At first glance, air hockey – a fast-paced arcade game – and induced seismicity – earthquakes triggered by human activity – seem unrelated. Yet, both share a fascinating connection through the physics of reduced friction. The key lies in how airflow under an air hockey puck mirrors the increase in pore pressure along fault planes, facilitating an easier ability to move in unexpected ways.
In air hockey, the table’s surface is perforated with tiny holes that release a thin cushion of air, lifting the puck and reducing friction. This allows the puck to glide effortlessly, enabling quick, smooth plays. The airflow effectively counteracts the table’s resistance, much like how increased pore pressure – fluid forced into rock pores – can potentially destabilise faults in the Earth’s crust.
In induced seismicity, activities like hydraulic fracturing or wastewater injection can potentially elevate pore pressure along pre-existing fault planes, lowering the effective normal stress that may otherwise keep dormant faults locked.
Although pore pressure plays a critical role in induced seismicity, fault orientation relative to the regional stress field and the coefficient of friction are also crucial. Faults critically oriented to the regional stress field are more prone to slip when subject to an increase in pore pressure from fluid injection, which reduces the effective normal stress clamping the fault.
The coefficient of friction, which governs fault stability, determines how easily a fault slips under these conditions. When pore pressure sufficiently lowers the frictional resistance on a critically stressed fault, it can trigger seismic events, ranging from microearthquakes to larger tremors, depending on the fault’s characteristics and stress state.
This analogy simplifies induced seismicity for non-experts, dispelling exaggerated notions of “man-made” earthquakes. It clarifies that the process involves more than just “lubricating” fault planes, as often assumed with saltwater disposal (SWD). The analogy provides practical insights for the energy sector. Like air hockey players adjusting tactics to control puck momentum, geoscientists can reduce seismic risks by optimizing injection rates and selecting low-risk zones, preferably away from faults.
