Seismic Slip‐Pulse Experiments Simulate Induced Earthquake Rupture in the Groningen Gas Field

• Published in: Geophysical research letters Vol. 48; no. 11; pp. e2021GL092417 - n/a
• Main Authors: Hunfeld, Luuk B., Chen, Jianye, Niemeijer, André R., Ma, Shengli, Spiers, Christopher J.
• Format: Journal Article
• Language: English
• Published: United States John Wiley and Sons Inc 16.06.2021
• Subjects: dynamic weakening; fault gouge friction; Fractures and Faults; Groningen gas field; high‐velocity slip‐pulse experiments; induced seismicity; Research Letter; Rheology and Friction of Fault Zones; Role of Fluids; Structural Geology; Tectonophysics; thermal pressurization; thermal pressurization; high‐velocity slip‐pulse experiments; induced seismicity; Groningen gas field; dynamic weakening; fault gouge friction
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL092417

Rock materials show dramatic dynamic weakening in large‐displacement (m), high‐velocity (∼1 m/s) friction experiments, providing a mechanism for the generation of large, natural earthquakes. However, whether such weakening occurs during induced M3‐4 earthquakes (dm displacements) is unknown. We performed rotary‐shear experiments on simulated fault gouges prepared from the source‐, reservoir‐ and caprock formations present in the seismogenic Groningen gas field (Netherlands). Water‐saturated gouges were subjected to a slip pulse reaching a peak circumferential velocity of 1.2–1.7 m/s and total displacements of 13–20 cm, at 2.5–20 MPa normal stress. The results show 22%–81% dynamic weakening within 5–12 cm of slip, depending on normal stress and gouge composition. At 20 MPa normal stress, dynamic weakening from peak friction coefficients of 0.4–0.9 to 0.19–0.27 was observed, probably through thermal pressurization. We infer that similar effects play a key role during induced seismic slip on faults in the Groningen and other reservoir systems. Plain Language Summary During large, natural earthquakes, rapid sliding motion on faults through several meters of displacement generates large amounts of frictional heat. This triggers mechanisms that cause crushed fault rocks to weaken drastically, allowing the rupture to propagate, and the earthquake to grow. However, whether this occurs during relatively small, human‐induced seismicity, caused by hydrocarbon production or fluid injection in the subsurface, for example, is unknown. Here we simulate seismic fault slip during magnitude 3 to 4 earthquakes, using crushed rock materials derived from the seismogenic Groningen gas field (Netherlands). Our experiments show that even for short‐displacement (dm), representative for such induced earthquakes, the fault rocks weaken significantly (22%–81%), depending on mineralogy and on the normal stress acting on the fault. These findings provide insights for the larger induced events recorded in Groningen (magnitude up to 3.6), and improve hazard assessment capabilities using numerical models. Key Points We report dm‐displacement, high‐velocity slip‐pulse experiments on fault gouges prepared from key Groningen gas field lithologies All gouges show dynamic weakening with strength drops in the range 22%–81%, depending on normal stress and gouge composition Dynamic weakening was likely caused by thermal pressurization yielding minimum friction coefficients of 0.19–0.27 at 20 MPa normal stress