How strong is an asperity?

Journal Article · Fri Jan 02 04:00:00 EST 1998 · Journal of Geophysical Research-Solid Earth

OSTI ID:834407

Sammis, Charles G ^[1]; Nadeau, Robert M; Johnson, Lane R

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1. LBNL Library

A recent study of repeating earthquakes on the San Andreas Fault in central California by Nadeau and Johnson [1998] found that the smallest events occurred on patches having a linear dimension of the order of 0.5 m, displacements of about 2 cm, and stress drops of the order of 2000 MPa, roughly 10 times larger than rock strengths measured in the laboratory. The stress drop for larger events was observed to decrease as a power law of the seismic moment reaching the commonly observed value of 10 MPa at about magnitude 6. These large strengths are shown here to be consistent with laboratory data if the preexisting microcracks are all healed. A hierarchical fractal asperity model is presented, which is based on recent laboratory observations of contact distributions in sliding friction experiments. This ''Cantor dust'' model is shown to be consistent with the observed power law decrease in stress drop and increase in displacement with increasing event size. The spatial distribution of hypocenters in the Parkfield area is shown to be consistent with this simple fractal model and with a hierarchical clustering of asperities having a fractal dimension of D=1 and discrete rescaling factor of about 20.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Office of Basic Energy Sciences, Lawrence Livermore National Laboratory. Institute of Geophysics and Planetary Physics Grant; U.S. Geological Survey. National Earthquake Hazards Reduction Program Award 1434-95-G2540, Defense Special Weapons Agency Grants DSWA-01-97-1-0026 and DSWA-01-97-1-0005, National Science Foundation Grant EAR-9508040 (US)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 834407
• Report Number(s): LBNL--44998
• Journal Information: Journal of Geophysical Research-Solid Earth, Journal Name: Journal of Geophysical Research-Solid Earth Journal Issue: B5 Vol. 104
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
DIMENSIONS
EARTHQUAKES
FRACTALS
HYPOCENTERS
SLIDING FRICTION
SPATIAL DISTRIBUTION