Earthquakes begin when a fault ruptures at a single point, and the rupture continues to spread out until something causes it to stop. In other words, the size of an earthquake depends in part on the size and shape of the fault it causes to move. In this research, our team mapped small faults that used to be active about 90 millions of years ago. At the time, they were buried deep below the surface. Over time, uplift and erosion have peeled away the overlying layers of rock, revealing the ancient fault zone. Today, you can walk along the fault from end to end in the beautifully exposed granite slopes of the Sierra Nevada mountains. We documented how the shape of a fault’s end could have caused it to stop growing bigger. The process could be similar to the processes that stop earthquakes from growing bigger.
Monday, April 26, 2010
What happens at the end of fault zones?
Publications:
d'Alessio, M. A. and S. J. Martel, 2004. Fault terminations and barriers to fault growth. Journal of Structural Geology 26 (10), 1885-1896.
This picture comes from a highway on the Big Island of Hawaii. While the sign makes it sound like the fault zone termination is simple and easy to spot, our research shows that the ends of faults can be much more complicated.
Joints in granitic rock make weaknesses that faults can exploit. These joints stopped the growth of a fault in the John Muir Wilderness of the Sierra Nevada mountains.