The study analyzed 20 years of data in the Parkfield area of Central California, which sits on the fault, and found that the disastrous earthquake weakened the fault, changing both the frequency and strength of earthquakes here. 'So you will have many earthquakes, but the magnitude will be smaller than expected,' said Taka'aki Taira, a seismologist at Berkeley who headed the study. Similar small earthquakes followed the 1992 Landers earthquake in San Bernardino County in Southern California, the study found. David Shelly, a seismologist with the U.S. Geological Survey, said the study's conclusions are speculative. 'The effects from the Sumatra earthquake are fairly subtle, and it's not entirely clear how widespread it might be,' he said. Taira acknowledged that the study's scope is limited and they are continuing to look at more data. But the results also could reflect changes in other areas, he said. 'We speculated that maybe the Sumatra earthquake affected other areas in the world,' he said. 'It's still an open question.' 