CSIR NET June 2016 Q91: Geophysics
Upward continuation of a potential-field (gravity) anomaly progressively smooths and attenuates sharp, near-surface anomalies, reducing amplitude contrasts across abrupt density boundaries like faults.
Point A sits over the low (down-thrown/lower-density) side, C over the high (up-thrown/higher-density) side, and B lies near the transition (fault trace) where the anomaly is already close to the regional average. Upward continuation smooths the sharp step: the low value at A rises toward the average (g'_A > g_A), the high value at C falls toward the average (g'_C < g_C), while B, already near the average/inflection point, remains essentially unchanged (g'_B = g_B). Option 4 is correct.
1), 2), 3) Incorrect — these assume both A and C anomalies weaken toward the average in the same direction consistent with smoothing, but get the direction wrong at A (predicting a decrease rather than increase) or misstate the C/B relationship. 4) Correct — matches the expected smoothing behavior of upward continuation across a fault-bounded density step: rise at the low point, fall at the high point, no change at the near-average midpoint.