THIS WEEK
FRIDAY APRIL 21 @ 1P PDT
Capturing co-seismic fault deformation and pseudotachylyte formation to unveil earthquake physics
Nicola Tisato, University of Texas at Austin
Earthquake mechanics is still far from being completely understood, and recent observations have challenged our models. For example, we do not yet understand what controls the occurrence of slow-slip events vs. destructive seismic events. Therefore, new methods to investigate earthquake mechanics are essential to close such a gap. Here, I will discuss results obtained from an Energy-Controlled-Rotary (ECoR) shear apparatus that can produce spontaneous high-intensity slip events. Pairing ECoR with high-speed imaging allowed for capturing precursors and slow-slip events during interseismic periods and the co-seismic evolution of melt within the fault. ECoR challenges the paradigm of performing rotary shear experiments by imposing velocity and displacement and allows the weakening and strengthening processes to control the slip. The experiments show that melt during the seismic slip undergoes specific phases – promoting or impeding slip – that such phases can be clearly identified in acoustic emission signals akin to seismic waves during earthquakes. [more info] [register]
Coming in May
FRIDAY MAY 5 @ 1P PDT
The role of fault asperity in the generation of laboratory earthquake
Lifeng Wang, State Key Laboratory of Earthquake Dynamics, China Earthquake Administration
Fault asperity is often deemed to be responsible for occurrences of seismic clusters, repeating earthquakes, or concentrated slip during large events. However, because of the inaccessible fault surface, its possible presence and relevant role in mechanical controls are still based on indirect inferences from fault activities, and a direct measure of the roles of fault asperity is still missing. Here, we take the advantage of a rock experiment about two half-meter granite plates with apparent asperity structures. Acoustic emission and fault slip measurements, assisted by numerical simulation, unveil asperity acting as a mechanical attractor to small events during the interseismic phase, while as a barrier to slow slip during the mainshock nucleation. The slip deficit long hosted by asperity is finally filled up, producing the largest coseismic slip there. The full scenario unfolds how fault asperity partitions stress in both temporal and spatial domains, constituting a physical link about the background seismicity, foreshocks, preseismic slow slip and the characteristic mainshock. [more info] [register]