Laboratory-observed faulting in intrinsically and apparently weak materials: strength, seismic coupling, dilatancy, and pore fluid pressure

Nicholas M. Beeler

Published 2006, SCEC Contribution #1021

Under some circumstances subduction thrust faulting produces the Earth's largest and most hazardous earthquakes and earthquake induced-tsunamis, but in other localities, large-scale aseismic slip is common and portions of some subduction zones are nearly completely aseismic. Understanding the particular conditions that lead to seismic rather than fault slip is critical for improving earthquake and tsunami hazard estimates in subduction zones and is a major objective of the NSF-MARGINS initiative. This paper reviews laboratory rock mechanics observations of rock fracture and fault slip relevant to seismic shallow crustal faulting, emphasizing differences between behavior of intrinsically weak and strong faults and identifying the underlying physical processes and conditions that influence fault strength. These lab rock friction and rock failure observations, made primarily on strong faults and intact rock, largely suggest that earthquake occurrence is a result of dilatancy. As many subduction zones appear to be profoundly weak, the conditions for seismicity are considered in the context of intrinsic fault weakness, and under circumstances of apparent weakness due to high pore pressure. The principal conclusion of this review is that in the absence of chemical effects of fluids on fault strength, both intrinsic weakness and apparent weakness resulting from high pore pressure tend to encourage aseismic over seismic slip.

Citation
Beeler, N. M. (2006). Laboratory-observed faulting in intrinsically and apparently weak materials: strength, seismic coupling, dilatancy, and pore fluid pressure. , : Columbia University press.