Groundwater Eruption in China Triggered By the 2004 Sumatra Earthquake
Wednesday, 17 December 2014
The 2004 Mw9.3 Sumatra earthquake initiated a large, sustained groundwater eruption in Guangdong, China, 3200 km away from the epicenter. The erupted water column reached a height of ~60 m above the ground surface when it was first sighted and the eruption lasted about 10 days. Estimated seismic energy density at the eruption site is only 0.046 J.m-3; thus it is surprising that the earthquake caused such an intense response. A field survey showed that a large amount of gaseous CO2 was released from groundwater during the eruption and suggested that the eruption was caused by the exsolution of CO2 from groundwater. In this study, we use numerical simulation to explore the mechanism of the well eruption. We apply tidal analysis to water level data from 2003 to 2006 to estimate the aquifer parameters before and after the earthquake; the hydraulic diffusivity inferred this way is 0.423 m2/s and 1.371 m2/s before and after the earthquake, respectively. Based on these parameters, we use TOUGH2, a widely used numerical program for simulating two-phase hydrothermal processes, to simulate the evolution of CO2 saturation, the velocity of erupted groundwater and pressure in the well-aquifer system after Sumatra earthquake. The simulations show that the earthquake may have triggered bubbles to nucleate from the CO2-rich groundwater and enhanced the aquifer permeability, leading to increased groundwater discharge to the well. Decreased pore-pressure in the aquifer caused greater exsolution of CO2 and greater discharge, leading to groundwater eruption. Exsolution of CO2 extends radially away from the wellbore as a function of time and the continued exsolution of CO2 sustained the eruption until pressure in the aquifer drops below hydrostatic, which is marked by a ~9 m drop in groundwater level from that before the earthquake. That earthquake trigger eruption and CO2 exsolution has implications for CO2 sequestration.