Linearly with time over 2-week intervals. The strainĬhanges estimated for the first several years assume that strain changes This network straddles the San Andreas fault. PEARBLOSSOM: Data starts in late 1980 when measurements were made several The secular rates have been removed from the strain data and the rates are The date of the Landers earthquake is specified as a reference date and theĮrror grows in time relative to this date. Random walk motions of each geodetic monument of approximately 1 mm/sqrt(yr). The error accounts for the instrument precision of 0.1ppm and the The error bars represent one standard deviation about the estimate of strainĬhange. In general, the vertical line denotes the time of the 1992 Landers Of strain changes from the Pinon Flat network Of strain changes from the Buttes network Of strain changes from the Pearblossom network Make distance measurements on approximately one dozen baselines. Person crew to be on-site to run the instrument and set-up the reflectors to Each measurement of strain requires a 3 to 4 Times per year but the measurements at Anza and at the Buttes are madeĪpproximately once per year. Measurements at Pinon Flat and Pearblossom are made approximately 3 to 4 The maps of the networks show the location of the baselines in red, the majorįaults with dark, heavy lines, and other faults with thin lines. Geodetic monuments limit the ultimate precision in our estimate of strain These measurements is 0.1 part-per-million, but localized wobble of the Surface, aseismic slip is not apparent, these radial networks are idealįor measuring the 3 components of the tensor strain. These networks are radial withĪpproximately 12 baselines using a common, central station. This map shows the locations of 4 two-color EDM (Electronic Distance The San Andreas fault system in this region. The biggest aftershock registered a magnitude 4.6.Four EDM networks located in Southern California show strain accumulation on Shaking from Tuesday's quake was felt as far away as the San Francisco Bay area, the U.S. "It is not unusual to have earthquakes of this size in this region," she told a news conference. Tuesday's temblor struck in a seismically active area where several tectonic plates converge on the sea floor about 2 miles offshore, an area that has produced about 40 quakes in the 6.0 to 7.0 range over the past century, said Cynthia Pridmore, a senior geologist for the California Geological Survey. While earthquakes are routine in California, tremors at a magnitude 6.4 are less common and potentially dangerous. It was just the sensation and that general low rumbling sound of the foundation of the whole house vibrating," he said.Ĭalifornia's earthquake early warning system sent electronic alerts to the mobile devices of some 3 million northern California residents 10 seconds before the first shaking was even felt, said state emergency chief Mark Ghilarducci. "The shaking was really intense," said Daniel Holsapple, 33, a resident of nearby Arcata, who recounted grabbing his pet cat and running outside after he was jostled awake in pitch darkness by the motion of the house and by an emergency alert from his cellphone. The California Highway Patrol also said the roadway foundation there was at risk of sliding.Īuthorities reported at least four Humboldt County roads shut down due to earthquake damage. Police closed a bridge over the Eel River just outside Ferndale, a picturesque town notable for its gingerbread-style Victorian storefronts and homes, after four large cracks were discovered in the span. Two of the most serious cases were a head injury and a broken hip, officials said. Most of the 12 survivors known to have sought medical care got themselves to hospitals and sustained relatively minor injuries, many from fallen objects. The two fatalities involved individuals, one aged 72, the other 83, who suffered medical emergencies that coincided with the quake, preventing rescue teams from reaching them in time to render life-saving care, said Humboldt County Sheriff William Honsal. "The TV was coming down, the microwave, everything, like all my little knickknacks were crashing everywhere."įire officials said dispatchers fielded roughly 70 emergency calls after the quake.ĭetails of casualties were sketchy. "And it just kept shaking and shaking, and things were crashing," she recalled.
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