The Lands Geological Survey Division of the MGB Central Office conducted a virtual training on IRIS

Syscal Pro Switch-72 Resistivity Meter on 2021. October 11-13. The objective of the training was to teach MGB geologists on how to use and handle the IRIS Syscal Pro Switch-72 Resistivity Meter. The training was held virtually via the GoToMeeting Online Platform (gotomeet.me). Lectures on the theories, concepts, and methodologies of various resistivity surveys were provided by Bing Bong S. Salinas, Senior Geologist of the De Leon Import and Export Corporation. The lecturer also presented how the data is interpreted using WinSev and Res2dinvx64 software.

A resistivity meter is an electrical equipment utilized in the conduct of earth resistivity surveys – a type of geophysical method for determining subsurface geological features. Resistivity surveys employ electrical currents which are introduced into the ground through metal probes (current probes). As the current passes through the ground, the varying · degrees of resistivity of subsurface features weakens the said current. The lingering voltage is detected by another set of metal probes (potential probes) and the resistivity meter measures this to determine the local resistivity in the area.

Various configurations of the metal probes can be used depending on the study being done. For MGB’s groundwater assessment project, the Schlumberger array is employed. The Schlumberger array is a configuration where the metal probes are arranged linearly, with two current probes positioned near to the resistivity meter (one on each side), and two potential probes placed farther (also one on each side of the resistivity meter). The probes are spaced evenly on both sides of the resistivity meter following a specified distance of placement from the device. As the survey proceeds, the probes are continually spread out after each reading: the farther the spread of the probes, the deeper the penetration of the electrical current, and thus resulting to a deeper determination of subsurface features.

The data is then tallied and uploaded into a computer where a certa’in software is able to read the data. High resistivity values indicate a low water content and vice versa. The varying resistivity along a profile denotes different rocks and geologic features (e.g. mudstones usually manifest higher resistivity values compared to sandstones).