A longstanding scientific puzzle has recently been solved by a geological research team when they discovered evidence that some minor earthquakes are initiated by groundwater pressure.
The research team, led by Ma Kuo-fong (馬國鳳), a professor in National Central University’s department of Earth sciences, and researchers from the US and Japan, and funded by the National Science Council, yesterday announced their discovery of the world’s first direct and precise evidence of the causal relationship between the water pressure of flowing groundwater and some minor earthquakes.
“Scientists have always tried to figure out how earthquakes are caused and several hypotheses of earthquakes initiated by water pressure have been brought up in research, but there were no actual observed evidence to prove the hypotheses,” Ma said at the council’s headquarters in Taipei yesterday.
Most earthquakes are caused by fault movements and the shear force of the movement in differing directions along both sides of a fault, but the team discovered that minor earthquakes of about magnitude 0 to magnitude 1.5 could be caused by increased groundwater pressure below the slip band at a fault and has nothing to do with seismic shear force.
During the Taiwan Chelungpu-fault Drilling Project that began in 2006, the team drilled a 1,300m deep borehole into the Chelungpu fault in central Taiwan — the fault that caused the devastating 921 Earthquake in 1999 — and placed seven seismometers to collect seismic data between 950m and 1,300m deep into the fault.
The team observed that when the flow of groundwater gets blocked by the impermeable zone of the slip band, the water pressure increases, and when the pressure exceeds the crustal stress, it releases an explosive force outwards. This “explosion” causes a minor earthquake.
The minor earthquakes caused by water pressure were named “isotropic events” by the team, due to them being caused by an explosive force of water, she said.
The discovery was published in Science magazine last month.