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5.4-Magnitude Earthquake Aftershock Has Californians on Their Toes 5.4-Magnitude Earthquake Aftershock Has Californians on Their Toes
(about 1 hour later)
Californians woke early Friday to a 5.4-magnitude aftershock, renewing fears one day after Southern California experienced its strongest earthquake in two decades.Californians woke early Friday to a 5.4-magnitude aftershock, renewing fears one day after Southern California experienced its strongest earthquake in two decades.
Susan Hough, a seismologist with the U.S. Geological Survey, said the 4:07 a.m. tremor, nine miles northeast of the Mojave Desert city of Ridgecrest where Thursday’s earthquake took place, would likely be the strongest aftershock, although more powerful ones could follow. There have been about 200 aftershocks since the 6.4-magnitude earthquake on Thursday afternoon, which led to about two dozen fire and emergency medical calls but no serious injuries. Susan Hough, a seismologist with the United States Geological Survey, said the 4:07 a.m. tremor, nine miles northeast of the Mojave Desert city of Ridgecrest near where Thursday’s earthquake took place, would likely be the strongest aftershock, although more powerful ones could follow. There have been about 200 aftershocks since the 6.4-magnitude earthquake on Thursday morning, which led to about two dozen fire and emergency medical calls but no serious injuries.
“If this is the average sequence, the magnitude 5.4 would be the largest aftershock, but aftershock sequences aren’t bound by the law of averages, and this sequence is a little more energetic than most,” Dr. Hough said. Thursday’s earthquake punctured a period of relative seismic calm in California, but scientists said it did not change their calculations of when the Big One might strike.
[A 6.4-Magnitude earthquake rattled Southern California on Thursday.] Although the faults around Ridgecrest are part of the larger San Andreas system that runs from the Gulf of California to Mendocino, north of San Francisco, Thursday’s earthquake did not relieve the stress on the San Andreas, said Paul Caruso, a geophysicist with the U.S.G.S. in Golden, Colo.
Giselle Miranda was sitting in her Palmdale, Calif., living room Friday morning putting on her shoes when she said she heard a rumbling noise from below her and a cracking sound from her walls. Her apartment quivered, and she checked on her sisters. The quake “definitely had me a little shaken up,” Ms. Miranda said, even if it lasted for only a few seconds. “We are not changing our forecast for the San Andreas,” Dr. Caruso said. “We still believe there’s a 70 percent chance of a magnitude 7 or greater in Southern California before 2030.”
Dr. Hough said she doesn’t expect the aftershocks to be felt too far from the epicenter of Thursday’s earthquake, although she cautioned that anything can happen. Seismologists are able to understand earthquake patterns in retrospect, but it is much more difficult to predict patterns until events are over, she said. The San Andreas fault, which runs near heavily populated areas and defines the boundary between the North American and Pacific tectonic plates, is considered the biggest seismic threat to California. Related cracks in the earth, like the Hayward fault that runs through Oakland and Berkeley in the San Francisco Bay Area, are also considered major threats.
Seismologists have puzzled over why these big faults have been relatively quiet in recent decades. At the same time, experts have warned that California remains unprepared for a big quake in many keys areas, including low take-up of earthquake insurance and buildings that are likely to suffer major damage.
Even though it occurred on minor faults, Thursday’s earthquake could be felt as far away as San Francisco and Phoenix. Around 50,000 people reported on the U.S.G.S. website that they felt the shaking.
[A 6.4-magnitude earthquake rattled Southern California on Thursday.]
On Friday morning, Giselle Miranda was sitting in her Palmdale, Calif., living room putting on her shoes when she said she heard a rumbling noise from below and a cracking sound from the walls. Her apartment quivered, and she checked on her sisters. The quake “definitely had me a little shaken up,” Ms. Miranda said, even if it lasted for only a few seconds.
Dr. Hough said she doesn’t expect the aftershocks to be felt too far from the epicenter of Thursday’s earthquake, although she cautioned that anything could happen. Seismologists are able to understand earthquake patterns in retrospect, but it is much more difficult to predict patterns until events are over, she said.
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The aftershock was about 32 times less powerful than the Thursday earthquake. (A whole number increase in earthquake magnitude corresponds with a 10-fold increase in the amplitude of seismogram waves, but a 31.6 increase in strength.) The epicenter of the Friday aftershock was about nine miles northeast of Ridgecrest and about five miles from the epicenter of Thursday’s quake. The epicenter of the Friday aftershock was about nine miles northeast of Ridgecrest and about five miles from the epicenter of Thursday’s quake.
Dr. Hough said a wry line attributed to Charles Richter, the man who developed the scale used to measure earthquake strength, holds up: “When you get a lot of earthquakes, you get a lot of earthquakes.”Dr. Hough said a wry line attributed to Charles Richter, the man who developed the scale used to measure earthquake strength, holds up: “When you get a lot of earthquakes, you get a lot of earthquakes.”
“This is the time in California where you want to stay on your toes,” Dr. Hough said. “This is the time in California where you want to stay on your toes,” she said.