Three dimensional propagation directions of electromagnetic pulses detected in the earth

Completing a tri-axial electromagnetic (EM) sensor system used in a narrow borehole, and inserting it into 150 m deep borehole constructed on a seashore, we began to measure three dimensional arrival directions of EM pulses detected in the earth by means of strict calculation of Poynting vector. Measured arrival directions have shown clear difference in EM environment between on the landside and seaside of the observation point on the seashore. On the landside, many up-propagating lightning EM pulses were detected, which would result from their reflections at deeper layers than the sensor depth after penetrating into the ground. Another is less detections of EM pulses on the seaside, which is due to strong decay of lightning EM pulses penetrated into the sea water. The less detections of lightning EM pulses on the seaside suggests favorable situation for the observation of earth-origin EM pulses.