HR: 1330h
AN: T22B-0507    [PDF]
TI: Evolution of Fault Systems and its Associated Geomorphic Structures: Strike-Slip and Dip-Slip Fault Model Test and Field Survey
AU: * Ueta, K
EM: ueta@criepi.denken.or.jp
AF: Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba, 270-1194 Japan
AB: Sandbox experiments were performed to investigate evolution of fault systems and its associated geomorphic structures caused by strike-slip and dip-slip motion on basement faults. A 600 cm long, 250 cm wide, and 60 cm high sandbox and a 200 cm long, 40 cm wide, 25 cm high sandbox were used in a strike-slip fault model test. Computerized X-ray tomography applied to the sandbox experiments made it possible to analyze the kinematic evolution, as well as the three-dimensional geometry, of the faults. The deformation of the sandpack surface was analyzed by use of a laser method 3D scanner, which is a three-dimensional noncontact surface profiling instrument. In the dip-slip fault test, a 332.5 cm long, 200 cm high, and 40 cm wide sandbox was used. The fault type, fault dip, fault displacement, thickness and density of sandpack and grain size of the sand were varied for different experiments. Field survey of active faults in Japan and California were also made to investigate the evolution of fault systems and its associated geomorphic structures. A comparison of the experimental results with natural cases of active faults reveals the following: (1) In the left-lateral strike-slip fault experiments, the deformation of the sandpack with increasing basement displacement is observed as follows. a) In three dimensions, the right-stepping shears that have a "cirque" / "shell" / "ship body" shape develop on both sides of the basement fault. The shears on one side of the basement fault join those on the other side, resulting in helicoidal shaped shear surfaces. Shears reach the surface of the sand near or above the basement fault and en echelon Riedel shears are observed at the surface of the sand. The region between two Riedels is always an up-squeezed block. b) Lower-angle shears generally branch off from the first Riedel shears. c) Pressure ridges develop within the zone defined by the right-stepping helicoidal shaped lower-angle shears. d) Grabens develop between the pressure ridges. e) Y-shears offset the pressure ridges. f) With displacement concentrated on the central throughgoing fault zone, a liner trough developed directly above the basement fault. R1 shears and P foliation are observed in the liner trough. Such evolution of the shears and its associated structures in the fault model tests agrees well with that of strike-slip fault systems and its associated geomorphic structures. (2) Low-angle and high-angle reverse faults commonly migrate basinward and rangeward with time, respectively. With increasing normal fault displacement in basement, normal fault develops within range after reverse fault has formed along range front. (3) In the fault model tests, the horizontal distance of surface rupture from the basement fault normalized by the height of sandpack (W/H) does not depend on the height of sandpack and grain size of sand. The values of W/H from the fault tests agree well with those of earthquake faults in alluvium.
DE: 7819 Experimental and mathematical techniques
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8107 Continental neotectonics
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting