PROBING THE DEEP EARTH

CORE SHADOW ZONE

THE LIQUID IRON OUTER CORE HAS LOWER P-WAVE SPEED THAN THE ROCKY MANTLE, SO P-WAVES ENTERING IT (called PKP) ARE BENT DOWNWARD

NO S-WAVES CAN PROPAGATE THROUGH IT

THUS THERE IS A SHADOW ZONE WHERE P ARRIVALS ARE WEAK AND DIRECT S WAVES DO NOT ARRIVE

(USGS)

THESE TRAVEL TIME CURVES SHOW THE CORE'S DEPTH AND

VELOCITY, WHICH IS WHAT WE EXPECT FOR IRON UNDER THESE CONDITIONS