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Nearly 40 small aftershocks struck on the Calaveras Fault on Wednesday, following Tuesday night's moderate earthquake near San Jose that startled residents throughout the Bay Area. The 5.6-magnitude quake caused only minor damage in South Bay communities, and the aftershocks - the largest at 3:54 p.m. with a magnitude of 3.7 - occurred south of the main quake's epicenter near the Calaveras Reservoir. Damage from the quake was minor but widespread near the quake's epicenter. There were small landslides, a downed tree and damage to a trestle bridge in Alum Rock Park, and one landslide partially blocked a road in the park, which is perched in the hills east of downtown San Jose. The succession of aftershocks indicated that the fault was rupturing southward - a good sign - because most of the main quake's energy was being dissipated well away from the more dangerous Hayward Fault to the north. But there is always the possibility that the quake's abrupt release of stress inside the Calaveras Fault might have changed stresses that have long built up within the Hayward Fault. The most recent official report by earthquake experts has placed the probability that a destructive quake will strike within the next 25 years on the Hayward Fault with a magnitude of 6.7 or greater at 27 percent. It also estimated the probability of a similar quake on the Calaveras at 11 percent in the same period.
In the first real-world disaster test of local cellular networks, thousands of mobile phone users were unable to connect calls in the hour following the 5.6 earthquake that struck the Bay Area shortly after 8 p.m. Tuesday. Wireless carriers said traffic spiked up to 10 times higher than normal. The flood of calls also tied up AT&T's landline phone service. Wireless officials are urging users to use text messages if they have to contact someone because it's more reliable and far less intensive on the network.