This work is devoted to an experimental study of the possible relationship between earthquakes and interplanetary magnetic field (IMF) variations. For the analysis, we use world and regional catalogs of earthquakes and a catalog containing data on the IMF sector structure for several decades. The main methodological technique consists in a comparative analysis of the occurrence rate of earthquakes on the days when Earth crosses the boundary between IMF sectors with the days when Earth is inside the sector. The sign of the IMF radial component is utilized as an indicator of the events on which the oscillation mode of Earth's magnetosphere depends. The sign reversal signals the probable crossing of the boundary between the IMF sectors by Earth, or, in other words, the crossing of the heliospheric current sheet by Earth. The hypothesis about the relationship between IMF variations and seismic activity is that IMF fluctuations, penetrating into the magnetosphere, excite ULF electromagnetic oscillations in the magnetosphere, which, in principle, can affect the physical processes in upcoming earthquake sources. We have found a weak, but statistically significant relationship between IMF variations and seismic activity. We also consider other IMF parameters that control ultra-low-frequency oscillations of the geomagnetic field.