PRESSURE AT DEPTH

TRAVEL TIME CURVES GIVE VELOCITY AT DEPTH TO INTERPRET IN TERMS OF COMPOSITION, WE WANT TO KNOW WHAT MATERIALS COULD EXIST AT THOSE DEPTHS (PRESSURES) AND TEMPERATURES THAT WOULD HAVE THE OBSERVED VELOCITIES

PRESSURE = DENSITY x DEPTH x ACCELERATION OF GRAVITY

SO PRESSURE INCREASES WITH DEPTH

3 km depth => 1000 ATMOSPHERES

400 km => 133,000 ATMOSPHERES

CORE-MANTLE BOUNDARY (2900 km) => 1.3 million ATMOSPHERES

CENTER OF EARTH (6371 km) => 3.5 million ATMOSPHERES

MATERIALS BEHAVE VERY DIFFERENTLY AT THESE CONDITIONS THAN AT SURFACE