Slip and Seismic Radiation Along Bi-material Faults: An Experimental Analysis

Brett M. Carpenter, Ximeng Zu, Xiaowei Chen, & Ze'ev Reches

Submitted August 12, 2016, SCEC Contribution #6630, 2016 SCEC Annual Meeting Poster #027

Large displacements along faults frequently juxtapose crustal blocks of different compositions and mechanical properties. Such juxtapositions have been termed bi-material faults (BFs). It has been theoretically shown that a BF setting may strongly affect rupture characteristics, energy radiation and damage during earthquakes. In order to gain a better understanding of BFs, we designed laboratory experiments on rock samples at conditions similar to earthquake rupture, and present the preliminary results of the mechanical and acoustic characteristics of experimental bi-material faults.

Our experimental faults are composed of contrasting rock pairs of a stiff, igneous block (diorite, granite, gabbro) sheared against a more compliant, sedimentary block (sandstone, limestone, dolomite). The experiments were conducted on a rotary apparatus at velocities up to 0.1 m/s and a normal stress of to 0.5 MPa. The experimental faults were loaded under both constant velocity, relevant to earthquake rupture propagation, and under power-density control. Fault behavior was monitored with stress, velocity and dilation sensors, as well as four 3D accelerometers.

In our preliminary work, we observed differences in mechanical behavior based on the bi-material composition of the fault. We find greater fault parallel deformation and wear in experiments between sedimentary rock types, when compared with those that incorporated igneous rock types. Under power-density loading, we observed differences in the initiation of sliding, stick-slip versus stable sliding, in experiments conducted on a sandstone/gabbro pair and a diorite/diorite pair respectively. These differences were manifested in distinct disparities in the evolution of velocity with slip, which would have important implications for rupture propagation along these faults. We also observed difference in seismic radiation based on the bi-material composition of the fault. In general, we recorded higher amplitude, more impulsive, and more frequent events through igneous rocks, whereas in sedimentary rocks, we recorded lower amplitude, more emergent, and fewer events, as well as tremor like signals. Continuing work is aimed relating our mechanical and acoustic observations to earthquake parameters, e.g., seismic radiation, rise-time, and stress drop, during slip along bi-material faults.

Citation
Carpenter, B. M., Zu, X., Chen, X., & Reches, Z. (2016, 08). Slip and Seismic Radiation Along Bi-material Faults: An Experimental Analysis. Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)