The effect of fluid pressurization on energy partitioning during the earthquake cycle

maryam alghannam, hector gomez, & ruben juanes

Published September 11, 2022, SCEC Contribution #11992, 2022 SCEC Annual Meeting Poster #133

During an earthquake, the potential energy stored in the Earth is released as frictional
energy, fracture energy, and radiated energy in the form of seismic waves. The potential
energy released is mainly comprised of elastic strain energy and gravitational energy. While
several studies have considered estimating the radiated energy and energy partitioning, exist-
ing descriptions have not addressed the contribution of fluid pressurization to the potential
and seismic energy budget—a key aspect toward understanding the physical mechanisms
behind the link between fluid injection and induced earthquakes.
Here, we model potential and radiated energy during an induced earthquake cycle by
calculating dynamic fault slip using a single-degree-of-freedom spring poroslider and rate-
and-state friction [1]. The spring-poroslider represents a fault segment in contact with a
reservoir. The simulation model is based on the balance of internal energy of the spring,
frictional and fracture energy, and the energy dissipated by viscous forces in the fluid. Using
an analysis of a multi-degree-of-freedom system, we show that seismic radiation can be
modeled within the single-degree-of-freedom spring slider by adding a viscous damping term.
We then use the model to study fluid pressurization and assess its contribution to the
potential and seismic energy budget.
We find that: (1) late injection needs lower amount of fluid to trigger earthquakes com-
pared to the amount needed to induce earthquakes early in the cycle, (2) there is a week
dependency of the radiated energy and seismic efficiency on the timing of fluid injection
within the earthquake cycle for low injection rate compared to high injection rate, (3) the
rate of fluid pressurization is correlated to stress drop, total slip, radiated energy, and seismic
efficiency through the influence of the rate of fluid pressurization on the dynamic coefficient
of friction, and (4) fluid injection leads to bigger earthquakes overall.

References
[1] M Alghannam and R Juanes. Understanding rate effects in injection-induced earthquakes. Nature
Communications, 11(1):1–6, 2020.

Citation
alghannam, m., gomez, h., & juanes, r. (2022, 09). The effect of fluid pressurization on energy partitioning during the earthquake cycle. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)