In order to investigate changes in the geomagnetic field associated with seismic activity in the western part of the North Anatolian Fault Zone (NAFZ), seven continuous measurement stations and eighteen repeated-survey sites were set up in the Inik-Geyve region, taking into account the fault trace and its features. Simple differences in the total intensity between these continuous stations have been derived for detecting possible anomalous phenomena associated with earthquake occurrences. Theoretical studies imply that changes in the total intensity associated with fault activity are larger in the case of non-uniform distribution of rock magnetization than those in the uniform case. Meanwhile, inversion analyses of magnetic anomalies at the North Anatolian Fault Zone (NAFZ) suggest a dyke-like structure extending parallel to the fault strike. This structure enables us to test our strategy, based on non-uniform magnetization, for detecting pre- and/or co-seismic changes in the geomagnetic field. We made a theoretical estimation of geomagnetic changes for the case of a magnetic dyke structure intruding a non-magnetic body parallel to the strike of a fault. It turns out that, unlike the uniform case, the magnetic field arising from stress-induced magnetization is enhanced. A tectonomagnetic observation system taking into account such a non-uniform magnetization structure in the Inik-Geyve region of the NAFZ is also described.