Deep earthquakes triggered by the olivine-poirierite transition‎

Seismicity decreases with depth because elevated confining pressure prevents frictional sliding of faults. However, seismicity tends to increase with depth in the mantle transition zone (depths of 410−600km). It has been believed that pressure-induced phase transitions of olivine in the "cold" subducted slabs is the cause of high seismicity in the mantle transition zone.