Is California's Big One coming?
In 1992 and in 2004, remote earthquakes caused changes to the San Andreas fault; in both cases, there were distinct changes in the movement of fluids and an increase in the frequency of micro-earthquakes deep within the fault below Parkfield; what will be the effect on the fault of the recent Sumatra earthquake?
Call it a geological butterfly effect. Fenglin Niu of Rice University in Houston, Texas, and colleagues believe they have found two clear cases where remote events weakened the San Andreas fault near Parkfield, California. The finding suggests powerful earthquakes — like the one that has just hit Sumatra — may trigger further quakes worldwide.
New Scientist reports that the first changes to the San Andreas occurred in 1992 after a 7.3-magnitude earthquake several hundred kilometers to the south. The second took place in 2004 after a quake of magnitude 9.1, also in Sumatra, 8,000 kilometers away. In both cases, there were distinct changes in the movement of fluids and an increase in the frequency of micro-earthquakes deep within the fault below Parkfield (Nature, DOI: 10.1038/nature08395).
Niu and colleagues believe these changes are linked to a weakening of the fault, and that monitoring them could lead to more accurate earthquake forecasts. They suggest that very large quakes might push faults all round the world closer to the point of failure, and so lead to a temporary increase in global seismicity.
-read more in Taka’aki Taira et al., “Remote Triggering of Fault-strength Changes on the San Andreas Fault at Parkfield,” Nature 461 (1 October 2009): 636-39 (doi:10.1038/nature08395)
