Pioneering Seismology Establishes New World Record in Deep Sea Drilling

japan_quake_map_bbcHeat in subduction zone slip-faults is indicative of stress, rupture propagation, and the vertical ground displacement of an earthquake at that fault. In the 2011 magnitude 9.0 Japan earthquake, this vertical displacement generated a 40 meter-high tsunami, killing thousands, cutting off electricity and water to millions, and costing overall $235 billion, making this event the most expensive natural disaster in history.  JAMSTEC (Japan Agency for Marine Science and Technology), along with the Integrated Ocean Drilling Program (IODP) immediately started JFAST (Japan Trench Fast Drilling Project), to inquire the earthquake’s geophysical mechanisms and the predictability of future tsunamis and megaquakes. This international collaboration has not only produced profound insight on slip ruptures by studying the frictional heat signature along the Nankai Subduction Zone in the Japan Trench, East Japan, but is also the first scientific endeavor to pursue the energy dynamics of an earthquake at a plate boundary subduction fault directly following an earthquake.

japan_quake_map1After determining the area’s important geological properties by core sampling at shallower depths, the state-of-the-art Scientific Drilling Vessel Chikyu, set out in April of 2012 to conduct the initial drilling and piping of the wellhead.  This required lowering a 7-kilometer long pipe of about 15 centimeter diameter from the ship to the bottom of the Japanese trench and securing a wellhead at a total water depth of 6,889.5 m plus 30 m drilled.  This is just below the previous Challenger Deep world record of 7,034 m water depth plus 15.5 m drilled.  Returning to the site in July, the expedition team drilled further to 850.5 m subsurface and lowered a temperature observatory, consisting of an array of 55 detachable high-precision temperature sensing loggers in a tube, directly through the plate boundary fault line to a total depth of 855 m, bringing the expedition’s paramount depth to 7,752.31 m below the sea surface.  “The temperature sensors have to be detachable in case there is significant further slip of the plates, as can occur after a megaquake,” explained Dr. Patrick Fulton, a scientist in the JFAST expedition at the UC Berkeley Earth and Planetary Science kick-off department seminar.

The temperature observatory measures residual energy in a way that allows scientists to spatially correlate dissipated heat with rupture mechanics and understand why the earthquake could cause such a powerful tsunami.   In April of 2013, one year after initial drilling, the team recovered all of the temperature sensors and used them to determine the frictional heating generated at the fault during the 2011 Japan quake.

Earlier this year Fulton and his colleagues published evidence indicating that a complete drop in stress at the fault caused the drastic slip and vertical displacement that made the 2011 Japan earthquake so destructive. Their work is extremely enlightening to the seismology community and to human understanding of these kinds of phenomenon.  Future discoveries as a result of this major undertaking are highly anticipated. This kind of scientific understanding is a stepping stone to a future goal of predicting earthquakes and developing tsunami warning systems in areas of high vulnerability. Warning systems such as this may prevent the dangerous meltdowns experienced by coastal nuclear power plants, such as Japan’s nuclear catastrophe following the 2011 tsunami.