Abstract
It is important to distinguish between natural earthquakes and those induced by CO2 injection at carbon capture and storage sites. For example, the 2004 Mw 6.8 Chuetsu earthquake occurred close to the Nagaoka CO2 storage site during gas injection, but we could not quantify whether the earthquake was due to CO2 injection or not. Here, changes in pore pressure during CO2 injection at the Nagaoka site were simulated and compared with estimated natural seasonal fluctuations in pore pressure due to rainfall and snowmelt, as well as estimated pore pressure increases related to remote earthquakes. Changes in pore pressure due to CO2 injection were clearly distinguished from those due to rainfall and snowmelt. The simulated local increase in pore pressure at the seismogenic fault area was much less than the seasonal fluctuations related to precipitation and increases caused by remote earthquakes, and the lateral extent of pore pressure increase was insufficient to influence seismogenic faults. We also demonstrated that pore pressure changes due to distant earthquakes are capable of triggering slip on seismogenic faults. The approach we developed could be used to distinguish natural from injection-induced earthquakes and will be useful for that purpose at other CO2 sequestration sites.
Highlights
Subduction zones along active convergent plate margins are areas of high seismicity that drive mountain building processes [1,2]
As a result of fluid flow simulation considering the geological condition in this study area, the pore pressure and CO2 saturation distribution results can be consistent with the history of CO2 injection at the Nagaoka site in Figure 2 [29,30,40]
The changes in pore pressure caused by injection of CO2 at the Nagaoka CO2 storage site were examined and compared to natural variation
Summary
Subduction zones along active convergent plate margins are areas of high seismicity that drive mountain building processes [1,2]. Snowfall and rainfall can increase subsurface pore pressure either by hydraulic loading of shallow sediments or by deeper pressure diffusion within fault zones [15,18,19,20,21] Human activities such as groundwater extraction and fluid injection (e.g., CO2 storage) can change the subsurface stress regime and trigger earthquakes [18,20,22,23]. Because the distances of both of these facilities were not far from the earthquake epicenters, people worried about the relationship between the earthquakes and CCS activities Apart from this issue, the location of the Japanese Islands on an active subduction zone means that a reliable method is needed to distinguish between natural subduction-related earthquakes and those possibly induced by CO2 injection. Application of the approach presented here will contribute to distinguishing natural earthquakes from those induced by CO2 injection during CCS projects
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