BASE GEOPHYSICS

When conducting gravity surveying effects caused by predictable features that are not part of the " geophysical target ." should be removed while the remaining anomaly is then interpreted in terms of sub-surface variations in density. Each known effect is removed from observed data. This is commonly known as gravity data reduction , which I want you to understand its basic concepts. First various " corrections " are described, and then the presentation options are listed. Just keep reading! Methods of gravity data reduction i/ Tidal and Drift corrections When drift and tidal correction is made, then correction is given as  ∆g = g s - g b  Where drift corrected gravity anomaly (∆g) is given as the difference in gravity measured at survey point (gs) and at base station (gb) at the same time. Procedures ➔ Establish the location of one or more gravity base stations ➔ Establish the locations of gravity stations. ➔ Reading relative gravity at the base station and time,...

Induced Polarization (IP) applies the same basic operation and array configuration as resistivity method that If you apply the current into the ground via current electrodes , the voltage can be measured at potential electrodes which are non - polarizable in IP method. The Earth accumulates the charges of applied current at some time, but when the applied current is switched off, the overvoltage will tend to decay slightly (slowly) from its peak value to zero after a certain time interval. This is the capacitive property of the Earth's ground. You can measure the IP effect by using either chargeability or apparent resistivity. Let's see through this post how these two (2) measurements can be deployed to describe IP effect. ip measurement methods What are the two (2) commonly applied methods in IP measurements? Here below are two (2) common IP measurement methods,  i/ Time domain (pulse transient) ii/ Frequency domain 1: time domain ip measurement It measures overvoltage ...

Concept of Gravity Anomaly  Gravity anomaly can be defined as the differences  between the corrected measured gravity and the theoretical (normal) gravity. In most cases gravity anomaly reading is given in milliGal (mGal). As the definition above describes, there are two terms you must understand related to the gravity anomaly such that normal gravity and the observed gravity . Then these terms are described here below in order to get basic insight on this topic. - Normal (theoretical) gravity This is the value of gravity computed without any geological complication. It is computed by the normal gravity formula of the Geodetic reference system. - Observed gravity This is the gravity reading observed at each gravity station after correction have been made for drift and tides. Factors affecting gravity anomaly - Dimensions When we are talking about the dimension of a body we simply mean the size. As the size of the body increases, the probability of producing great gravity att...