Laboratory‐developed contact models controlling instability on frictional faults

Abstract

Laboratory experiments were performed on a polymethyl methacrylate (PMMA)-PMMA frictional interface in a direct shear apparatus in order to gain understanding of fault dynamics leading to gross rupture. Actual asperity sizes and locations along the interface were characterized using a pressure-sensitive film. Slow aseismic slip accumulated nonuniformly along the fault and showed dependency on the applied normal force-increased normal force resulted in higher slip gradients. The slow slip front propagated from the trailing (pushed) edge into a region of more densely distributed asperities at rates between 1 and 9.5 mm/s. Foreshocks were detected and displayed impulsive signals with source radii ranging between 0.21 and 1.09 mm; measurements made using the pressure-sensitive film were between 0.05 and 1.2 mm. The spatiotemporal clustering of foreshocks and their relation to the elastodynamic energy released was dependent on the normal force. In the region where foreshocks occurred, qualitative optical measurements of the asperities along the interface were used to visualize dynamic changes occurring during the slow slip phase. To better understand the nucleation process, a quasi-static asperity finite element (FE) model was developed and focused in the region where foreshocks clustered. The FE model consisted of 172 asperities, located and sized based on pressure-sensitive film measurements. The numerical model provides a plausible explanation as to why foreshocks cluster in space and observed a normal force dependency and lend credence to Ohnaka's nucleation model.

Analysis of Microseismicity Framing ML > 2.5 Earthquakes at The Geysers Geothermal Field, California

“…This is in contrast to the more recent work of Bouchon et al () and Brodsky and Lay () who suggest that foreshocks are more common. This is in agreement with many laboratory studies showing foreshock activity prior to stick slip events (Goebel et al, ; Lei et al, ; Selvadurai & Glaser, ). Zaliapin and Ben‐Zion () identified seismicity clusters using nearest‐neighbor distributions in a space‐time and magnitude domain and found that an increased occurrence of foreshocks occurs in areas displaying high heat flow.…”

Slow and fast ruptures on a laboratory fault controlled by loading characteristics

“…When we opened the fault and inspected the surface, we observed an increased amount of striations and gouge within ~25 mm of the sample ends, indicating higher wear rates there. Other work on direct shear machines has shown a similar nonuniform distribution in normal stress [ Ben‐David et al ., ] and in density of asperity contacts [ Fukuyama et al ., ; Selvadurai and Glaser , ].…”

Temporal variation of tectonic tremor activity in southern Taiwan around the 2010 ML6.4 Jiashian earthquake

“…Many studies based on observations [ Bouchon et al ., ; Kato and Nakagawa , ], laboratory experiments [ Selvadurai and Glaser , ], and modeling [ Avouac , ] have suggested slow aseismic slip during the prenucleation process of a fast‐ rupturing earthquake. Such an aseismic process could increase stress in surrounding areas and trigger foreshocks [ Ohnaka , ; Bouchon et al ., ; Ito et al ., ; Kato and Nakagawa , ].…”