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| | Abstract | | Magnetotelluric (MT) response functions are well known to be affected by the spatial or strength property of source field. However, there are several cases that the temporal changes of MT responses over the estimated errors cannot be explained simply by the source field. Therefore, we evaluated the cause of such cases taking the spatial and strength property of geomagnetic variations into consideration. We derived SSQ impedance (rotational invariants) from the MT data acquired at Kakioka Magnetic Observatory, Japan. Moreover, we derived the spatial and strength property of geomagnetic variations in order to evaluate the effect of source field on the SSQ impedance. As a result, the SSQ impedance changed temporally over their estimated errors even under the condition that the spatial and strength property of geomagnetic variations did not vary. Also, there are clear difference of precipitation amount between before and after such SSQ impedance's changes. The SSQ impedance's changes may possibly reflect the subsurface environment although we cannot know the condition of source field perfectly. |
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