0.0001 \({}^{\circ}\)C, with a short-term drift of less than 0.0001 \({}^{\circ}\)C per day and a long-term drift of less than 0.01 \({}^{\circ}\)C per year. The absolute accuracy is \(\pm\)0.05 \({}^{\circ}\)C (given the calibration certificate one by one, 0 \({}^{\circ}\)C-100 \({}^{\circ}\)C range, one calibration point every 5 \({}^{\circ}\)C). The dynamic range is 0-70 \({}^{\circ}\)C. The sampling rate (least count) was once per minute (high-extraction data five times per minute).