In a recent issue of Nature, U.S. seismologists report that the devastating earthquake of 2004 that caused tsunamis in the Indian Ocean had also affected California’s San Andreas Fault. The tsunamis that resulted from the earthquake, which was recorded as a magnitude of 9.2, the second largest reading ever recorded, caused the death of 230,000 people living mostly in Indonesia, Thailand, India and Sri Lanka.
The study shows that in the following years of 2005 and 2006, an unusually high number of magnitude 8 earthquakes occurred, leading researchers to hypothesize that these earthquakes weaken other faults. By studying the past 20 years of seismic records for Parkfield, Calif., which is located adjacent to the San Andreas Fault, the researchers were able to develop an association between the magnitude of seismic activity in the region, which occurs regularly at levels ranging from microquakes to more significant fault movements, and distant seismic events. The data shows that large events can cause a weakening of other faults around the world, leading to an increased number and magnitude of earthquakes.