Fig 1.
(1) Distribution of karst systems in the study area; (2) Temperature distribution in Geothermal Anomaly Zone 1; (3) Temperature distribution in Geothermal Anomaly Zone 2.
Fig 2.
Temperature Variation with Depth in Investigation Boreholes CK1, CK2, and CK3.
Table 1.
Temperature Correction for Diurnal Variation.
Table 2.
Surface feature-based temperature calibration.
Table 3.
Corrected results of shallow layer temperature measurement.
Table 4.
Modeling parameters determined from laboratory measurements and field test data.
Table 5.
Flow velocity versus equivalent diameter.
Fig 3.
Geometric model and boundary condition setup for karst structures: (1) geometric model; (2) top boundary temperature condition; (3) temperature distribution across the pipe wall [34].
Fig 4.
Thermal Profiles and Differences Between Karst and Non-Karst Structures.
(a) Comparison of temperature profiles between a karst structure at 50 m depth and and non-karst formation; (b) temperature difference curve between karstic and non-karstic bodies at 2 m depth.
Fig 5.
Inferring Karst Conduit Scale from Shallow Thermal Signals.
(a) Relationship between the maximum depth and equivalent diameter of the 13.45°C isotherm; (b) Variation of subsurface temperature at 2 m depth with karst equivalent diameter.
Fig 6.
Temperature at 2 m depth as a function of equivalent karst diameter for a flow velocity of 0.269 m/s.
Fig 7.
Temperature difference curve at 2m depth: karst vs. non-karst under various fluid temperatures.
Table 6.
Estimated initial parameter values of karst structures for each survey line.
Fig 8.
Spatial distribution of estimated geothermal temperature along various survey lines in Low-Temperature Anomaly Zone 1 derived by parameter estimation.
Fig 9.
The spatial distribution of geothermal isotherms derived from parameter estimation across all survey lines in Low-Temperature Anomaly Zone 2.
Fig 10.
Temperature Profile Fitting and Inferred Karst Conduits in Anomaly Zone 1.
(a) the fitting results of four 2m-depth temperature profiles in Low-Temperature Anomaly Zone 1; (b) potential karst channel locations inferred based on temperature profiles.
Fig 11.
Temperature Profile Fitting and Inferred Karst Conduits in Anomaly Zone 2.
(a) The fitting results of three 2m-depth temperature profiles in Low-Temperature Anomaly Zone 2; (b) potential karst channel locations inferred based on temperature profiles.
Table 7.
Burial depth and flow radius of karst structures from different survey lines.