Analysis of fault rupture processes by earthquake-like slipevents in the laboratory

University Of Oklahoma Norman Campus, Norman OK

Investigators

Abstract

The investigators propose to analyze experimentally the processes of initiation, acceleration and self-healing of seismic slip at a patch on the surface of a fault. The experiments will be conducted on a new rotary shear apparatus that allows testing frictional sliding along rock blocks for large slip (a few meters), slip-velocity of ~1 m/s, and normal stress up to 30 MPa. Further, the design of this apparatus allows application of a finite amount of stored energy on a fault surface (up to 107 J/m2) for a short period of time (up to 5 s). Their preliminary results show that these conditions can generate an Earthquake-Like lip Event (ELSE) along the rock sample with rise time <0.1 s, slip velocity up to 1 m/s, slip-distance up to 3 m, and self-healing (strength recovery and rupture arrest). They propose to use the unique capabilities of this apparatus for an extensive series of ELSE experiments that are analogous to earthquake processes at a fault patch under in-situ loading conditions. These experiments will allow analyzing fundamental earthquake parameters, such as rise-time, weakening, self-healing, slip velocity, slip distance, heat generation and energy dissipation under laboratory-controlled conditions. The objectives of the project is to improve the apparatus capabilities in two main aspects: 1. Stiffening of the loading frame to eliminate (or significantly reduce) the unstable shattering at high velocities. 2. Develop and implement the torque control system that will allow us to simulate a wide range of earthquake scenarios. A typical earthquake starts at a small nucleus and propagates as a fast moving rupture front along a fault surface. Every patch on the fault surface is at rest before the earthquake, it is accelerated to slip velocity of about 1 m/s by the rupture front and it stops slipping when the elastic energy that was stored prior to the earthquake has been dissipated. Thus, the patch experiences abrupt acceleration and deceleration over periods from a fraction of a second to a few seconds. During this period of intense acceleration/deceleration, the patch friction changes dramatically without steady-state velocity. On the other hand, typical experimental studies of fault friction are designed to determine the steady-state friction that probably does not realized during earthquakes. The proposed research eliminates this fundamental experimental limitation by utilizing the unique capabilities of an apparatus that was built recently in University of Oklahoma. The apparatus is suitable to simulate earthquake-like events as it can load a laboratory rock patch by energy stored in a massive flywheel (225 kg). This unique, advanced design of the our experimental system allows simulating earthquake rupture processes under in-situ conditions of (1) high stress and high velocity; (2) finite energy supply; and (3) stress and velocity control. The proposed experiments will provide better links between experiments, theory and seismic concepts, and, by doing so, will significantly advance the understanding of earthquake rupture processes, earthquake energy balance, physics of fault weakening, and the scaling of slip rates, slip magnitude, and radiated energy.